   SusanAngebranndtDigital Equipment
   CorporationRaymondDrewryDigital Equipment
   CorporationPhilipKarltonDigital Equipment
   CorporationToddNewmanDigital Equipment
   CorporationBobScheiflerMassachusetts Institute of
   TechnologyKeithPackardMIT X ConsortiumDavidP.WigginsX
   ConsortiumJimGettysX.org Foundation and Hewlett PackardThe
   X.Org Foundation2004Definition of the Porting Layer for the X
   v11 Sample ServerX Porting Layer1.027 Oct 2004saInitial
   Version1.127 Oct 2004bsMinor Revisions2.027 Oct 2004kpRevised
   for Release 4 and 53.027 Oct 2004dpwRevised for Release 63.127
   Oct 2004jgRevised for Release 6.8.23.217 Dec 2006efwDocBook
   conversionCopyright © 1994 X Consortium, Inc., 2004 X.org
   Foundation, Inc.Permission is hereby granted, free of charge,
   to any person obtaining a copy of this software and associated
   documentation files (the ``Software''), to deal in the Software
   without restriction, including without limitation the rights to
   use, copy, modify, merge, publish, distribute, sublicense,
   and/or sell copies of the Software, and to permit persons to
   whom the Software is furnished to do so, subject to the
   following conditions:The above copyright notice and this
   permission notice shall be included in all copies or
   substantial portions of the Software.THE SOFTWARE IS PROVIDED
   ``AS IS'', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO
   EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES
   OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
   OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
   SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.LK201 and
   DEC are trademarks of Digital Equipment Corporation. Macintosh
   and Apple are trademarks of Apple Computer, Inc. PostScript is
   a trademark of Adobe Systems, Inc. Ethernet is a trademark of
   Xerox Corporation. X Window System is a trademark of the X.org
   Foundation, Inc. Cray is a trademark of Cray Research, Inc.The
   following document explains the structure of the X Window
   System display server and the interfaces among the larger
   pieces. It is intended as a reference for programmers who are
   implementing an X Display Server on their workstation hardware.
   It is included with the X Window System source tape, along with
   the document "Strategies for Porting the X v11 Sample Server."
   The order in which you should read these documents is: Read the
   first section of the "Strategies for Porting" document
   (Overview of Porting Process).Skim over this document (the
   Definition document).Skim over the remainder of the Strategies
   document.Start planning and working, referring to the
   Strategies and Definition documents. You may also want to look
   at the following documents: "The X Window System" for an
   overview of X."Xlib - C Language X Interface" for a view of
   what the client programmer sees."X Window System Protocol" for
   a terse description of the byte stream protocol between the
   client and server. To understand this document and the
   accompanying source code, you should know the C language. You
   should be familiar with 2D graphics and windowing concepts such
   as clipping, bitmaps, fonts, etc. You should have a general
   knowledge of the X Window System. To implement the server code
   on your hardware, you need to know a lot about your hardware,
   its graphic display device(s), and (possibly) its networking
   and multitasking facilities. This document depends a lot on the
   source code, so you should have a listing of the code
   handy.Some source in the distribution is directly compilable on
   your machine. Some of it will require modification. Other parts
   may have to be completely written from scratch. The
   distribution also includes source for a sample implementation
   of a display server which runs on a very wide variety of color
   and monochrome displays on Linux and *BSD which you will find
   useful for implementing any type of X server.Note to the 2004
   edition: at this time this document must be considered
   incomplete. In particular, the new Render extension is still
   lacking good documentation, and has become vital to high
   performance X implementations. A new "fb" portable frame buffer
   graphics library (replacing "cfb") is used by most
   implementations to implement software rendering for most
   operations. Accelerating only a few of the old "core" graphics
   functions is now needed, as performance in software is "good
   enough" for most operations. Modern applications and desktop
   environments are now much more sensitive to good implementation
   of the Render extension than in most operations of the old X
   graphics model. The shadow frame buffer implementation is also
   very useful in many circumstances, and also needs
   documentation. We hope to rectify these shortcomings in our
   documentation in the future. Help would be greatly
   appreciated.The X Window System The X Window System, or simply
   "X," is a windowing system that provides high-performance,
   high-level, device-independent graphics. X is a windowing
   system designed for bitmapped graphic displays. The display can
   have a simple, monochrome display or it can have a color
   display with up to 32 bits per pixel with a special graphics
   processor doing the work. (In this document, monochrome means a
   black and white display with one bit per pixel. Even though the
   usual meaning of monochrome is more general, this special case
   is so common that we decided to reserve the word for this
   purpose.) In practice, monochrome displays are now almost
   unheard of, with 4 bit gray scale displays being the low end. X
   is designed for a networking environment where users can run
   applications on machines other than their own workstations.
   Sometimes, the connection is over an Ethernet network with a
   protocol such as TCP/IP; but, any "reliable" byte stream is
   allowable. A high-bandwidth byte stream is preferable; RS-232
   at 9600 baud would be slow without compression techniques. X by
   itself allows great freedom of design. For instance, it does
   not include any user interface standard. Its intent is to
   "provide mechanism, not policy." By making it general, it can
   be the foundation for a wide variety of interactive software.
   For a more detailed overview, see the document "The X Window
   System." For details on the byte stream protocol, see "X Window
   System protocol." Overview of the Server The display server
   manages windows and simple graphics requests for the user on
   behalf of different client applications. The client
   applications can be running on any machine on the network. The
   server mainly does three things: Responds to protocol requests
   from existing clients (mostly graphic and text drawing
   commands)Sends device input (keystrokes and mouse actions) and
   other events to existing clientsMaintains client connections
   The server code is organized into four major pieces: Device
   Independent (DIX) layer - code shared among all
   implementationsOperating System (OS) layer - code that is
   different for each operating system but is shared among all
   graphic devices for this operating systemDevice Dependent (DDX)
   layer - code that is (potentially) different for each
   combination of operating system and graphic deviceExtension
   Interface - a standard way to add features to the X server The
   "porting layer" consists of the OS and DDX layers; these are
   actually parallel and neither one is on top of the other. The
   DIX layer is intended to be portable without change to target
   systems and is not detailed here, although several routines in
   DIX that are called by DDX are documented. Extensions
   incorporate new functionality into the server; and require
   additional functionality over a simple DDX. The following
   sections outline the functions of the layers. Section 3 briefly
   tells what you need to know about the DIX layer. The OS layer
   is explained in Section 4. Section 5 gives the theory of
   operation and procedural interface for the DDX layer. Section 6
   describes the functions which exist for the extension writer.
   DIX Layer The DIX layer is the machine and device independent
   part of X. The source should be common to all operating systems
   and devices. The port process should not include changes to
   this part, therefore internal interfaces to DIX modules are not
   discussed, except for public interfaces to the DDX and the OS
   layers. The functions described in this section are available
   for extension writers to use. In the process of getting your
   server to work, if you think that DIX must be modified for
   purposes other than bug fixes, you may be doing something
   wrong. Keep looking for a more compatible solution. When the
   next release of the X server code is available, you should be
   able to just drop in the new DIX code and compile it. If you
   change DIX, you will have to remember what changes you made and
   will have to change the new sources before you can update to
   the new version. The heart of the DIX code is a loop called the
   dispatch loop. Each time the processor goes around the loop, it
   sends off accumulated input events from the input devices to
   the clients, and it processes requests from the clients. This
   loop is the most organized way for the server to process the
   asynchronous requests that it needs to process. Most of these
   operations are performed by OS and DDX routines that you must
   supply. Server Resource System X resources are C structs inside
   the server. Client applications create and manipulate these
   objects according to the rules of the X byte stream protocol.
   Client applications refer to resources with resource IDs, which
   are 32-bit integers that are sent over the network. Within the
   server, of course, they are just C structs, and we refer to
   them by pointers. Pre-Defined Resource Types The DDX layer has
   several kinds of resources:
   WindowPixmapScreenDeviceColormapFontCursorGraphics Contexts The
   type names of the more important server structs usually end in
   "Rec," such as "DeviceRec;" the pointer types usually end in
   "Ptr," such as "DevicePtr." The structs and important defined
   constants are declared in .h files that have names that suggest
   the name of the object. For instance, there are two .h files
   for windows, window.h and windowstr.h. window.h defines only
   what needs to be defined in order to use windows without
   peeking inside of them; windowstr.h defines the structs with
   all of their components in great detail for those who need it.
   Three kinds of fields are in these structs: Attribute fields -
   struct fields that contain values like normal structsPointers
   to procedures, or structures of procedures, that operate on the
   objectA private field (or two) used by your DDX code to keep
   private data (probably a pointer to another data structure), or
   an array of private fields, which is sized as the server
   initializes. DIX calls through the struct's procedure pointers
   to do its tasks. These procedures are set either directly or
   indirectly by DDX procedures. Most of the procedures described
   in the remainder of this document are accessed through one of
   these structs. For example, the procedure to create a pixmap is
   attached to a ScreenRec and might be called by using the
   expression (* pScreen->CreatePixmap)(pScreen, width, height,
   depth). All procedure pointers must be set to some routine
   unless noted otherwise; a null pointer will have unfortunate
   consequences. Procedure routines will be indicated in the
   documentation by this convention: void
   pScreen->MyScreenRoutine(arg, arg, ...) as opposed to a free
   routine, not in a data structure: void MyFreeRoutine(arg, arg,
   ...) The attribute fields are mostly set by DIX; DDX should not
   modify them unless noted otherwise. Creating Resources and
   Resource Types These functions should also be called from your
   extensionInitProc to allocate all of the various resource
   classes and types required for the extension. Each time the
   server resets, these types must be reallocated as the old
   allocations will have been discarded. Resource types are
   integer values starting at 1. Get a resource type by calling
   RESTYPE CreateNewResourceType(deleteFunc) deleteFunc will be
   called to destroy all resources with this type. Resource
   classes are masks starting at 1 << 31 which can be or'ed with
   any resource type to provide attributes for the type. To
   allocate a new class bit, call RESTYPE CreateNewResourceClass()
   There are two ways of looking up resources, by type or by
   class. Classes are non-exclusive subsets of the space of all
   resources, so you can lookup the union of multiple classes.
   (RC_ANY is the union of all classes). Note that the appropriate
   class bits must be or'ed into the value returned by
   CreateNewResourceType when calling resource lookup functions.
   If you need to create a ``private'' resource ID for internal
   use, you can call FakeClientID. XID FakeClientID(client) int
   client; This allocates from ID space reserved for the server.
   To associate a resource value with an ID, use AddResource. Bool
   AddResource(id, type, value) XID id; RESTYPE type; pointer
   value; The type should be the full type of the resource,
   including any class bits. If AddResource fails to allocate
   memory to store the resource, it will call the deleteFunc for
   the type, and then return False. To free a resource, use one of
   the following. void FreeResource(id, skipDeleteFuncType) XID
   id; RESTYPE skipDeleteFuncType; void FreeResourceByType(id,
   type, skipFree) XID id; RESTYPE type; Bool skipFree;
   FreeResource frees all resources matching the given id,
   regardless of type; the type's deleteFunc will be called on
   each matching resource, except that skipDeleteFuncType can be
   set to a single type for which the deleteFunc should not be
   called (otherwise pass RT_NONE). FreeResourceByType frees a
   specific resource matching a given id and type; if skipFree is
   true, then the deleteFunc is not called. Looking Up Resources
   To look up a resource, use one of the following. pointer
   LookupIDByType(id, rtype) XID id; RESTYPE rtype; pointer
   LookupIDByClass(id, classes) XID id; RESTYPE classes;
   LookupIDByType finds a resource with the given id and exact
   type. LookupIDByClass finds a resource with the given id whose
   type is included in any one of the specified classes.Callback
   Manager To satisfy a growing number of requests for the
   introduction of ad hoc notification style hooks in the server,
   a generic callback manager was introduced in R6. A callback
   list object can be introduced for each new hook that is
   desired, and other modules in the server can register interest
   in the new callback list. The following functions support these
   operations. Before getting bogged down in the interface
   details, an typical usage example should establish the
   framework. Let's look at the ClientStateCallback in
   dix/dispatch.c. The purpose of this particular callback is to
   notify intereseted parties when a client's state (initial,
   running, gone) changes. The callback is "created" in this case
   by simply declaring a variable: CallbackListPtr
   ClientStateCallback; Whenever the client's state changes, the
   following code appears, which notifies all intereseted parties
   of the change: if (ClientStateCallback)
   CallCallbacks(&ClientStateCallback, (pointer)client);
   Interested parties subscribe to the ClientStateCallback list by
   saying: AddCallback(&ClientStateCallback, func, data); When
   CallCallbacks is invoked on the list, func will be called
   thusly: (*func)(&ClientStateCallback, data, client) Now for the
   details. Bool CreateCallbackList(pcbl, cbfuncs) CallbackListPtr
   *pcbl; CallbackFuncsPtr cbfuncs; CreateCallbackList creates a
   callback list. We envision that this function will be rarely
   used because the callback list is created automatically (if it
   doesn't already exist) when the first call to AddCallback is
   made on the list. The only reason to explicitly create the
   callback list with this function is if you want to override the
   implementation of some of the other operations on the list by
   passing your own cbfuncs. You also lose something by explicit
   creation: you introduce an order dependency during server
   startup because the list must be created before any modules
   subscribe to it. Returns TRUE if successful. Bool
   AddCallback(pcbl, callback, subscriber_data) CallbackListPtr
   *pcbl; CallbackProcPtr callback; pointer subscriber_data; Adds
   the (callback, subscriber_data) pair to the given callback
   list. Creates the callback list if it doesn't exist. Returns
   TRUE if successful. Bool DeleteCallback(pcbl, callback,
   subscriber_data) CallbackListPtr *pcbl; CallbackProcPtr
   callback; pointer subscriber_data; Removes the (callback, data)
   pair to the given callback list if present. Returns TRUE if
   (callback, data) was found. void CallCallbacks(pcbl, call_data)
   CallbackListPtr *pcbl; pointer call_data; For each callback
   currently registered on the given callback list, call it as
   follows: (*callback)(pcbl, subscriber_data, call_data); void
   DeleteCallbackList(pcbl) CallbackListPtr *pcbl; Destroys the
   given callback list.Extension Interfaces This function should
   be called from your extensionInitProc which should be called by
   InitExtensions. ExtensionEntry *AddExtension(name,
   NumEvents,NumErrors, MainProc, SwappedMainProc, CloseDownProc,
   MinorOpcodeProc) char *name; /*Null terminate string; case
   matters*/ int NumEvents; int NumErrors; int (*
   MainProc)(ClientPtr);/*Called if client matches server order*/
   int (* SwappedMainProc)(ClientPtr);/*Called if client differs
   from server*/ void (* CloseDownProc)(ExtensionEntry *);
   unsigned short (*MinorOpcodeProc)(ClientPtr); name is the name
   used by clients to refer to the extension. NumEvents is the
   number of event types used by the extension, NumErrors is the
   number of error codes needed by the extension. MainProc is
   called whenever a client accesses the major opcode assigned to
   the extension. SwappedMainProc is identical, except the client
   using the extension has reversed byte-sex. CloseDownProc is
   called at server reset time to deallocate any private storage
   used by the extension. MinorOpcodeProc is used by DIX to place
   the appropriate value into errors. The DIX routine
   StandardMinorOpcode can be used here which takes the minor
   opcode from the normal place in the request (i.e. just after
   the major opcode).Macros and Other Helpers There are a number
   of macros in Xserver/include/dix.h which are useful to the
   extension writer. Ones of particular interest are: REQUEST,
   REQUEST_SIZE_MATCH, REQUEST_AT_LEAST_SIZE, REQUEST_FIXED_SIZE,
   LEGAL_NEW_RESOURCE, LOOKUP_DRAWABLE, VERIFY_GC, and
   VALIDATE_DRAWABLE_AND_GC. Useful byte swapping macros can be
   found in Xserver/include/misc.h: lswapl, lswaps, LengthRestB,
   LengthRestS, LengthRestL, SwapRestS, SwapRestL, swapl, swaps,
   cpswapl, and cpswaps.OS Layer This part of the source consists
   of a few routines that you have to rewrite for each operating
   system. These OS functions maintain the client connections and
   schedule work to be done for clients. They also provide an
   interface to font files, font name to file name translation,
   and low level memory management. void OsInit() OsInit
   initializes your OS code, performing whatever tasks need to be
   done. Frequently there is not much to be done. The sample
   server implementation is in Xserver/os/osinit.c. Scheduling and
   Request Delivery The main dispatch loop in DIX creates the
   illusion of multitasking between different windows, while the
   server is itself but a single process. The dispatch loop breaks
   up the work for each client into small digestible parts. Some
   parts are requests from a client, such as individual graphic
   commands. Some parts are events delivered to the client, such
   as keystrokes from the user. The processing of events and
   requests for different clients can be interleaved with one
   another so true multitasking is not needed in the server. You
   must supply some of the pieces for proper scheduling between
   clients. int WaitForSomething(pClientReady) int *pClientReady;
   WaitForSomething is the scheduler procedure you must write that
   will suspend your server process until something needs to be
   done. This call should make the server suspend until one or
   more of the following occurs: There is an input event from the
   user or hardware (see SetInputCheck())There are requests
   waiting from known clients, in which case you should return a
   count of clients stored in pClientReadyA new client tries to
   connect, in which case you should create the client and then
   continue waiting Before WaitForSomething() computes the masks
   to pass to select, poll or similar operating system interface,
   it needs to see if there is anything to do on the work queue;
   if so, it must call a DIX routine called ProcessWorkQueue.
   extern WorkQueuePtr workQueue; if (workQueue) ProcessWorkQueue
   (); If WaitForSomething() decides it is about to do something
   that might block (in the sample server, before it calls
   select() or poll) it must call a DIX routine called
   BlockHandler(). void BlockHandler(pTimeout, pReadmask) pointer
   pTimeout; pointer pReadmask; The types of the arguments are for
   agreement between the OS and DDX implementations, but the
   pTimeout is a pointer to the information determining how long
   the block is allowed to last, and the pReadmask is a pointer to
   the information describing the descriptors that will be waited
   on. In the sample server, pTimeout is a struct timeval **, and
   pReadmask is the address of the select() mask for reading. The
   DIX BlockHandler() iterates through the Screens, for each one
   calling its BlockHandler. A BlockHandler is declared thus: void
   xxxBlockHandler(nscreen, pbdata, pptv, pReadmask) int nscreen;
   pointer pbdata; struct timeval ** pptv; pointer pReadmask; The
   arguments are the index of the Screen, the blockData field of
   the Screen, and the arguments to the DIX BlockHandler().
   Immediately after WaitForSomething returns from the block, even
   if it didn't actually block, it must call the DIX routine
   WakeupHandler(). void WakeupHandler(result, pReadmask) int
   result; pointer pReadmask; Once again, the types are not
   specified by DIX. The result is the success indicator for the
   thing that (may have) blocked, and the pReadmask is a mask of
   the descriptors that came active. In the sample server, result
   is the result from select() (or equivalent operating system
   function), and pReadmask is the address of the select() mask
   for reading. The DIX WakeupHandler() calls each Screen's
   WakeupHandler. A WakeupHandler is declared thus: void
   xxxWakeupHandler(nscreen, pbdata, err, pReadmask) int nscreen;
   pointer pbdata; unsigned long result; pointer pReadmask; The
   arguments are the index of the Screen, the blockData field of
   the Screen, and the arguments to the DIX WakeupHandler(). In
   addition to the per-screen BlockHandlers, any module may
   register block and wakeup handlers (only together) using: Bool
   RegisterBlockAndWakeupHandlers (blockHandler, wakeupHandler,
   blockData) BlockHandlerProcPtr blockHandler;
   WakeupHandlerProcPtr wakeupHandler; pointer blockData; A FALSE
   return code indicates that the registration failed for lack of
   memory. To remove a registered Block handler at other than
   server reset time (when they are all removed automatically),
   use: RemoveBlockAndWakeupHandlers (blockHandler, wakeupHandler,
   blockData) BlockHandlerProcPtr blockHandler;
   WakeupHandlerProcPtr wakeupHandler; pointer blockData; All
   three arguments must match the values passed to
   RegisterBlockAndWakeupHandlers. These registered block handlers
   are called after the per-screen handlers: void (*BlockHandler)
   (blockData, pptv, pReadmask) pointer blockData; OSTimePtr pptv;
   pointer pReadmask; Sometimes block handlers need to adjust the
   time in a OSTimePtr structure, which on UNIX family systems is
   generally represented by a struct timeval consisting of seconds
   and microseconds in 32 bit values. As a convenience to reduce
   error prone struct timeval computations which require modulus
   arithmetic and correct overflow behavior in the face of
   millisecond wrapping throrugh 32 bits, void
   AdjustWaitForDelay(pointer /*waitTime*, unsigned long /*
   newdelay */) has been provided. Any wakeup handlers registered
   with RegisterBlockAndWakeupHandlers will be called before the
   Screen handlers: void (*WakeupHandler) (blockData, err,
   pReadmask) pointer blockData; int err; pointer pReadmask; The
   WaitForSomething on the sample server also has a built in
   screen saver that darkens the screen if no input happens for a
   period of time. The sample server implementation is in
   Xserver/os/WaitFor.c. Note that WaitForSomething() may be
   called when you already have several outstanding things
   (events, requests, or new clients) queued up. For instance,
   your server may have just done a large graphics request, and it
   may have been a long time since WaitForSomething() was last
   called. If many clients have lots of requests queued up, DIX
   will only service some of them for a given client before going
   on to the next client (see isItTimeToYield, below). Therefore,
   WaitForSomething() will have to report that these same clients
   still have requests queued up the next time around. An
   implementation should return information on as many outstanding
   things as it can. For instance, if your implementation always
   checks for client data first and does not report any input
   events until there is no client data left, your mouse and
   keyboard might get locked out by an application that constantly
   barrages the server with graphics drawing requests. Therefore,
   as a general rule, input devices should always have priority
   over graphics devices. A list of indexes (client->index) for
   clients with data ready to be read or processed should be
   returned in pClientReady, and the count of indexes returned as
   the result value of the call. These are not clients that have
   full requests ready, but any clients who have any data ready to
   be read or processed. The DIX dispatcher will process requests
   from each client in turn by calling ReadRequestFromClient(),
   below. WaitForSomething() must create new clients as they are
   requested (by whatever mechanism at the transport level). A new
   client is created by calling the DIX routine: ClientPtr
   NextAvailableClient(ospriv) pointer ospriv; This routine
   returns NULL if a new client cannot be allocated (e.g. maximum
   number of clients reached). The ospriv argument will be stored
   into the OS private field (pClient->osPrivate), to store OS
   private information about the client. In the sample server, the
   osPrivate field contains the number of the socket for this
   client. See also "New Client Connections."
   NextAvailableClient() will call InsertFakeRequest(), so you
   must be prepared for this. If there are outstanding input
   events, you should make sure that the two SetInputCheck()
   locations are unequal. The DIX dispatcher will call your
   implementation of ProcessInputEvents() until the
   SetInputCheck() locations are equal. The sample server contains
   an implementation of WaitForSomething(). The following two
   routines indicate to WaitForSomething() what devices should be
   waited for. fd is an OS dependent type; in the sample server it
   is an open file descriptor. int AddEnabledDevice(fd) int fd;
   int RemoveEnabledDevice(fd) int fd; These two routines are
   usually called by DDX from the initialize cases of the Input
   Procedures that are stored in the DeviceRec (the routine passed
   to AddInputDevice()). The sample server implementation of
   AddEnabledDevice and RemoveEnabledDevice are in
   Xserver/os/connection.c. Timer Facilities Similarly, the X
   server or an extension may need to wait for some timeout. Early
   X releases implemented this functionality using block and
   wakeup handlers, but this has been rewritten to use a general
   timer facilty, and the internal screen saver facilties
   reimplemented to use Timers. These functions are TimerInit,
   TimerForce, TimerSet, TimerCheck, TimerCancel, and TimerFree,
   as defined in Xserver/include/os.h. A callback function will be
   called when the timer fires, along with the current time, and a
   user provided argument. typedef struct _OsTimerRec *OsTimerPtr;
   typedef CARD32 (*OsTimerCallback)( OsTimerPtr /* timer */,
   CARD32 /* time */, pointer /* arg */); OsTimerPtr TimerSet(
   OsTimerPtr /* timer */, int /* flags */, CARD32 /* millis */,
   OsTimerCallback /* func */, pointer /* arg */); TimerSet
   returns a pointer to a timer structure and sets a timer to the
   specified time with the specified argument. The flags can be
   TimerAbsolute and TimerForceOld. The TimerSetOld flag controls
   whether if the timer is reset and the timer is pending, the
   whether the callback function will get called. The
   TimerAbsolute flag sets the callback time to an absolute time
   in the future rather than a time relative to when TimerSet is
   called. TimerFree should be called to free the memory allocated
   for the timer entry. void TimerInit(void) Bool
   TimerForce(OsTimerPtr /* pTimer */) void TimerCheck(void); void
   TimerCancel(OsTimerPtr /* pTimer */) void TimerFree(OSTimerPtr
   /* pTimer */) TimerInit frees any exisiting timer entries.
   TimerForce forces a call to the timer's callback function and
   returns true if the timer entry existed, else it returns false
   and does not call the callback function. TimerCancel will
   cancel the specified timer. TimerFree calls TimerCancel and
   frees the specified timer. Calling TimerCheck will force the
   server to see if any timer callbacks should be called. New
   Client Connections The process whereby a new client-server
   connection starts up is very dependent upon what your byte
   stream mechanism. This section describes byte stream initiation
   using examples from the TCP/IP implementation on the sample
   server. The first thing that happens is a client initiates a
   connection with the server. How a client knows to do this
   depends upon your network facilities and the Xlib
   implementation. In a typical scenario, a user named Fred on his
   X workstation is logged onto a Cray supercomputer running a
   command shell in an X window. Fred can type shell commands and
   have the Cray respond as though the X server were a dumb
   terminal. Fred types in a command to run an X client
   application that was linked with Xlib. Xlib looks at the shell
   environment variable DISPLAY, which has the value
   "fredsbittube:0.0." The host name of Fred's workstation is
   "fredsbittube," and the 0s are for multiple screens and
   multiple X server processes. (Precisely what happens on your
   system depends upon how X and Xlib are implemented.) The client
   application calls a TCP routine on the Cray to open a TCP
   connection for X to communicate with the network node
   "fredsbittube." The TCP software on the Cray does this by
   looking up the TCP address of "fredsbittube" and sending an
   open request to TCP port 6000 on fredsbittube. All X servers on
   TCP listen for new clients on port 6000 by default; this is
   known as a "well-known port" in IP terminology. The server
   receives this request from its port 6000 and checks where it
   came from to see if it is on the server's list of "trustworthy"
   hosts to talk to. Then, it opens another port for
   communications with the client. This is the byte stream that
   all X communications will go over. Actually, it is a bit more
   complicated than that. Each X server process running on the
   host machine is called a "display." Each display can have more
   than one screen that it manages. "corporatehydra:3.2"
   represents screen 2 on display 3 on the multi-screened network
   node corporatehydra. The open request would be sent on
   well-known port number 6003. Once the byte stream is set up,
   what goes on does not depend very much upon whether or not it
   is TCP. The client sends an xConnClientPrefix struct (see
   Xproto.h) that has the version numbers for the version of Xlib
   it is running, some byte-ordering information, and two
   character strings used for authorization. If the server does
   not like the authorization strings or the version numbers do
   not match within the rules, or if anything else is wrong, it
   sends a failure response with a reason string. If the
   information never comes, or comes much too slowly, the
   connection should be broken off. You must implement the
   connection timeout. The sample server implements this by
   keeping a timestamp for each still-connecting client and, each
   time just before it attempts to accept new connections, it
   closes any connection that are too old. The connection timeout
   can be set from the command line. You must implement whatever
   authorization schemes you want to support. The sample server on
   the distribution tape supports a simple authorization scheme.
   The only interface seen by DIX is: char *
   ClientAuthorized(client, proto_n, auth_proto, string_n,
   auth_string) ClientPtr client; unsigned int proto_n; char
   *auth_proto; unsigned int string_n; char *auth_string; DIX will
   only call this once per client, once it has read the full
   initial connection data from the client. If the connection
   should be accepted ClientAuthorized() should return NULL, and
   otherwise should return an error message string. Accepting new
   connections happens internally to WaitForSomething().
   WaitForSomething() must call the DIX routine
   NextAvailableClient() to create a client object. Processing of
   the initial connection data will be handled by DIX. Your OS
   layer must be able to map from a client to whatever information
   your OS code needs to communicate on the given byte stream to
   the client. DIX uses this ClientPtr to refer to the client from
   now on. The sample server uses the osPrivate field in the
   ClientPtr to store the file descriptor for the socket, the
   input and output buffers, and authorization information. To
   initialize the methods you choose to allow clients to connect
   to your server, main() calls the routine void
   CreateWellKnownSockets() This routine is called only once, and
   not called when the server is reset. To recreate any sockets
   during server resets, the following routine is called from the
   main loop: void ResetWellKnownSockets() Sample implementations
   of both of these routines are found in Xserver/os/connection.c.
   For more details, see the section called "Connection Setup" in
   the X protocol specification. Reading Data from Clients
   Requests from the client are read in as a byte stream by the OS
   layer. They may be in the form of several blocks of bytes
   delivered in sequence; requests may be broken up over block
   boundaries or there may be many requests per block. Each
   request carries with it length information. It is the
   responsibility of the following routine to break it up into
   request blocks. int ReadRequestFromClient(who) ClientPtr who;
   You must write the routine ReadRequestFromClient() to get one
   request from the byte stream belonging to client "who." You
   must swap the third and fourth bytes (the second 16-bit word)
   according to the byte-swap rules of the protocol to determine
   the length of the request. This length is measured in 32-bit
   words, not in bytes. Therefore, the theoretical maximum request
   is 256K. (However, the maximum length allowed is dependent upon
   the server's input buffer. This size is sent to the client upon
   connection. The maximum size is the constant MAX_REQUEST_SIZE
   in Xserver/include/os.h) The rest of the request you return is
   assumed NOT to be correctly swapped for internal use, because
   that is the responsibility of DIX. The 'who' argument is the
   ClientPtr returned from WaitForSomething. The return value
   indicating status should be set to the (positive) byte count if
   the read is successful, 0 if the read was blocked, or a
   negative error code if an error happened. You must then store a
   pointer to the bytes of the request in the client request
   buffer field; who->requestBuffer. This can simply be a pointer
   into your buffer; DIX may modify it in place but will not
   otherwise cause damage. Of course, the request must be
   contiguous; you must shuffle it around in your buffers if not.
   The sample server implementation is in Xserver/os/io.c.
   Inserting Data for Clients DIX can insert data into the client
   stream, and can cause a "replay" of the current request. Bool
   InsertFakeRequest(client, data, count) ClientPtr client; char
   *data; int count; int ResetCurrentRequest(client) ClientPtr
   client; InsertFakeRequest() must insert the specified number of
   bytes of data into the head of the input buffer for the client.
   This may be a complete request, or it might be a partial
   request. For example, NextAvailableCient() will insert a
   partial request in order to read the initial connection data
   sent by the client. The routine returns FALSE if memory could
   not be allocated. ResetCurrentRequest() should "back up" the
   input buffer so that the currently executing request will be
   reexecuted. DIX may have altered some values (e.g. the overall
   request length), so you must recheck to see if you still have a
   complete request. ResetCurrentRequest() should always cause a
   yield (isItTimeToYield). Sending Events, Errors And Replies To
   Clients int WriteToClient(who, n, buf) ClientPtr who; int n;
   char *buf; WriteToClient should write n bytes starting at buf
   to the ClientPtr "who". It returns the number of bytes written,
   but for simplicity, the number returned must be either the same
   value as the number requested, or -1, signaling an error. The
   sample server implementation is in Xserver/os/io.c. void
   SendErrorToClient(client, majorCode, minorCode, resId,
   errorCode) ClientPtr client; unsigned int majorCode; unsigned
   int minorCode; XID resId; int errorCode; SendErrorToClient can
   be used to send errors back to clients, although in most cases
   your request function should simply return the error code,
   having set client->errorValue to the appropriate error value to
   return to the client, and DIX will call this function with the
   correct opcodes for you. void FlushAllOutput() void
   FlushIfCriticalOutputPending() void SetCriticalOutputPending()
   These three routines may be implemented to support buffered or
   delayed writes to clients, but at the very least, the stubs
   must exist. FlushAllOutput() unconditionally flushes all output
   to clients; FlushIfCriticalOutputPending() flushes output only
   if SetCriticalOutputPending() has be called since the last time
   output was flushed. The sample server implementation is in
   Xserver/os/io.c and actually ignores requests to flush output
   on a per-client basis if it knows that there are requests in
   that client's input queue. Font Support In the sample server,
   fonts are encoded in disk files or fetched from the font
   server. For disk fonts, there is one file per font, with a file
   name like "fixed.pcf". Font server fonts are read over the
   network using the X Font Server Protocol. The disk directories
   containing disk fonts and the names of the font servers are
   listed together in the current "font path." In principle, you
   can put all your fonts in ROM or in RAM in your server. You can
   put them all in one library file on disk. You could generate
   them on the fly from stroke descriptions. By placing the
   appropriate code in the Font Library, you will automatically
   export fonts in that format both through the X server and the
   Font server. With the incorporation of font-server based fonts
   and the Speedo donation from Bitstream, the font interfaces
   have been moved into a separate library, now called the Font
   Library (../fonts/lib). These routines are shared between the X
   server and the Font server, so instead of this document
   specifying what you must implement, simply refer to the font
   library interface specification for the details. All of the
   interface code to the Font library is contained in
   dix/dixfonts.c Memory Management Memory management is based on
   functions in the C runtime library. Xalloc(), Xrealloc(), and
   Xfree() work just like malloc(), realloc(), and free(), except
   that you can pass a null pointer to Xrealloc() to have it
   allocate anew or pass a null pointer to Xfree() and nothing
   will happen. The versions in the sample server also do some
   checking that is useful for debugging. Consult a C runtime
   library reference manual for more details. The macros
   ALLOCATE_LOCAL and DEALLOCATE_LOCAL are provided in
   Xserver/include/os.h. These are useful if your compiler
   supports alloca() (or some method of allocating memory from the
   stack); and are defined appropriately on systems which support
   it. Treat memory allocation carefully in your implementation.
   Memory leaks can be very hard to find and are frustrating to a
   user. An X server could be running for days or weeks without
   being reset, just like a regular terminal. If you leak a few
   dozen k per day, that will add up and will cause problems for
   users that leave their workstations on. Client Scheduling The X
   server has the ability to schedule clients much like an
   operating system would, suspending and restarting them without
   regard for the state of their input buffers. This functionality
   allows the X server to suspend one client and continue
   processing requests from other clients while waiting for a
   long-term network activity (like loading a font) before
   continuing with the first client. Bool isItTimeToYield;
   isItTimeToYield is a global variable you can set if you want to
   tell DIX to end the client's "time slice" and start paying
   attention to the next client. After the current request is
   finished, DIX will move to the next client. In the sample
   server, ReadRequestFromClient() sets isItTimeToYield after 10
   requests packets in a row are read from the same client. This
   scheduling algorithm can have a serious effect upon performance
   when two clients are drawing into their windows simultaneously.
   If it allows one client to run until its request queue is empty
   by ignoring isItTimeToYield, the client's queue may in fact
   never empty and other clients will be blocked out. On the other
   hand, if it switchs between different clients too quickly,
   performance may suffer due to too much switching between
   contexts. For example, if a graphics processor needs to be set
   up with drawing modes before drawing, and two different clients
   are drawing with different modes into two different windows,
   you may switch your graphics processor modes so often that
   performance is impacted. See the Strategies document for
   heuristics on setting isItTimeToYield. The following functions
   provide the ability to suspend request processing on a
   particular client, resuming it at some later time: int
   IgnoreClient (who) ClientPtr who; int AttendClient (who)
   ClientPtr who; Ignore client is responsible for pretending that
   the given client doesn't exist. WaitForSomething should not
   return this client as ready for reading and should not return
   if only this client is ready. AttendClient undoes whatever
   IgnoreClient did, setting it up for input again. Three
   functions support "process control" for X clients: Bool
   ClientSleep (client, function, closure) ClientPtr client; Bool
   (*function)(); pointer closure; This suspends the current
   client (the calling routine is responsible for making its way
   back to Dispatch()). No more X requests will be processed for
   this client until ClientWakeup is called. Bool ClientSignal
   (client) ClientPtr client; This function causes a call to the
   (*function) parameter passed to ClientSleep to be queued on the
   work queue. This does not automatically "wakeup" the client,
   but the function called is free to do so by calling:
   ClientWakeup (client) ClientPtr client; This re-enables X
   request processing for the specified client. Other OS Functions
   void ErrorF(char *f, ...) void FatalError(char *f, ...) void
   Error(str) char *str; You should write these three routines to
   provide for diagnostic output from the dix and ddx layers,
   although implementing them to produce no output will not affect
   the correctness of your server. ErrorF() and FatalError() take
   a printf() type of format specification in the first argument
   and an implementation-dependent number of arguments following
   that. Normally, the formats passed to ErrorF() and FatalError()
   should be terminated with a newline. Error() provides an os
   interface for printing out the string passed as an argument
   followed by a meaningful explanation of the last system error.
   Normally the string does not contain a newline, and it is only
   called by the ddx layer. In the sample implementation, Error()
   uses the perror() function. After printing the message
   arguments, FatalError() must be implemented such that the
   server will call AbortDDX() to give the ddx layer a chance to
   reset the hardware, and then terminate the server; it must not
   return. The sample server implementation for these routines is
   in Xserver/os/util.c. Idiom Support The DBE specification
   introduces the notion of idioms, which are groups of X requests
   which can be executed more efficiently when taken as a whole
   compared to being performed individually and sequentially. This
   following server internal support to allows DBE
   implementations, as well as other parts of the server, to do
   idiom processing. xReqPtr PeekNextRequest(xReqPtr req,
   ClientPtr client, Bool readmore) If req is NULL, the return
   value will be a pointer to the start of the complete request
   that follows the one currently being executed for the client.
   If req is not NULL, the function assumes that req is a pointer
   to a request in the client's request buffer, and the return
   value will be a pointer to the the start of the complete
   request that follows req. If the complete request is not
   available, the function returns NULL; pointers to partial
   requests will never be returned. If (and only if) readmore is
   TRUE, PeekNextRequest should try to read an additional request
   from the client if one is not already available in the client's
   request buffer. If PeekNextRequest reads more data into the
   request buffer, it should not move or change the existing data.
   void SkipRequests(xReqPtr req, ClientPtr client, int
   numskipped) The requests for the client up to and including the
   one specified by req will be skipped. numskipped must be the
   number of requests being skipped. Normal request processing
   will resume with the request that follows req. The caller must
   not have modified the contents of the request buffer in any way
   (e.g., by doing byte swapping in place). Additionally, two
   macros in os.h operate on the xReq pointer returned by
   PeekNextRequest: int ReqLen(xReqPtr req, ClientPtr client) The
   value of ReqLen is the request length in bytes of the given
   xReq. otherReqTypePtr CastxReq(xReq *req, otherReqTypePtr) The
   value of CastxReq is the conversion of the given request
   pointer to an otherReqTypePtr (which should be a pointer to a
   protocol structure type). Only those fields which come after
   the length field of otherReqType may be accessed via the
   returned pointer. Thus the first two fields of a request,
   reqType and data, can be accessed directly using the xReq *
   returned by PeekNextRequest. The next field, the length, can be
   accessed with ReqLen. Fields beyond that can be accessed with
   CastxReq. This complexity was necessary because of the
   reencoding of core protocol that can happen due to the
   BigRequests extension. DDX Layer This section describes the
   interface between DIX and DDX. While there may be an
   OS-dependent driver interface between DDX and the physical
   device, that interface is left to the DDX implementor and is
   not specified here. The DDX layer does most of its work through
   procedures that are pointed to by different structs. As
   previously described, the behavior of these resources is
   largely determined by these procedure pointers. Most of these
   routines are for graphic display on the screen or support
   functions thereof. The rest are for user input from input
   devices. Input In this document "input" refers to input from
   the user, such as mouse, keyboard, and bar code readers. X
   input devices are of several types: keyboard, pointing device,
   and many others. The core server has support for extension
   devices as described by the X Input Extension document; the
   interfaces used by that extension are described elsewhere. The
   core devices are actually implemented as two collections of
   devices, the mouse is a ButtonDevice, a ValuatorDevice and a
   PtrFeedbackDevice while the keyboard is a KeyDevice, a
   FocusDevice and a KbdFeedbackDevice. Each part implements a
   portion of the functionality of the device. This abstraction is
   hidden from view for core devices by DIX. You, the DDX
   programmer, are responsible for some of the routines in this
   section. Others are DIX routines that you should call to do the
   things you need to do in these DDX routines. Pay attention to
   which is which. Input Device Data Structures DIX keeps a global
   directory of devices in a central data structure called
   InputInfo. For each device there is a device structure called a
   DeviceRec. DIX can locate any DeviceRec through InputInfo. In
   addition, it has a special pointer to identify the main
   pointing device and a special pointer to identify the main
   keyboard. The DeviceRec (Xserver/include/input.h) is a
   device-independent structure that contains the state of an
   input device. A DevicePtr is simply a pointer to a DeviceRec.
   An xEvent describes an event the server reports to a client.
   Defined in Xproto.h, it is a huge struct of union of structs
   that have fields for all kinds of events. All of the variants
   overlap, so that the struct is actually very small in memory.
   Processing Events The main DDX input interface is the following
   routine: void ProcessInputEvents() You must write this routine
   to deliver input events from the user. DIX calls it when input
   is pending (see next section), and possibly even when it is
   not. You should write it to get events from each device and
   deliver the events to DIX. To deliver the events to DIX, DDX
   should call the following routine: void
   DevicePtr->processInputProc(pEvent, device, count) xEventPtr
   events; DeviceIntPtr device; int count; This is the "input
   proc" for the device, a DIX procedure. DIX will fill in this
   procedure pointer to one of its own routines by the time
   ProcessInputEvents() is called the first time. Call this input
   proc routine as many times as needed to deliver as many events
   as should be delivered. DIX will buffer them up and send them
   out as needed. Count is set to the number of event records
   which make up one atomic device event and is always 1 for the
   core devices (see the X Input Extension for descriptions of
   devices which may use count > 1). For example, your
   ProcessInputEvents() routine might check the mouse and the
   keyboard. If the keyboard had several keystrokes queued up, it
   could just call the keyboard's processInputProc as many times
   as needed to flush its internal queue. event is an xEvent
   struct you pass to the input proc. When the input proc returns,
   it is finished with the event rec, and you can fill in new
   values and call the input proc again with it. You should
   deliver the events in the same order that they were generated.
   For keyboard and pointing devices the xEvent variant should be
   keyButtonPointer. Fill in the following fields in the xEvent
   record: type - is one of the following: KeyPress, KeyRelease,
   ButtonPress, ButtonRelease, or MotionNotifydetail - for
   KeyPress or KeyRelease fields, this should be the key number
   (not the ASCII code); otherwise unusedtime - is the time that
   the event happened (32-bits, in milliseconds, arbitrary
   origin)rootX - is the x coordinate of cursorrootY - is the y
   coordinate of cursor The rest of the fields are filled in by
   DIX. The time stamp is maintained by your code in the DDX
   layer, and it is your responsibility to stamp all events
   correctly. The x and y coordinates of the pointing device and
   the time must be filled in for all event types including
   keyboard events. The pointing device must report all button
   press and release events. In addition, it should report a
   MotionNotify event every time it gets called if the pointing
   device has moved since the last notify. Intermediate pointing
   device moves are stored in a special GetMotionEvents buffer,
   because most client programs are not interested in them. There
   are quite a collection of sample implementations of this
   routine, one for each supported device. Telling DIX When Input
   is Pending In the server's dispatch loop, DIX checks to see if
   there is any device input pending whenever WaitForSomething()
   returns. If the check says that input is pending, DIX calls the
   DDX routine ProcessInputEvents(). This check for pending input
   must be very quick; a procedure call is too slow. The code that
   does the check is a hardwired IF statement in DIX code that
   simply compares the values pointed to by two pointers. If the
   values are different, then it assumes that input is pending and
   ProcessInputEvents() is called by DIX. You must pass pointers
   to DIX to tell it what values to compare. The following
   procedure is used to set these pointers: void SetInputCheck(p1,
   p2) long *p1, *p2; You should call it sometime during
   initialization to indicate to DIX the correct locations to
   check. You should pay special attention to the size of what
   they actually point to, because the locations are assumed to be
   longs. These two pointers are initialized by DIX to point to
   arbitrary values that are different. In other words, if you
   forget to call this routine during initialization, the worst
   thing that will happen is that ProcessInputEvents will be
   called when there are no events to process. p1 and p2 might
   point at the head and tail of some shared memory queue. Another
   use would be to have one point at a constant 0, with the other
   pointing at some mask containing 1s for each input device that
   has something pending. The DDX layer of the sample server calls
   SetInputCheck() once when the server's private internal queue
   is initialized. It passes pointers to the queue's head and
   tail. See Xserver/mi/mieq.c. int TimeSinceLastInputEvent() DDX
   must time stamp all hardware input events. But DIX sometimes
   needs to know the time and the OS layer needs to know the time
   since the last hardware input event in order for the screen
   saver to work. TimeSinceLastInputEvent() returns the this time
   in milliseconds. Controlling Input Devices You must write four
   routines to do various device-specific things with the keyboard
   and pointing device. They can have any name you wish because
   you pass the procedure pointers to DIX routines. int
   pInternalDevice->valuator->GetMotionProc(pdevice, coords,
   start, stop, pScreen) DeviceIntPtr pdevice; xTimecoord *
   coords; unsigned long start; unsigned long stop; ScreenPtr
   pScreen; You write this DDX routine to fill in coords with all
   the motion events that have times (32-bit count of
   milliseconds) between time start and time stop. It should
   return the number of motion events returned. If there is no
   motion events support, this routine should do nothing and
   return zero. The maximum number of coords to return is set in
   InitPointerDeviceStruct(), below. When the user drags the
   pointing device, the cursor position theoretically sweeps
   through an infinite number of points. Normally, a client that
   is concerned with points other than the starting and ending
   points will receive a pointer-move event only as often as the
   server generates them. (Move events do not queue up; each new
   one replaces the last in the queue.) A server, if desired, can
   implement a scheme to save these intermediate events in a
   motion buffer. A client application, like a paint program, may
   then request that these events be delivered to it through the
   GetMotionProc routine. void
   pInternalDevice->bell->BellProc(percent, pDevice, ctrl,
   unknown) int percent; DeviceIntPtr pDevice; pointer ctrl; int
   class; You need to write this routine to ring the bell on the
   keyboard. loud is a number from 0 to 100, with 100 being the
   loudest. Class is either BellFeedbackClass or KbdFeedbackClass
   (from XI.h). void pInternalDevice->somedevice->CtrlProc(device,
   ctrl) DevicePtr device; SomethingCtrl *ctrl; You write two
   versions of this procedure, one for the keyboard and one for
   the pointing device. DIX calls it to inform DDX when a client
   has requested changes in the current settings for the
   particular device. For a keyboard, this might be the repeat
   threshold and rate. For a pointing device, this might be a
   scaling factor (coarse or fine) for position reporting. See
   input.h for the ctrl structures. Input Initialization Input
   initialization is a bit complicated. It all starts with
   InitInput(), a routine that you write to call AddInputDevice()
   twice (once for pointing device and once for keyboard.) You
   also want to call RegisterKeyboardDevice() and
   RegisterPointerDevice() on them. When you Add the devices, a
   routine you supply for each device gets called to initialize
   them. Your individual initialize routines must call
   InitKeyboardDeviceStruct() or InitPointerDeviceStruct(),
   depending upon which it is. In other words, you indicate twice
   that the keyboard is the keyboard and the pointer is the
   pointer. void InitInput(argc, argv) int argc; char **argv;
   InitInput is a DDX routine you must write to initialize the
   input subsystem in DDX. It must call AddInputDevice() for each
   device that might generate events. In addition, you must
   register the main keyboard and pointing devices by calling
   RegisterPointerDevice() and RegisterKeyboardDevice(). DevicePtr
   AddInputDevice(deviceProc, autoStart) DeviceProc deviceProc;
   Bool autoStart; AddInputDevice is a DIX routine you call to
   create a device object. deviceProc is a DDX routine that is
   called by DIX to do various operations. AutoStart should be
   TRUE for devices that need to be turned on at initialization
   time with a special call, as opposed to waiting for some client
   application to turn them on. This routine returns NULL if
   sufficient memory cannot be allocated to install the device.
   Note also that except for the main keyboard and pointing
   device, an extension is needed to provide for a client
   interface to a device. void RegisterPointerDevice(device)
   DevicePtr device; RegisterPointerDevice is a DIX routine that
   your DDX code calls that makes that device the main pointing
   device. This routine is called once upon initialization and
   cannot be called again. void RegisterKeyboardDevice(device)
   DevicePtr device; RegisterKeyboardDevice makes the given device
   the main keyboard. This routine is called once upon
   initialization and cannot be called again. The following DIX
   procedures return the specified DevicePtr. They may or may not
   be useful to DDX implementors. DevicePtr LookupKeyboardDevice()
   LookupKeyboardDevice returns pointer for current main keyboard
   device. DevicePtr LookupPointerDevice() LookupPointerDevice
   returns pointer for current main pointing device. A DeviceProc
   (the kind passed to AddInputDevice()) in the following form:
   Bool pInternalDevice->DeviceProc(device, action); DeviceIntPtr
   device; int action; You must write a DeviceProc for each
   device. device points to the device record. action tells what
   action to take; it will be one of these defined constants
   (defined in input.h): DEVICE_INIT - At DEVICE_INIT time, the
   device should initialize itself by calling
   InitPointerDeviceStruct(), InitKeyboardDeviceStruct(), or a
   similar routine (see below) and "opening" the device if
   necessary. If you return a non-zero (i.e., != Success) value
   from the DEVICE_INIT call, that device will be considered
   unavailable. If either the main keyboard or main pointing
   device cannot be initialized, the DIX code will refuse to
   continue booting up. DEVICE_ON - If the DeviceProc is called
   with DEVICE_ON, then it is allowed to start putting events into
   the client stream by calling through the ProcessInputProc in
   the device. DEVICE_OFF - If the DeviceProc is called with
   DEVICE_OFF, no further events from that device should be given
   to the DIX layer. The device will appear to be dead to the
   user. DEVICE_CLOSE - At DEVICE_CLOSE (terminate or reset) time,
   the device should be totally closed down. void
   InitPointerDeviceStruct(device, map, mapLength,
   GetMotionEvents, ControlProc, numMotionEvents) DevicePtr
   device; CARD8 *map; int mapLength; ValuatorMotionProcPtr
   ControlProc; PtrCtrlProcPtr GetMotionEvents; int
   numMotionEvents; InitPointerDeviceStruct is a DIX routine you
   call at DEVICE_INIT time to declare some operating routines and
   data structures for a pointing device. map and mapLength are as
   described in the X Window System protocol specification.
   ControlProc and GetMotionEvents are DDX routines, see above.
   numMotionEvents is for the motion-buffer-size for the
   GetMotionEvents request. A typical length for a motion buffer
   would be 100 events. A server that does not implement this
   capability should set numMotionEvents to zero. void
   InitKeyboardDeviceStruct(device, pKeySyms, pModifiers, Bell,
   ControlProc) DevicePtr device; KeySymsPtr pKeySyms; CARD8
   *pModifiers; BellProcPtr Bell; KbdCtrlProcPtr ControlProc; You
   call this DIX routine when a keyboard device is initialized and
   its device procedure is called with DEVICE_INIT. The formats of
   the keysyms and modifier maps are defined in
   Xserver/include/input.h. They describe the layout of keys on
   the keyboards, and the glyphs associated with them. ( See the
   next section for information on setting up the modifier map and
   the keysym map.) ControlProc and Bell are DDX routines, see
   above. Keyboard Mapping and Keycodes When you send a keyboard
   event, you send a report that a given key has either been
   pressed or has been released. There must be a keycode for each
   key that identifies the key; the keycode-to-key mapping can be
   any mapping you desire, because you specify the mapping in a
   table you set up for DIX. However, you are restricted by the
   protocol specification to keycode values in the range 8 to 255
   inclusive. The keycode mapping information that you set up
   consists of the following: A minimum and maximum keycode number
   An array of sets of keysyms for each key, that is of length
   maxkeycode - minkeycode + 1. Each element of this array is a
   list of codes for symbols that are on that key. There is no
   limit to the number of symbols that can be on a key. Once the
   map is set up, DIX keeps and maintains the client's changes to
   it. The X protocol defines standard names to indicate the
   symbol(s) printed on each keycap. (See X11/keysym.h) Legal
   modifier keys must generate both up and down transitions. When
   a client tries to change a modifier key (for instance, to make
   "A" the "Control" key), DIX calls the following routine, which
   should retuurn TRUE if the key can be used as a modifier on the
   given device: Bool LegalModifier(key, pDev) unsigned int key;
   DevicePtr pDev; Screens Different computer graphics displays
   have different capabilities. Some are simple monochrome frame
   buffers that are just lying there in memory, waiting to be
   written into. Others are color displays with many bits per
   pixel using some color lookup table. Still others have
   high-speed graphic processors that prefer to do all of the work
   themselves, including maintaining their own high-level, graphic
   data structures. Screen Hardware Requirements The only
   requirement on screens is that you be able to both read and
   write locations in the frame buffer. All screens must have a
   depth of 32 or less (unless you use an X extension to allow a
   greater depth). All screens must fit into one of the classes
   listed in the section in this document on Visuals and Depths. X
   uses the pixel as its fundamental unit of distance on the
   screen. Therefore, most programs will measure everything in
   pixels. The sample server assumes square pixels. Serious
   WYSIWYG (what you see is what you get) applications for
   publishing and drawing programs will adjust for different
   screen resolutions automatically. Considerable work is involved
   in compensating for non-square pixels (a bit in the DDX code
   for the sample server but quite a bit in the client
   applications).Data Structures X supports multiple screens that
   are connected to the same server. Therefore, all the per-screen
   information is bundled into one data structure of attributes
   and procedures, which is the ScreenRec (see
   Xserver/include/scrnintstr.h). The procedure entry points in a
   ScreenRec operate on regions, colormaps, cursors, and fonts,
   because these resources can differ in format from one screen to
   another. Windows are areas on the screen that can be drawn into
   by graphic routines. "Pixmaps" are off-screen graphic areas
   that can be drawn into. They are both considered drawables and
   are described in the section on Drawables. All graphic
   operations work on drawables, and operations are available to
   copy patches from one drawable to another. The pixel image data
   in all drawables is in a format that is private to DDX. In
   fact, each instance of a drawable is associated with a given
   screen. Presumably, the pixel image data for pixmaps is chosen
   to be conveniently understood by the hardware. All screens in a
   single server must be able to handle all pixmaps depths
   declared in the connection setup information. Pixmap images are
   transferred to the server in one of two ways: XYPixmap or
   ZPimap. XYPixmaps are a series of bitmaps, one for each bit
   plane of the image, using the bitmap padding rules from the
   connection setup. ZPixmaps are a series of bits, nibbles, bytes
   or words, one for each pixel, using the format rules (padding
   and so on) for the appropriate depth. All screens in a given
   server must agree on a set of pixmap image formats
   (PixmapFormat) to support (depth, number of bits per pixel,
   etc.). There is no color interpretation of bits in the pixmap.
   Pixmaps do not contain pixel values. The interpretation is made
   only when the bits are transferred onto the screen. The
   screenInfo structure (in scrnintstr.h) is a global data
   structure that has a pointer to an array of ScreenRecs, one for
   each screen on the server. (These constitute the one and only
   description of each screen in the server.) Each screen has an
   identifying index (0, 1, 2, ...). In addition, the screenInfo
   struct contains global server-wide details, such as the bit-
   and byte- order in all bit images, and the list of pixmap image
   formats that are supported. The X protocol insists that these
   must be the same for all screens on the server.Output
   Initialization InitOutput(pScreenInfo, argc, argv) ScreenInfo
   *pScreenInfo; int argc; char **argv; Upon initialization, your
   DDX routine InitOutput() is called by DIX. It is passed a
   pointer to screenInfo to initialize. It is also passed the argc
   and argv from main() for your server for the command-line
   arguments. These arguments may indicate what or how many screen
   device(s) to use or in what way to use them. For instance, your
   server command line may allow a "-D" flag followed by the name
   of the screen device to use. Your InitOutput() routine should
   initialize each screen you wish to use by calling AddScreen(),
   and then it should initialize the pixmap formats that you
   support by storing values directly into the screenInfo data
   structure. You should also set certain implementation-dependent
   numbers and procedures in your screenInfo, which determines the
   pixmap and scanline padding rules for all screens in the
   server. int AddScreen(scrInitProc, argc, argv) Bool
   (*scrInitProc)(); int argc; char **argv; You should call
   AddScreen(), a DIX procedure, in InitOutput() once for each
   screen to add it to the screenInfo database. The first argument
   is an initialization procedure for the screen that you supply.
   The second and third are the argc and argv from main(). It
   returns the screen number of the screen installed, or -1 if
   there is either insufficient memory to add the screen, or
   (*scrInitProc) returned FALSE. The scrInitProc should be of the
   following form: Bool scrInitProc(iScreen, pScreen, argc, argv)
   int iScreen; ScreenPtr pScreen; int argc; char **argv; iScreen
   is the index for this screen; 0 for the first one initialized,
   1 for the second, etc. pScreen is the pointer to the screen's
   new ScreenRec. argc and argv are as before. Your screen
   initialize procedure should return TRUE upon success or FALSE
   if the screen cannot be initialized (for instance, if the
   screen hardware does not exist on this machine). This procedure
   must determine what actual device it is supposed to initialize.
   If you have a different procedure for each screen, then it is
   no problem. If you have the same procedure for multiple
   screens, it may have trouble figuring out which screen to
   initialize each time around, especially if InitOutput() does
   not initialize all of the screens. It is probably easiest to
   have one procedure for each screen. The initialization
   procedure should fill in all the screen procedures for that
   screen (windowing functions, region functions, etc.) and
   certain screen attributes for that screen.Region Routines in
   the ScreenRec A region is a dynamically allocated data
   structure that describes an irregularly shaped piece of real
   estate in XY pixel space. You can think of it as a set of
   pixels on the screen to be operated upon with set operations
   such as AND and OR. A region is frequently implemented as a
   list of rectangles or bitmaps that enclose the selected pixels.
   Region operators control the "clipping policy," or the
   operations that work on regions. (The sample server uses
   YX-banded rectangles. Unless you have something already
   implemented for your graphics system, you should keep that
   implementation.) The procedure pointers to the region operators
   are located in the ScreenRec data structure. The definition of
   a region can be found in the file Xserver/include/regionstr.h.
   The region code is found in Xserver/mi/miregion.c. DDX
   implementations using other region formats will need to supply
   different versions of the region operators. Since the list of
   rectangles is unbounded in size, part of the region data
   structure is usually a large, dynamically allocated chunk of
   memory. As your region operators calculate logical combinations
   of regions, these blocks may need to be reallocated by your
   region software. For instance, in the sample server, a
   RegionRec has some header information and a pointer to a
   dynamically allocated rectangle list. Periodically, the
   rectangle list needs to be expanded with Xrealloc(), whereupon
   the new pointer is remembered in the RegionRec. Most of the
   region operations come in two forms: a function pointer in the
   Screen structure, and a macro. The server can be compiled so
   that the macros make direct calls to the appropriate functions
   (instead of indirecting through a screen function pointer), or
   it can be compiled so that the macros are identical to the
   function pointer forms. Making direct calls is faster on many
   architectures. RegionPtr pScreen->RegionCreate( rect, size)
   BoxPtr rect; int size; macro: RegionPtr REGION_CREATE(pScreen,
   rect, size) RegionCreate creates a region that describes ONE
   rectangle. The caller can avoid unnecessary reallocation and
   copying by declaring the probable maximum number of rectangles
   that this region will need to describe itself. Your region
   routines, though, cannot fail just because the region grows
   beyond this size. The caller of this routine can pass almost
   anything as the size; the value is merely a good guess as to
   the maximum size until it is proven wrong by subsequent use.
   Your region procedures are then on their own in estimating how
   big the region will get. Your implementation might ignore size,
   if applicable. void pScreen->RegionInit (pRegion, rect, size)
   RegionPtr pRegion; BoxPtr rect; int size; macro:
   REGION_INIT(pScreen, pRegion, rect, size) Given an existing raw
   region structure (such as an local variable), this routine
   fills in the appropriate fields to make this region as usable
   as one returned from RegionCreate. This avoids the additional
   dynamic memory allocation overhead for the region structure
   itself. Bool pScreen->RegionCopy(dstrgn, srcrgn) RegionPtr
   dstrgn, srcrgn; macro: Bool REGION_COPY(pScreen, dstrgn,
   srcrgn) RegionCopy copies the description of one region,
   srcrgn, to another already-created region, dstrgn; returning
   TRUE if the copy succeeded, and FALSE otherwise. void
   pScreen->RegionDestroy( pRegion) RegionPtr pRegion; macro:
   REGION_DESTROY(pScreen, pRegion) RegionDestroy destroys a
   region and frees all allocated memory. void
   pScreen->RegionUninit (pRegion) RegionPtr pRegion; macro:
   REGION_UNINIT(pScreen, pRegion) Frees everything except the
   region structure itself, useful when the region was originally
   passed to RegionInit instead of received from RegionCreate.
   When this call returns, pRegion must not be reused until it has
   been RegionInit'ed again. Bool pScreen->Intersect(newReg, reg1,
   reg2) RegionPtr newReg, reg1, reg2; macro: Bool
   REGION_INTERSECT(pScreen, newReg, reg1, reg2) Bool
   pScreen->Union(newReg, reg1, reg2) RegionPtr newReg, reg1,
   reg2; macro: Bool REGION_UNION(pScreen, newReg, reg1, reg2)
   Bool pScreen->Subtract(newReg, regMinuend, regSubtrahend)
   RegionPtr newReg, regMinuend, regSubtrahend; macro: Bool
   REGION_UNION(pScreen, newReg, regMinuend, regSubtrahend) Bool
   pScreen->Inverse(newReg, pReg, pBox) RegionPtr newReg, pReg;
   BoxPtr pBox; macro: Bool REGION_INVERSE(pScreen, newReg, pReg,
   pBox) The above four calls all do basic logical operations on
   regions. They set the new region (which already exists) to
   describe the logical intersection, union, set difference, or
   inverse of the region(s) that were passed in. Your routines
   must be able to handle a situation where the newReg is the same
   region as one of the other region arguments. The subtract
   function removes the Subtrahend from the Minuend and puts the
   result in newReg. The inverse function returns a region that is
   the pBox minus the region passed in. (A true "inverse" would
   make a region that extends to infinity in all directions but
   has holes in the middle.) It is undefined for situations where
   the region extends beyond the box. Each routine must return the
   value TRUE for success. void pScreen->RegionReset(pRegion,
   pBox) RegionPtr pRegion; BoxPtr pBox; macro:
   REGION_RESET(pScreen, pRegion, pBox) RegionReset sets the
   region to describe one rectangle and reallocates it to a size
   of one rectangle, if applicable. void
   pScreen->TranslateRegion(pRegion, x, y) RegionPtr pRegion; int
   x, y; macro: REGION_TRANSLATE(pScreen, pRegion, x, y)
   TranslateRegion simply moves a region +x in the x direction and
   +y in the y direction. int pScreen->RectIn(pRegion, pBox)
   RegionPtr pRegion; BoxPtr pBox; macro: int
   RECT_IN_REGION(pScreen, pRegion, pBox) RectIn returns one of
   the defined constants rgnIN, rgnOUT, or rgnPART, depending upon
   whether the box is entirely inside the region, entirely outside
   of the region, or partly in and partly out of the region. These
   constants are defined in Xserver/include/region.h. Bool
   pScreen->PointInRegion(pRegion, x, y, pBox) RegionPtr pRegion;
   int x, y; BoxPtr pBox; macro: Bool POINT_IN_REGION(pScreen,
   pRegion, x, y, pBox) PointInRegion returns true if the point x,
   y is in the region. In addition, it fills the rectangle pBox
   with coordinates of a rectangle that is entirely inside of
   pRegion and encloses the point. In the mi implementation, it is
   the largest such rectangle. (Due to the sample server
   implementation, this comes cheaply.) This routine used by DIX
   when tracking the pointing device and deciding whether to
   report mouse events or change the cursor. For instance, DIX
   needs to change the cursor when it moves from one window to
   another. Due to overlapping windows, the shape to check may be
   irregular. A PointInRegion() call for every pointing device
   movement may be too expensive. The pBox is a kind of wake-up
   box; DIX need not call PointInRegion() again until the cursor
   wanders outside of the returned box. Bool
   pScreen->RegionNotEmpty(pRegion) RegionPtr pRegion; macro: Bool
   REGION_NOTEMPTY(pScreen, pRegion) RegionNotEmpty is a boolean
   function that returns true or false depending upon whether the
   region encloses any pixels. void pScreen->RegionEmpty(pRegion)
   RegionPtr pRegion; macro: REGION_EMPTY(pScreen, pRegion)
   RegionEmpty sets the region to be empty. BoxPtr
   pScreen->RegionExtents(pRegion) RegionPtr pRegion; macro:
   REGION_EXTENTS(pScreen, pRegion) RegionExtents returns a
   rectangle that is the smallest possible superset of the entire
   region. The caller will not modify this rectangle, so it can be
   the one in your region struct. Bool pScreen->RegionAppend
   (pDstRgn, pRegion) RegionPtr pDstRgn; RegionPtr pRegion; macro:
   Bool REGION_APPEND(pScreen, pDstRgn, pRegion) Bool
   pScreen->RegionValidate (pRegion, pOverlap) RegionPtr pRegion;
   Bool *pOverlap; macro: Bool REGION_VALIDATE(pScreen, pRegion,
   pOverlap) These functions provide an optimization for clip list
   generation and must be used in conjunction. The combined effect
   is to produce the union of a collection of regions, by using
   RegionAppend several times, and finally calling RegionValidate
   which takes the intermediate representation (which needn't be a
   valid region) and produces the desired union. pOverlap is set
   to TRUE if any of the original regions overlap; FALSE
   otherwise. RegionPtr pScreen->BitmapToRegion (pPixmap)
   PixmapPtr pPixmap; macro: RegionPtr BITMAP_TO_REGION(pScreen,
   pPixmap) Given a depth-1 pixmap, this routine must create a
   valid region which includes all the areas of the pixmap filled
   with 1's and excludes the areas filled with 0's. This routine
   returns NULL if out of memory. RegionPtr pScreen->RectsToRegion
   (nrects, pRects, ordering) int nrects; xRectangle *pRects; int
   ordering; macro: RegionPtr RECTS_TO_REGION(pScreen, nrects,
   pRects, ordering) Given a client-supplied list of rectangles,
   produces a region which includes the union of all the
   rectangles. Ordering may be used as a hint which describes how
   the rectangles are sorted. As the hint is provided by a client,
   it must not be required to be correct, but the results when it
   is not correct are not defined (core dump is not an option
   here). void
   pScreen->SendGraphicsExpose(client,pRegion,drawable,major,minor
   ) ClientPtr client; RegionPtr pRegion; XID drawable; int major;
   int minor; SendGraphicsExpose dispatches a list of
   GraphicsExposure events which span the region to the specified
   client. If the region is empty, or a NULL pointer, a NoExpose
   event is sent instead.Cursor Routines for a Screen A cursor is
   the visual form tied to the pointing device. The default cursor
   is an "X" shape, but the cursor can have any shape. When a
   client creates a window, it declares what shape the cursor will
   be when it strays into that window on the screen. For each
   possible shape the cursor assumes, there is a CursorRec data
   structure. This data structure contains a pointer to a
   CursorBits data structure which contains a bitmap for the image
   of the cursor and a bitmap for a mask behind the cursor, in
   addition, the CursorRec data structure contains foreground and
   background colors for the cursor. The CursorBits data structure
   is shared among multiple CursorRec structures which use the
   same font and glyph to describe both source and mask. The
   cursor image is applied to the screen by applying the mask
   first, clearing 1 bits in its form to the background color, and
   then overwriting on the source image, in the foreground color.
   (One bits of the source image that fall on top of zero bits of
   the mask image are undefined.) This way, a cursor can have
   transparent parts, and opaque parts in two colors. X allows any
   cursor size, but some hardware cursor schemes allow a maximum
   of N pixels by M pixels. Therefore, you are allowed to
   transform the cursor to a smaller size, but be sure to include
   the hot-spot. CursorBits in Xserver/include/cursorstr.h is a
   device-independent structure containing a device-independent
   representation of the bits for the source and mask. (This is
   possible because the bitmap representation is the same for all
   screens.) When a cursor is created, it is "realized" for each
   screen. At realization time, each screen has the chance to
   convert the bits into some other representation that may be
   more convenient (for instance, putting the cursor into
   off-screen memory) and set up its device-private area in either
   the CursorRec data structure or CursorBits data structure as
   appropriate to possibly point to whatever data structures are
   needed. It is more memory-conservative to share realizations by
   using the CursorBits private field, but this makes the
   assumption that the realization is independent of the colors
   used (which is typically true). For instance, the following are
   the device private entries for a particular screen and cursor:
   pCursor->devPriv[pScreen->myNum]
   pCursor->bits->devPriv[pScreen->myNum] This is done because the
   change from one cursor shape to another must be fast and
   responsive; the cursor image should be able to flutter as fast
   as the user moves it across the screen. You must implement the
   following routines for your hardware: Bool
   pScreen->RealizeCursor( pScr, pCurs) ScreenPtr pScr; CursorPtr
   pCurs; Bool pScreen->UnrealizeCursor( pScr, pCurs) ScreenPtr
   pScr; CursorPtr pCurs; RealizeCursor and UnrealizeCursor should
   realize (allocate and calculate all data needed) and unrealize
   (free the dynamically allocated data) a given cursor when DIX
   needs them. They are called whenever a device-independent
   cursor is created or destroyed. The source and mask bits
   pointed to by fields in pCurs are undefined for bits beyond the
   right edge of the cursor. This is so because the bits are in
   Bitmap format, which may have pad bits on the right edge. You
   should inhibit UnrealizeCursor() if the cursor is currently in
   use; this happens when the system is reset. Bool
   pScreen->DisplayCursor( pScr, pCurs) ScreenPtr pScr; CursorPtr
   pCurs; DisplayCursor should change the cursor on the given
   screen to the one passed in. It is called by DIX when the user
   moves the pointing device into a different window with a
   different cursor. The hotspot in the cursor should be aligned
   with the current cursor position. void pScreen->RecolorCursor(
   pScr, pCurs, displayed) ScreenPtr pScr; CursorPtr pCurs; Bool
   displayed; RecolorCursor notifies DDX that the colors in pCurs
   have changed and indicates whether this is the cursor currently
   being displayed. If it is, the cursor hardware state may have
   to be updated. Whether displayed or not, state created at
   RealizeCursor time may have to be updated. A generic version,
   miRecolorCursor, may be used that does an unrealize, a realize,
   and possibly a display (in micursor.c); however this constrains
   UnrealizeCursor and RealizeCursor to always return TRUE as no
   error indication is returned here. void
   pScreen->ConstrainCursor( pScr, pBox) ScreenPtr pScr; BoxPtr
   pBox; ConstrainCursor should cause the cursor to restrict its
   motion to the rectangle pBox. DIX code is capable of enforcing
   this constraint by forcefully moving the cursor if it strays
   out of the rectangle, but ConstrainCursor offers a way to send
   a hint to the driver or hardware if such support is available.
   This can prevent the cursor from wandering out of the box, then
   jumping back, as DIX forces it back. void
   pScreen->PointerNonInterestBox( pScr, pBox) ScreenPtr pScr;
   BoxPtr pBox; PointerNonInterestBox is DIX's way of telling the
   pointing device code not to report motion events while the
   cursor is inside a given rectangle on the given screen. It is
   optional and, if not implemented, it should do nothing. This
   routine is called only when the client has declared that it is
   not interested in motion events in a given window. The
   rectangle you get may be a subset of that window. It saves DIX
   code the time required to discard uninteresting mouse motion
   events. This is only a hint, which may speed performance.
   Nothing in DIX currently calls PointerNonInterestBox. void
   pScreen->CursorLimits( pScr, pCurs, pHotBox, pTopLeftBox)
   ScreenPtr pScr; CursorPtr pCurs; BoxPtr pHotBox; BoxPtr
   pTopLeftBox; /* return value */ CursorLimits should calculate
   the box that the cursor hot spot is physically capable of
   moving within, as a function of the screen pScr, the
   device-independent cursor pCurs, and a box that DIX
   hypothetically would want the hot spot confined within,
   pHotBox. This routine is for informing DIX only; it alters no
   state within DDX. Bool pScreen->SetCursorPosition( pScr, newx,
   newy, generateEvent) ScreenPtr pScr; int newx; int newy; Bool
   generateEvent; SetCursorPosition should artificially move the
   cursor as though the user had jerked the pointing device very
   quickly. This is called in response to the WarpPointer request
   from the client, and at other times. If generateEvent is True,
   the device should decide whether or not to call
   ProcessInputEvents() and then it must call
   DevicePtr->processInputProc. Its effects are, of course,
   limited in value for absolute pointing devices such as a
   tablet. void NewCurrentScreen(newScreen, x, y) ScreenPtr
   newScreen; int x,y; If your ddx provides some mechanism for the
   user to magically move the pointer between multiple screens,
   you need to inform DIX when this occurs. You should call
   NewCurrentScreen to accomplish this, specifying the new screen
   and the new x and y coordinates of the pointer on that
   screen.Visuals, Depths and Pixmap Formats for Screens The
   "depth" of a image is the number of bits that are used per
   pixel to display it. The "bits per pixel" of a pixmap image
   that is sent over the client byte stream is a number that is
   either 4, 8, 16, 24 or 32. It is the number of bits used per
   pixel in Z format. For instance, a pixmap image that has a
   depth of six is best sent in Z format as 8 bits per pixel. A
   "pixmap image format" or a "pixmap format" is a description of
   the format of a pixmap image as it is sent over the byte
   stream. For each depth available on a server, there is one and
   only one pixmap format. This pixmap image format gives the bits
   per pixel and the scanline padding unit. (For instance, are
   pixel rows padded to bytes, 16-bit words, or 32-bit words?) For
   each screen, you must decide upon what depth(s) it supports.
   You should only count the number of bits used for the actual
   image. Some displays store additional bits to indicate what
   window this pixel is in, how close this object is to a viewer,
   transparency, and other data; do not count these bits. A
   "display class" tells whether the display is monochrome or
   color, whether there is a lookup table, and how the lookup
   table works. A "visual" is a combination of depth, display
   class, and a description of how the pixel values result in a
   color on the screen. Each visual has a set of masks and offsets
   that are used to separate a pixel value into its red, green,
   and blue components and a count of the number of colormap
   entries. Some of these fields are only meaningful when the
   class dictates so. Each visual also has a screen ID telling
   which screen it is usable on. Note that the depth does not
   imply the number of map_entries; for instance, a display can
   have 8 bits per pixel but only 254 colormap entries for use by
   applications (the other two being reserved by hardware for the
   cursor). Each visual is identified by a 32-bit visual ID which
   the client uses to choose what visual is desired on a given
   window. Clients can be using more than one visual on the same
   screen at the same time. The class of a display describes how
   this translation takes place. There are three ways to do the
   translation. Pseudo - The pixel value, as a whole, is looked up
   in a table of length map_entries to determine the color to
   display. True - The pixel value is broken up into red, green,
   and blue fields, each of which are looked up in separate red,
   green, and blue lookup tables, each of length map_entries. Gray
   - The pixel value is looked up in a table of length map_entries
   to determine a gray level to display. In addition, the lookup
   table can be static (resulting colors are fixed for each pixel
   value) or dynamic (lookup entries are under control of the
   client program). This leads to a total of six classes: Static
   Gray - The pixel value (of however many bits) determines
   directly the level of gray that the pixel assumes. Gray Scale -
   The pixel value is fed through a lookup table to arrive at the
   level of gray to display for the given pixel. Static Color -
   The pixel value is fed through a fixed lookup table that yields
   the color to display for that pixel. PseudoColor - The whole
   pixel value is fed through a programmable lookup table that has
   one color (including red, green, and blue intensities) for each
   possible pixel value, and that color is displayed. True Color -
   Each pixel value consists of one or more bits that directly
   determine each primary color intensity after being fed through
   a fixed table. Direct Color - Each pixel value consists of one
   or more bits for each primary color. Each primary color value
   is individually looked up in a table for that primary color,
   yielding an intensity for that primary color. For each pixel,
   the red value is looked up in the red table, the green value in
   the green table, and the blue value in the blue table. Here are
   some examples: A simple monochrome 1 bit per pixel display is
   Static Gray. A display that has 2 bits per pixel for a choice
   between the colors of black, white, green and violet is Static
   Color. A display that has three bits per pixel, where each bit
   turns on or off one of the red, green or blue guns, is in the
   True Color class. If you take the last example and scramble the
   correspondence between pixel values and colors it becomes a
   Static Color display. A display has 8 bits per pixel. The 8
   bits select one entry out of 256 entries in a lookup table,
   each entry consisting of 24 bits (8bits each for red, green,
   and blue). The display can show any 256 of 16 million colors on
   the screen at once. This is a pseudocolor display. The client
   application gets to fill the lookup table in this class of
   display. Imagine the same hardware from the last example. Your
   server software allows the user, on the command line that
   starts up the server program, to fill the lookup table to his
   liking once and for all. From then on, the server software
   would not change the lookup table until it exits. For instance,
   the default might be a lookup table with a reasonable sample of
   colors from throughout the color space. But the user could
   specify that the table be filled with 256 steps of gray scale
   because he knew ahead of time he would be manipulating a lot of
   black-and-white scanned photographs and not very many color
   things. Clients would be presented with this unchangeable
   lookup table. Although the hardware qualifies as a PseudoColor
   display, the facade presented to the X client is that this is a
   Static Color display. You have to decide what kind of display
   you have or want to pretend you have. When you initialize the
   screen(s), this class value must be set in the VisualRec data
   structure along with other display characteristics like the
   depth and other numbers. The allowable DepthRec's and
   VisualRec's are pointed to by fields in the ScreenRec. These
   are set up when InitOutput() is called; you should Xalloc()
   appropriate blocks or use static variables initialized to the
   correct values.Colormaps for Screens A colormap is a
   device-independent mapping between pixel values and colors
   displayed on the screen. Different windows on the same screen
   can have different colormaps at the same time. At any given
   time, the most recently installed colormap(s) will be in use in
   the server so that its (their) windows' colors will be
   guaranteed to be correct. Other windows may be off-color.
   Although this may seem to be chaotic, in practice most clients
   use the default colormap for the screen. The default colormap
   for a screen is initialized when the screen is initialized. It
   always remains in existence and is not owned by any regular
   client. It is owned by client 0 (the server itself). Many
   clients will simply use this default colormap for their
   drawing. Depending upon the class of the screen, the entries in
   this colormap may be modifiable by client applications.Colormap
   Routines You need to implement the following routines to handle
   the device-dependent aspects of color maps. You will end up
   placing pointers to these procedures in your ScreenRec data
   structure(s). The sample server implementations of many of
   these routines are in both cfbcmap.c and mfbcmap.c; since mfb
   does not do very much with color, the cfb versions are
   typically more useful prototypes. Bool
   pScreen->CreateColormap(pColormap) ColormapPtr pColormap; This
   routine is called by the DIX CreateColormap routine after it
   has allocated all the data for the new colormap and just before
   it returns to the dispatcher. It is the DDX layer's chance to
   initialize the colormap, particularly if it is a static map.
   See the following section for more details on initializing
   colormaps. The routine returns FALSE if creation failed, such
   as due to memory limitations. Notice that the colormap has a
   devPriv field from which you can hang any colormap specific
   storage you need. Since each colormap might need special
   information, we attached the field to the colormap and not the
   visual. void pScreen->DestroyColormap(pColormap) ColormapPtr
   pColormap; This routine is called by the DIX FreeColormap
   routine after it has uninstalled the colormap and notified all
   interested parties, and before it has freed any of the colormap
   storage. It is the DDX layer's chance to free any data it added
   to the colormap. void pScreen->InstallColormap(pColormap)
   ColormapPtr pColormap; InstallColormap should fill a lookup
   table on the screen with which the colormap is associated with
   the colors in pColormap. If there is only one hardware lookup
   table for the screen, then all colors on the screen may change
   simultaneously. In the more general case of multiple hardware
   lookup tables, this may cause some other colormap to be
   uninstalled, meaning that windows that subscribed to the
   colormap that was uninstalled may end up being off-color. See
   the note, below, about uninstalling maps. void
   pScreen->UninstallColormap(pColormap) ColormapPtr pColormap;
   UninstallColormap should remove pColormap from screen
   pColormap->pScreen. Some other map, such as the default map if
   possible, should be installed in place of pColormap if
   applicable. If pColormap is the default map, do nothing. If any
   client has requested ColormapNotify events, the DDX layer must
   notify the client. (The routine WalkTree() is be used to find
   such windows. The DIX routines TellNoMap(), TellNewMap() and
   TellGainedMap() are provided to be used as the procedure
   parameter to WalkTree. These procedures are in
   Xserver/dix/colormap.c.) int
   pScreen->ListInstalledColormaps(pScreen, pCmapList) ScreenPtr
   pScreen; XID *pCmapList; ListInstalledColormaps fills the
   pCMapList in with the resource ids of the installed maps and
   returns a count of installed maps. pCmapList will point to an
   array of size MaxInstalledMaps that was allocated by the
   caller. void pScreen->StoreColors (pmap, ndef, pdefs)
   ColormapPtr pmap; int ndef; xColorItem *pdefs; StoreColors
   changes some of the entries in the colormap pmap. The number of
   entries to change are ndef, and pdefs points to the information
   describing what to change. Note that partial changes of entries
   in the colormap are allowed. Only the colors indicated in the
   flags field of each xColorItem need to be changed. However, all
   three color fields will be sent with the proper value for the
   benefit of screens that may not be able to set part of a
   colormap value. If the screen is a static class, this routine
   does nothing. The structure of colormap entries is nontrivial;
   see colormapst.h and the definition of xColorItem in Xproto.h
   for more details. void pScreen->ResolveColor(pRed, pGreen,
   pBlue, pVisual) unsigned short *pRed, *pGreen, *pBlue;
   VisualPtr pVisual; Given a requested color, ResolveColor
   returns the nearest color that this hardware is capable of
   displaying on this visual. In other words, this rounds off each
   value, in place, to the number of bits per primary color that
   your screen can use. Remember that each screen has one of these
   routines. The level of roundoff should be what you would expect
   from the value you put in the bits_per_rgb field of the
   pVisual. Each value is an unsigned value ranging from 0 to
   65535. The bits least likely to be used are the lowest ones.
   For example, if you had a pseudocolor display with any number
   of bits per pixel that had a lookup table supplying 6 bits for
   each color gun (a total of 256K different colors), you would
   round off each value to 6 bits. Please don't simply truncate
   these values to the upper 6 bits, scale the result so that the
   maximum value seen by the client will be 65535 for each
   primary. This makes color values more portable between
   different depth displays (a 6-bit truncated white will not look
   white on an 8-bit display).Initializing a Colormap When a
   client requests a new colormap and when the server creates the
   default colormap, the procedure CreateColormap in the DIX layer
   is invoked. That procedure allocates memory for the colormap
   and related storage such as the lists of which client owns
   which pixels. It then sets a bit, BeingCreated, in the flags
   field of the ColormapRec and calls the DDX layer's
   CreateColormap routine. This is your chance to initialize the
   colormap. If the colormap is static, which you can tell by
   looking at the class field, you will want to fill in each color
   cell to match the hardwares notion of the color for that pixel.
   If the colormap is the default for the screen, which you can
   tell by looking at the IsDefault bit in the flags field, you
   should allocate BlackPixel and WhitePixel to match the values
   you set in the pScreen structure. (Of course, you picked those
   values to begin with.) You can also wait and use AllocColor()
   to allocate blackPixel and whitePixel after the default
   colormap has been created. If the default colormap is static
   and you initialized it in pScreen->CreateColormap, then use can
   use AllocColor afterwards to choose pixel values with the
   closest rgb values to those desired for blackPixel and
   whitePixel. If the default colormap is dynamic and
   uninitialized, then the rgb values you request will be obeyed,
   and AllocColor will again choose pixel values for you. These
   pixel values can then be stored into the screen. There are two
   ways to fill in the colormap. The simplest way is to use the
   DIX function AllocColor. int AllocColor (pmap, pred, pgreen,
   pblue, pPix, client) ColormapPtr pmap; unsigned short *pred,
   *pgreen, *pblue; Pixel *pPix; int client; This takes three
   pointers to 16 bit color values and a pointer to a suggested
   pixel value. The pixel value is either an index into one
   colormap or a combination of three indices depending on the
   type of pmap. If your colormap starts out empty, and you don't
   deliberately pick the same value twice, you will always get
   your suggested pixel. The truly nervous could check that the
   value returned in *pPix is the one AllocColor was called with.
   If you don't care which pixel is used, or would like them
   sequentially allocated from entry 0, set *pPix to 0. This will
   find the first free pixel and use that. AllocColor will take
   care of all the bookkeeping and will call StoreColors to get
   the colormap rgb values initialized. The hardware colormap will
   be changed whenever this colormap is installed. If for some
   reason AllocColor doesn't do what you want, you can do your own
   bookkeeping and call StoreColors yourself. This is much more
   difficult and shouldn't be necessary for most devices.Fonts for
   Screens A font is a set of bitmaps that depict the symbols in a
   character set. Each font is for only one typeface in a given
   size, in other words, just one bitmap for each character.
   Parallel fonts may be available in a variety of sizes and
   variations, including "bold" and "italic." X supports fonts for
   8-bit and 16-bit character codes (for oriental languages that
   have more than 256 characters in the font). Glyphs are bitmaps
   for individual characters. The source comes with some useful
   font files in an ASCII, plain-text format that should be
   comprehensible on a wide variety of operating systems. The text
   format, referred to as BDF, is a slight extension of the
   current Adobe 2.1 Bitmap Distribution Format (Adobe Systems,
   Inc.). A short paper in PostScript format is included with the
   sample server that defines BDF. It includes helpful pictures,
   which is why it is done in PostScript and is not included in
   this document. Your implementation should include some sort of
   font compiler to read these files and generate binary files
   that are directly usable by your server implementation. The
   sample server comes with the source for a font compiler. It is
   important the font properties contained in the BDF files are
   preserved across any font compilation. In particular, copyright
   information cannot be casually tossed aside without legal
   ramifications. Other properties will be important to some
   sophisticated applications. All clients get font information
   from the server. Therefore, your server can support any fonts
   it wants to. It should probably support at least the fonts
   supplied with the X11 tape. In principle, you can convert fonts
   from other sources or dream up your own fonts for use on your
   server.Portable Compiled Format A font compiler is supplied
   with the sample server. It has compile-time switches to convert
   the BDF files into a portable binary form, called Portable
   Compiled Format or PCF. This allows for an arbitrary data
   format inside the file, and by describing the details of the
   format in the header of the file, any PCF file can be read by
   any PCF reading client. By selecting the format which matches
   the required internal format for your renderer, the PCF reader
   can avoid reformatting the data each time it is read in. The
   font compiler should be quite portable. The fonts included with
   the tape are stored in fonts/bdf. The font compiler is found in
   fonts/tools/bdftopcf.Font Realization Each screen configured
   into the server has an opportunity at font-load time to
   "realize" a font into some internal format if necessary. This
   happens every time the font is loaded into memory. A font
   (FontRec in Xserver/include/dixfontstr.h) is a
   device-independent structure containing a device-independent
   representation of the font. When a font is created, it is
   "realized" for each screen. At this point, the screen has the
   chance to convert the font into some other format. The DDX
   layer can also put information in the devPrivate storage. Bool
   pScreen->RealizeFont(pScr, pFont) ScreenPtr pScr; FontPtr
   pFont; Bool pScreen->UnrealizeFont(pScr, pFont) ScreenPtr pScr;
   FontPtr pFont; RealizeFont and UnrealizeFont should calculate
   and allocate these extra data structures and dispose of them
   when no longer needed. These are called in response to OpenFont
   and CloseFont requests from the client. The sample server
   implementation is in mfbfont.c (which does very little).Other
   Screen Routines You must supply several other screen-specific
   routines for your X server implementation. Some of these are
   described in other sections: GetImage() is described in the
   Drawing Primitives section. GetSpans() is described in the
   Pixblit routine section. Several window and pixmap manipulation
   procedures are described in the Window section under Drawables.
   The CreateGC() routine is described under Graphics Contexts.
   void pScreen->QueryBestSize(kind, pWidth, pHeight) int kind;
   unsigned short *pWidth, *pHeight; ScreenPtr pScreen;
   QueryBestSize() returns the best sizes for cursors, tiles, and
   stipples in response to client requests. kind is one of the
   defined constants CursorShape, TileShape, or StippleShape
   (defined in X.h). For CursorShape, return the maximum width and
   height for cursors that you can handle. For TileShape and
   StippleShape, start with the suggested values in pWidth and
   pHeight and modify them in place to be optimal values that are
   greater than or equal to the suggested values. The sample
   server implementation is in Xserver/mfb/mfbmisc.c.
   pScreen->SourceValidate(pDrawable, x, y, width, height)
   DrawablePtr pDrawable; int x, y, width, height; SourceValidate
   should be called by CopyArea/CopyPlane primitives when the
   source drawable is not the same as the destination, and the
   SourceValidate function pointer in the screen is non-null. If
   you know that you will never need SourceValidate, you can avoid
   this check. Currently, SourceValidate is used by the mi
   software cursor code to remove the cursor from the screen when
   the source rectangle overlaps the cursor position.
   x,y,width,height describe the source rectangle (source
   relative, that is) for the copy operation. Bool
   pScreen->SaveScreen(pScreen, on) ScreenPtr pScreen; int on;
   SaveScreen() is used for Screen Saver support (see
   WaitForSomething()). pScreen is the screen to save. Bool
   pScreen->CloseScreen(pScreen) ScreenPtr pScreen; When the
   server is reset, it calls this routine for each screen. Bool
   pScreen->CreateScreenResources(pScreen) ScreenPtr pScreen; If
   this routine is not NULL, it will be called once per screen per
   server initialization/reset after all modules have had a chance
   to register their devPrivates on all structures that support
   them (see the section on devPrivates below). If you need to
   create any resources that have dynamic devPrivates as part of
   your screen initialization, you should do so in this function
   instead of in the screen init function passed to AddScreen to
   guarantee that the resources have a complete set of
   devPrivates. This routine returns TRUE if successful.Drawables
   A drawable is a descriptor of a surface that graphics are drawn
   into, either a window on the screen or a pixmap in memory. Each
   drawable has a type, class, ScreenPtr for the screen it is
   associated with, depth, position, size, and serial number. The
   type is one of the defined constants DRAWABLE_PIXMAP,
   DRAWABLE_WINDOW and UNDRAWABLE_WINDOW. (An undrawable window is
   used for window class InputOnly.) The serial number is
   guaranteed to be unique across drawables, and is used in
   determining the validity of the clipping information in a GC.
   The screen selects the set of procedures used to manipulate and
   draw into the drawable. Position is used (currently) only by
   windows; pixmaps must set these fields to 0,0 as this reduces
   the amount of conditional code executed throughout the mi code.
   Size indicates the actual client-specified size of the
   drawable. There are, in fact, no other fields that a window
   drawable and pixmap drawable have in common besides those
   mentioned here. Both PixmapRecs and WindowRecs are structs that
   start with a drawable and continue on with more fields. Pixmaps
   have devPrivate pointers which usually point to the pixmap data
   but could conceivably be used for anything that DDX wants. Both
   windows and pixmaps have an array of devPrivates unions, one
   entry of which will probably be used for DDX specific data.
   Entries in this array are allocated using
   Allocate{Window|Pixmap}PrivateIndex() (see Wrappers and
   devPrivates below). This is done because different graphics
   hardware has different requirements for management; if the
   graphics is always handled by a processor with an independent
   address space, there is no point having a pointer to the bit
   image itself. The definition of a drawable and a pixmap can be
   found in the file Xserver/include/pixmapstr.h. The definition
   of a window can be found in the file
   Xserver/include/windowstr.h.Pixmaps A pixmap is a
   three-dimensional array of bits stored somewhere offscreen,
   rather than in the visible portion of the screen's display
   frame buffer. It can be used as a source or destination in
   graphics operations. There is no implied interpretation of the
   pixel values in a pixmap, because it has no associated visual
   or colormap. There is only a depth that indicates the number of
   significant bits per pixel. Also, there is no implied physical
   size for each pixel; all graphic units are in numbers of
   pixels. Therefore, a pixmap alone does not constitute a
   complete image; it represents only a rectangular array of pixel
   values. Note that the pixmap data structure is
   reference-counted. The server implementation is free to put the
   pixmap data anywhere it sees fit, according to its graphics
   hardware setup. Many implementations will simply have the data
   dynamically allocated in the server's address space. More
   sophisticated implementations may put the data in undisplayed
   framebuffer storage. In addition to dynamic devPrivates (see
   the section on devPrivates below), the pixmap data structure
   has two fields that are private to the device. Although you can
   use them for anything you want, they have intended purposes.
   devKind is intended to be a device specific indication of the
   pixmap location (host memory, off-screen, etc.). In the sample
   server, since all pixmaps are in memory, devKind stores the
   width of the pixmap in bitmap scanline units. devPrivate is
   probably a pointer to the bits in the pixmap. A bitmap is a
   pixmap that is one bit deep. PixmapPtr
   pScreen->CreatePixmap(pScreen, width, height, depth) ScreenPtr
   pScreen; int width, height, depth; This ScreenRec procedure
   must create a pixmap of the size requested. It must allocate a
   PixmapRec and fill in all of the fields. The reference count
   field must be set to 1. If width or height are zero, no space
   should be allocated for the pixmap data, and if the
   implementation is using the devPrivate field as a pointer to
   the pixmap data, it should be set to NULL. If successful, it
   returns a pointer to the new pixmap; if not, it returns NULL.
   See Xserver/mfb/mfbpixmap.c for the sample server
   implementation. Bool pScreen->DestroyPixmap(pPixmap) PixmapPtr
   pPixmap; This ScreenRec procedure must "destroy" a pixmap. It
   should decrement the reference count and, if zero, it must
   deallocate the PixmapRec and all attached devPrivate blocks. If
   successful, it returns TRUE. See Xserver/mfb/mfbpixmap.c for
   the sample server implementation. Bool
   pScreen->ModifyPixmapHeader(pPixmap, width, height, depth,
   bitsPerPixel, devKind, pPixData) PixmapPtr pPixmap; int width;
   int height; int depth; int bitsPerPixel; int devKind; pointer
   pPixData; This routine takes a pixmap header (the PixmapRec
   plus all the dynamic devPrivates) and initializes the fields of
   the PixmapRec to the parameters of the same name. pPixmap must
   have been created via pScreen->CreatePixmap with a zero width
   or height to avoid allocating space for the pixmap data.
   pPixData is assumed to be the pixmap data; it will be stored in
   an implementation-dependent place (usually
   pPixmap->devPrivate.ptr). This routine returns TRUE if
   successful. See Xserver/mi/miscrinit.c for the sample server
   implementation. PixmapPtr GetScratchPixmapHeader(pScreen,
   width, height, depth, bitsPerPixel, devKind, pPixData)
   ScreenPtr pScreen; int width; int height; int depth; int
   bitsPerPixel; int devKind; pointer pPixData; void
   FreeScratchPixmapHeader(pPixmap) PixmapPtr pPixmap; DDX should
   use these two DIX routines when it has a buffer of raw image
   data that it wants to manipulate as a pixmap temporarily,
   usually so that some other part of the server can be leveraged
   to perform some operation on the data. The data should be
   passed in pPixData, and will be stored in an
   implementation-dependent place (usually
   pPixmap->devPrivate.ptr). The other fields go into the
   corresponding PixmapRec fields. If successful,
   GetScratchPixmapHeader returns a valid PixmapPtr which can be
   used anywhere the server expects a pixmap, else it returns
   NULL. The pixmap should be released when no longer needed
   (usually within the same function that allocated it) with
   FreeScratchPixmapHeader.Windows A window is a visible, or
   potentially visible, rectangle on the screen. DIX windowing
   functions maintain an internal n-ary tree data structure, which
   represents the current relationships of the mapped windows.
   Windows that are contained in another window are children of
   that window and are clipped to the boundaries of the parent.
   The root window in the tree is the window for the entire
   screen. Sibling windows constitute a doubly-linked list; the
   parent window has a pointer to the head and tail of this list.
   Each child also has a pointer to its parent. The border of a
   window is drawn by a DDX procedure when DIX requests that it be
   drawn. The contents of the window is drawn by the client
   through requests to the server. Window painting is orchestrated
   through an expose event system. When a region is exposed, DIX
   generates an expose event, telling the client to repaint the
   window and passing the region that is the minimal area needed
   to be repainted. As a favor to clients, the server may retain
   the output to the hidden parts of windows in off-screen memory;
   this is called "backing store". When a part of such a window
   becomes exposed, it can quickly move pixels into place instead
   of triggering an expose event and waiting for a client on the
   other end of the network to respond. Even if the network
   response is insignificant, the time to intelligently paint a
   section of a window is usually more than the time to just copy
   already-painted sections. At best, the repainting involves
   blanking out the area to a background color, which will take
   about the same amount of time. In this way, backing store can
   dramatically increase the performance of window moves. On the
   other hand, backing store can be quite complex, because all
   graphics drawn to hidden areas must be intercepted and
   redirected to the off-screen window sections. Not only can this
   be complicated for the server programmer, but it can also
   impact window painting performance. The backing store
   implementation can choose, at any time, to forget pieces of
   backing that are written into, relying instead upon expose
   events to repaint for simplicity. In X, the decision to use the
   backing-store scheme is made by you, the server implementor. X
   provides hooks for implementing backing store, therefore the
   decision to use this strategy can be made on the fly. For
   example, you may use backing store only for certain windows
   that the user requests or you may use backing store until
   memory runs out, at which time you start dropping pieces of
   backing as needed to make more room. When a window operation is
   requested by the client, such as a window being created or
   moved, a new state is computed. During this transition, DIX
   informs DDX what rectangles in what windows are about to become
   obscured and what rectangles in what windows have become
   exposed. This provides a hook for the implementation of backing
   store. If DDX is unable to restore exposed regions, DIX
   generates expose events to the client. It is then the client's
   responsibility to paint the window parts that were exposed but
   not restored. If a window is resized, pixels sometimes need to
   be moved, depending upon the application. The client can
   request "Gravity" so that certain blocks of the window are
   moved as a result of a resize. For instance, if the window has
   controls or other items that always hang on the edge of the
   window, and that edge is moved as a result of the resize, then
   those pixels should be moved to avoid having the client repaint
   it. If the client needs to repaint it anyway, such an operation
   takes time, so it is desirable for the server to approximate
   the appearance of the window as best it can while waiting for
   the client to do it perfectly. Gravity is used for that, also.
   The window has several fields used in drawing operations:
   clipList - This region, in conjunction with the client clip
   region in the gc, is used to clip output. clipList has the
   window's children subtracted from it, in addition to pieces of
   sibling windows that overlap this window. To get the list with
   the children included (subwindow-mode is IncludeInferiors), the
   routine NotClippedByChildren(pWin) returns the unclipped
   region. borderClip is the region used by CopyWindow and
   includes the area of the window, its children, and the border,
   but with the overlapping areas of sibling children removed.
   Most of the other fields are for DIX use only.Window Procedures
   in the ScreenRec You should implement all of the following
   procedures and store pointers to them in the screen record. The
   device-independent portion of the server "owns" the window
   tree. However, clever hardware might want to know the
   relationship of mapped windows. There are pointers to
   procedures in the ScreenRec data structure that are called to
   give the hardware a chance to update its internal state. These
   are helpers and hints to DDX only; they do not change the
   window tree, which is only changed by DIX. Bool
   pScreen->CreateWindow(pWin) WindowPtr pWin; This routine is a
   hook for when DIX creates a window. It should fill in the
   "Window Procedures in the WindowRec" below and also allocate
   the devPrivate block for it. See Xserver/mfb/mfbwindow.c for
   the sample server implementation. Bool
   pScreen->DestroyWindow(pWin); WindowPtr pWin; This routine is a
   hook for when DIX destroys a window. It should deallocate the
   devPrivate block for it and any other blocks that need to be
   freed, besides doing other cleanup actions. See
   Xserver/mfb/mfbwindow.c for the sample server implementation.
   Bool pScreen->PositionWindow(pWin, x, y); WindowPtr pWin; int
   x, y; This routine is a hook for when DIX moves or resizes a
   window. It should do whatever private operations need to be
   done when a window is moved or resized. For instance, if DDX
   keeps a pixmap tile used for drawing the background or border,
   and it keeps the tile rotated such that it is longword aligned
   to longword locations in the frame buffer, then you should
   rotate your tiles here. The actual graphics involved in moving
   the pixels on the screen and drawing the border are handled by
   CopyWindow(), below. See Xserver/mfb/mfbwindow.c for the sample
   server implementation. Bool pScreen->RealizeWindow(pWin);
   WindowPtr pWin; Bool pScreen->UnrealizeWindow(pWin); WindowPtr
   pWin; These routines are hooks for when DIX maps (makes
   visible) and unmaps (makes invisible) a window. It should do
   whatever private operations need to be done when these happen,
   such as allocating or deallocating structures that are only
   needed for visible windows. RealizeWindow does NOT draw the
   window border, background or contents; UnrealizeWindow does NOT
   erase the window or generate exposure events for underlying
   windows; this is taken care of by DIX. DIX does, however, call
   PaintWindowBackground() and PaintWindowBorder() to perform some
   of these. Bool pScreen->ChangeWindowAttributes(pWin, vmask)
   WindowPtr pWin; unsigned long vmask; ChangeWindowAttributes is
   called whenever DIX changes window attributes, such as the
   size, front-to-back ordering, title, or anything of lesser
   severity that affects the window itself. The sample server
   implements this routine. It computes accelerators for quickly
   putting up background and border tiles. (See description of the
   set of routines stored in the WindowRec.) int
   pScreen->ValidateTree(pParent, pChild, kind) WindowPtr pParent,
   pChild; VTKind kind; ValidateTree calculates the clipping
   region for the parent window and all of its children. This
   routine must be provided. The sample server has a
   machine-independent version in Xserver/mi/mivaltree.c. This is
   a very difficult routine to replace. void
   pScreen->PostValidateTree(pParent, pChild, kind) WindowPtr
   pParent, pChild; VTKind kind; If this routine is not NULL, DIX
   calls it shortly after calling ValidateTree, passing it the
   same arguments. This is useful for managing multi-layered
   framebuffers. The sample server sets this to NULL. void
   pScreen->WindowExposures(pWin, pRegion, pBSRegion) WindowPtr
   pWin; RegionPtr pRegion; RegionPtr pBSRegion; The
   WindowExposures() routine paints the border and generates
   exposure events for the window. pRegion is an unoccluded region
   of the window, and pBSRegion is an occluded region that has
   backing store. Since exposure events include a rectangle
   describing what was exposed, this routine may have to send back
   a series of exposure events, one for each rectangle of the
   region. The count field in the expose event is a hint to the
   client as to the number of regions that are after this one.
   This routine must be provided. The sample server has a
   machine-independent version in Xserver/mi/miexpose.c. void
   pScreen->ClipNotify (pWin, dx, dy) WindowPtr pWin; int dx, dy;
   Whenever the cliplist for a window is changed, this function is
   called to perform whatever hardware manipulations might be
   necessary. When called, the clip list and border clip regions
   in the window are set to the new values. dx,dy are the distance
   that the window has been moved (if at all).Window Painting
   Procedures In addition to the procedures listed above, there
   are four routines which manipulate the actual window image
   directly. In the sample server, mi implementations will work
   for most purposes and mfb/cfb routines speed up situations,
   such as solid backgrounds/borders or tiles that are 8, 16 or 32
   pixels square. These three routines are used for systems that
   implement a backing-store scheme for it to know when to stash
   away areas of pixels and to restore or reposition them. void
   pScreen->ClearToBackground(pWin, x, y, w, h,
   generateExposures); WindowPtr pWin; int x, y, w, h; Bool
   generateExposures; This routine is called on a window in
   response to a ClearToBackground request from the client. This
   request has two different but related functions, depending upon
   generateExposures. If generateExposures is true, the client is
   declaring that the given rectangle on the window is incorrectly
   painted and needs to be repainted. The sample server
   implementation calculates the exposure region and hands it to
   the DIX procedure HandleExposures(), which calls the
   WindowExposures() routine, below, for the window and all of its
   child windows. If generateExposures is false, the client is
   trying to simply erase part of the window to the background
   fill style. ClearToBackground should write the background color
   or tile to the rectangle in question (probably using
   PaintWindowBackground). If w or h is zero, it clears all the
   way to the right or lower edge of the window. The sample server
   implementation is in Xserver/mi/miwindow.c. void
   pScreen->PaintWindowBackground(pWin, region, kind) WindowPtr
   pWin; RegionPtr region; int kind; /* must be PW_BACKGROUND */
   void pScreen->PaintWindowBorder(pWin, region, kind) WindowPtr
   pWin; RegionPtr region; int kind; /* must be PW_BORDER */ These
   two routines are for painting pieces of the window background
   or border. They both actually paint the area designated by
   region. The kind parameter is a defined constant that is always
   PW_BACKGROUND or PW_BORDER, as shown. Therefore, you can use
   the same routine for both. The defined constant tells the
   routine whether to use the window's border fill style or its
   background fill style to paint the given region. Both fill
   styles consist of a union which holds a tile pointer and a
   pixel value, along with a separate variable which indicates
   which entry is valid. For PW_BORDER, borderIsPixel != 0
   indicates that the border PixUnion contains a pixel value, else
   a tile. For PW_BACKGROUND there are four values, contained in
   backgroundState; None, ParentRelative, BackgroundPixmap and
   BackgroundPixel. None indicates that the region should be left
   unfilled, while ParentRelative indicates that the background of
   the parent is inherited (see the Protocol document for the
   exact semantics). void pScreen->CopyWindow(pWin, oldpt,
   oldRegion); WindowPtr pWin; DDXPointRec oldpt; RegionPtr
   oldRegion; CopyWindow is called when a window is moved, and
   graphically moves to pixels of a window on the screen. It
   should not change any other state within DDX (see
   PositionWindow(), above). oldpt is the old location of the
   upper-left corner. oldRegion is the old region it is coming
   from. The new location and new region is stored in the
   WindowRec. oldRegion might modified in place by this routine
   (the sample implementation does this). CopyArea could be used,
   except that this operation has more complications. First of
   all, you do not want to copy a rectangle onto a rectangle. The
   original window may be obscured by other windows, and the new
   window location may be similarly obscured. Second, some
   hardware supports multiple windows with multiple depths, and
   your routine needs to take care of that. The pixels in
   oldRegion (with reference point oldpt) are copied to the
   window's new region (pWin->borderClip). pWin->borderClip is
   gotten directly from the window, rather than passing it as a
   parameter. The sample server implementation is in
   Xserver/mfb/mfbwindow.c.Screen Operations for Backing Store
   Each ScreenRec has six functions which provide the backing
   store interface. For screens not supporting backing store,
   these pointers may be nul. Servers that implement some backing
   store scheme must fill in the procedure pointers for the
   procedures below, and must maintain the backStorage field in
   each window struct. The sample implementation is in
   mi/mibstore.c. void pScreen->SaveDoomedAreas(pWin, pRegion, dx,
   dy) WindowPtr pWin; RegionPtr pRegion; int dx, dy; This routine
   saves the newly obscured region, pRegion, in backing store. dx,
   dy indicate how far the window is being moved, useful as the
   obscured region is relative to the window as it will appear in
   the new location, rather then relative to the bits as the are
   on the screen when the function is invoked. RegionPtr
   pScreen->RestoreAreas(pWin, pRegion) WindowPtr pWin; RegionPtr
   pRegion; This looks at the exposed region of the window,
   pRegion, and tries to restore to the screen the parts that have
   been saved. It removes the restored parts from the backing
   storage (because they are now on the screen) and subtracts the
   areas from the exposed region. The returned region is the area
   of the window which should have expose events generated for and
   can be either a new region, pWin->exposed, or NULL. The region
   left in pRegion is set to the area of the window which should
   be painted with the window background. RegionPtr
   pScreen->TranslateBackingStore(pWin, dx, dy, oldClip, oldx,
   oldy) WindowPtr pWin; int dx, dy; RegionPtr oldClip; int oldx,
   oldy; This is called when the window is moved or resized so
   that the backing store can be translated if necessary. oldClip
   is the old cliplist for the window, which is used to save
   doomed areas if the window is moved underneath its parent as a
   result of bitgravity. The returned region represents occluded
   areas of the window for which the backing store contents are
   invalid. void pScreen->ExposeCopy(pSrc, pDst, pGC, prgnExposed,
   srcx, srcy, dstx, dsty, plane) WindowPtr pSrc; DrawablePtr
   pDst; GCPtr pGC; RegionPtr prgnExposed; int srcx; int srcy; int
   dstx; int dsty; unsigned long plane; Copies a region from the
   backing store of pSrc to pDs. RegionPtr
   pScreen->ClearBackingStore(pWindow, x, y, w, h,
   generateExposures) WindowPtr pWindow; int x; int y; int w; int
   h; Bool generateExposures; Clear the given area of the backing
   pixmap with the background of the window. If generateExposures
   is TRUE, generate exposure events for the area. Note that if
   the area has any part outside the saved portions of the window,
   we do not allow the count in the expose events to be 0, since
   there will be more expose events to come. void
   pScreen->DrawGuarantee(pWindow, pGC, guarantee) WindowPtr
   pWindow; GCPtr pGC; int guarantee; This informs the backing
   store layer that you are about to validate a gc with a window,
   and that subsequent output to the window is (or is not)
   guaranteed to be already clipped to the visible regions of the
   window.Screen Operations for Multi-Layered Framebuffers The
   following screen functions are useful if you have a framebuffer
   with multiple sets of independent bit planes, e.g. overlays or
   underlays in addition to the "main" planes. If you have a
   simple single-layer framebuffer, you should probably use the mi
   versions of these routines in mi/miwindow.c. This can be easily
   accomplished by calling miScreenInit. void
   pScreen->MarkWindow(pWin) WindowPtr pWin; This formerly dix
   function MarkWindow has moved to ddx and is accessed via this
   screen function. This function should store something, usually
   a pointer to a device-dependent structure, in pWin->valdata so
   that ValidateTree has the information it needs to validate the
   window. Bool pScreen->MarkOverlappedWindows(parent, firstChild,
   ppLayerWin) WindowPtr parent; WindowPtr firstChild; WindowPtr *
   ppLayerWin; This formerly dix function MarkWindow has moved to
   ddx and is accessed via this screen function. In the process,
   it has grown another parameter: ppLayerWin, which is filled in
   with a pointer to the window at which save under marking and
   ValidateTree should begin. In the single-layered framebuffer
   case, pLayerWin == pWin. Bool
   pScreen->ChangeSaveUnder(pLayerWin, firstChild) WindowPtr
   pLayerWin; WindowPtr firstChild; The dix functions
   ChangeSaveUnder and CheckSaveUnder have moved to ddx and are
   accessed via this screen function. pLayerWin should be the
   window returned in the ppLayerWin parameter of
   MarkOverlappedWindows. The function may turn on backing store
   for windows that might be covered, and may partially turn off
   backing store for windows. It returns TRUE if
   PostChangeSaveUnder needs to be called to finish turning off
   backing store. void pScreen->PostChangeSaveUnder(pLayerWin,
   firstChild) WindowPtr pLayerWin; WindowPtr firstChild; The dix
   function DoChangeSaveUnder has moved to ddx and is accessed via
   this screen function. This function completes the job of
   turning off backing store that was started by ChangeSaveUnder.
   void pScreen->MoveWindow(pWin, x, y, pSib, kind) WindowPtr
   pWin; int x; int y; WindowPtr pSib; VTKind kind; The formerly
   dix function MoveWindow has moved to ddx and is accessed via
   this screen function. The new position of the window is given
   by x,y. kind is VTMove if the window is only moving, or VTOther
   if the border is also changing. void
   pScreen->ResizeWindow(pWin, x, y, w, h, pSib) WindowPtr pWin;
   int x; int y; unsigned int w; unsigned int h; WindowPtr pSib;
   The formerly dix function SlideAndSizeWindow has moved to ddx
   and is accessed via this screen function. The new position is
   given by x,y. The new size is given by w,h. WindowPtr
   pScreen->GetLayerWindow(pWin) WindowPtr pWin This is a new
   function which returns a child of the layer parent of pWin.
   void pScreen->HandleExposures(pWin) WindowPtr pWin; The
   formerly dix function HandleExposures has moved to ddx and is
   accessed via this screen function. This function is called
   after ValidateTree and uses the information contained in
   valdata to send exposures to windows. void
   pScreen->ReparentWindow(pWin, pPriorParent) WindowPtr pWin;
   WindowPtr pPriorParent; This function will be called when a
   window is reparented. At the time of the call, pWin will
   already be spliced into its new position in the window tree,
   and pPriorParent is its previous parent. This function can be
   NULL. void pScreen->SetShape(pWin) WindowPtr pWin; The formerly
   dix function SetShape has moved to ddx and is accessed via this
   screen function. The window's new shape will have already been
   stored in the window when this function is called. void
   pScreen->ChangeBorderWidth(pWin, width) WindowPtr pWin;
   unsigned int width; The formerly dix function ChangeBorderWidth
   has moved to ddx and is accessed via this screen function. The
   new border width is given by width. void
   pScreen->MarkUnrealizedWindow(pChild, pWin, fromConfigure)
   WindowPtr pChild; WindowPtr pWin; Bool fromConfigure; This
   function is called for windows that are being unrealized as
   part of an UnrealizeTree. pChild is the window being
   unrealized, pWin is an ancestor, and the fromConfigure value is
   simply propogated from UnrealizeTree.Graphics Contexts and
   Validation This graphics context (GC) contains state variables
   such as foreground and background pixel value (color), the
   current line style and width, the current tile or stipple for
   pattern generation, the current font for text generation, and
   other similar attributes. In many graphics systems, the
   equivalent of the graphics context and the drawable are
   combined as one entity. The main distinction between the two
   kinds of status is that a drawable describes a writing surface
   and the writings that may have already been done on it, whereas
   a graphics context describes the drawing process. A drawable is
   like a chalkboard. A GC is like a piece of chalk. Unlike many
   similar systems, there is no "current pen location." Every
   graphic operation is accompanied by the coordinates where it is
   to happen. The GC also includes two vectors of procedure
   pointers, the first operate on the GC itself and are called GC
   funcs. The second, called GC ops, contains the functions that
   carry out the fundamental graphic operations such as drawing
   lines, polygons, arcs, text, and copying bitmaps. The DDX
   graphic software can, if it wants to be smart, change these two
   vectors of procedure pointers to take advantage of
   hardware/firmware in the server machine, which can do a better
   job under certain circumstances. To reduce the amount of memory
   consumed by each GC, it is wise to create a few "boilerplate"
   GC ops vectors which can be shared by every GC which matches
   the constraints for that set. Also, it is usually reasonable to
   have every GC created by a particular module to share a common
   set of GC funcs. Samples of this sort of sharing can be seen in
   cfb/cfbgc.c and mfb/mfbgc.c. The DDX software is notified any
   time the client (or DIX) uses a changed GC. For instance, if
   the hardware has special support for drawing fixed-width fonts,
   DDX can intercept changes to the current font in a GC just
   before drawing is done. It can plug into either a fixed-width
   procedure that makes the hardware draw characters, or a
   variable-width procedure that carefully lays out glyphs by hand
   in software, depending upon the new font that is selected. A
   definition of these structures can be found in the file
   Xserver/include/gcstruct.h. Also included in each GC is an
   array of devPrivates which portions of the DDX can use for any
   reason. Entries in this array are allocated with
   AllocateGCPrivateIndex() (see Wrappers and Privates below). The
   DIX routines available for manipulating GCs are CreateGC,
   ChangeGC, CopyGC, SetClipRects, SetDashes, and FreeGC. GCPtr
   CreateGC(pDrawable, mask, pval, pStatus) DrawablePtr pDrawable;
   BITS32 mask; XID *pval; int *pStatus; int ChangeGC(pGC, mask,
   pval) GCPtr pGC; BITS32 mask; XID *pval; int CopyGC(pgcSrc,
   pgcDst, mask) GCPtr pgcSrc; GCPtr pgcDst; BITS32 mask; int
   SetClipRects(pGC, xOrigin, yOrigin, nrects, prects, ordering)
   GCPtr pGC; int xOrigin, yOrigin; int nrects; xRectangle
   *prects; int ordering; SetDashes(pGC, offset, ndash, pdash)
   GCPtr pGC; unsigned offset; unsigned ndash; unsigned char
   *pdash; int FreeGC(pGC, gid) GCPtr pGC; GContext gid; As a
   convenience, each Screen structure contains an array of GCs
   that are preallocated, one at each depth the screen supports.
   These are particularly useful in the mi code. Two DIX routines
   must be used to get these GCs: GCPtr GetScratchGC(depth,
   pScreen) int depth; ScreenPtr pScreen; FreeScratchGC(pGC) GCPtr
   pGC; Always use these two routines, don't try to extract the
   scratch GC yourself -- someone else might be using it, so a new
   one must be created on the fly. If you need a GC for a very
   long time, say until the server is restarted, you should not
   take one from the pool used by GetScratchGC, but should get
   your own using CreateGC or CreateScratchGC. This leaves the
   ones in the pool free for routines that only need it for a
   little while and don't want to pay a heavy cost to get it.
   GCPtr CreateScratchGC(pScreen, depth) ScreenPtr pScreen; int
   depth; NULL is returned if the GC cannot be created. The GC
   returned can be freed with FreeScratchGC.Details of Operation
   At screen initialization, a screen must supply a GC creation
   procedure. At GC creation, the screen must fill in GC funcs and
   GC ops vectors (Xserver/include/gcstruct.h). For any particular
   GC, the func vector must remain constant, while the op vector
   may vary. This invariant is to ensure that Wrappers work
   correctly. When a client request is processed that results in a
   change to the GC, the device-independent state of the GC is
   updated. This includes a record of the state that changed. Then
   the ChangeGC GC func is called. This is useful for graphics
   subsystems that are able to process state changes in parallel
   with the server CPU. DDX may opt not to take any action at
   GC-modify time. This is more efficient if multiple GC-modify
   requests occur between draws using a given GC. Validation
   occurs at the first draw operation that specifies the GC after
   that GC was modified. DIX calls then the ValidateGC GC func.
   DDX should then update its internal state. DDX internal state
   may be stored as one or more of the following: 1) device
   private block on the GC; 2) hardware state; 3) changes to the
   GC ops. The GC contains a serial number, which is loaded with a
   number fetched from the window that was drawn into the last
   time the GC was used. The serial number in the drawable is
   changed when the drawable's clipList or absCorner changes.
   Thus, by comparing the GC serial number with the drawable
   serial number, DIX can force a validate if the drawable has
   been changed since the last time it was used with this GC. In
   addition, the drawable serial number is always guaranteed to
   have the most significant bit set to 0. Thus, the DDX layer can
   set the most significant bit of the serial number to 1 in a GC
   to force a validate the next time the GC is used. DIX also uses
   this technique to indicate that a change has been made to the
   GC by way of a SetGC, a SetDashes or a SetClip request.GC
   Handling Routines The ScreenRec data structure has a pointer
   for CreateGC(). Bool pScreen->CreateGC(pGC) GCPtr pGC; This
   routine must fill in the fields of a dynamically allocated GC
   that is passed in. It does NOT allocate the GC record itself or
   fill in the defaults; DIX does that. This must fill in both the
   GC funcs and ops; none of the drawing functions will be called
   before the GC has been validated, but the others (dealing with
   allocating of clip regions, changing and destroying the GC,
   etc.) might be. The GC funcs vector contains pointers to 7
   routines and a devPrivate field: pGC->funcs->ChangeGC(pGC,
   changes) GCPtr pGC; unsigned long changes; This GC func is
   called immediately after a field in the GC is changed. changes
   is a bit mask indicating the changed fields of the GC in this
   request. The ChangeGC routine is useful if you have a system
   where state-changes to the GC can be swallowed immediately by
   your graphics system, and a validate is not necessary.
   pGC->funcs->ValidateGC(pGC, changes, pDraw) GCPtr pGC; unsigned
   long changes; DrawablePtr pDraw; ValidateGC is called by DIX
   just before the GC will be used when one of many possible
   changes to the GC or the graphics system has happened. It can
   modify a devPrivates field of the GC or its contents, change
   the op vector, or change hardware according to the values in
   the GC. It may not change the device-independent portion of the
   GC itself. In almost all cases, your ValidateGC() procedure
   should take the regions that drawing needs to be clipped to and
   combine them into a composite clip region, which you keep a
   pointer to in the private part of the GC. In this way, your
   drawing primitive routines (and whatever is below them) can
   easily determine what to clip and where. You should combine the
   regions clientClip (the region that the client desires to clip
   output to) and the region returned by NotClippedByChildren(),
   in DIX. An example is in Xserver/mfb/mfbgc.c. Some kinds of
   extension software may cause this routine to be called more
   than originally intended; you should not rely on algorithms
   that will break under such circumstances. See the Strategies
   document for more information on creatively using this routine.
   pGC->funcs->CopyGC(pGCSrc, mask, pGCDst) GCPtr pGCSrc; unsigned
   long mask; GCPtr pGCDst; This routine is called by DIX when a
   GC is being copied to another GC. This is for situations where
   dynamically allocated chunks of memory are hanging off a GC
   devPrivates field which need to be transferred to the
   destination GC. pGC->funcs->DestroyGC(pGC) GCPtr pGC; This
   routine is called before the GC is destroyed for the entity
   interested in this GC to clean up after itself. This routine is
   responsible for freeing any auxiliary storage allocated.GC Clip
   Region Routines The GC clientClip field requires three
   procedures to manage it. These procedures are in the GC funcs
   vector. The underlying principle is that dix knows nothing
   about the internals of the clipping information, (except when
   it has come from the client), and so calls ddX whenever it
   needs to copy, set, or destroy such information. It could have
   been possible for dix not to allow ddX to touch the field in
   the GC, and require it to keep its own copy in devPriv, but
   since clip masks can be very large, this seems like a bad idea.
   Thus, the server allows ddX to do whatever it wants to the
   clientClip field of the GC, but requires it to do all
   manipulation itself. void pGC->funcs->ChangeClip(pGC, type,
   pValue, nrects) GCPtr pGC; int type; char *pValue; int nrects;
   This routine is called whenever the client changes the client
   clip region. The pGC points to the GC involved, the type tells
   what form the region has been sent in. If type is CT_NONE, then
   there is no client clip. If type is CT_UNSORTED, CT_YBANDED or
   CT_YXBANDED, then pValue pointer to a list of rectangles,
   nrects long. If type is CT_REGION, then pValue pointer to a
   RegionRec from the mi region code. If type is CT_PIXMAP pValue
   is a pointer to a pixmap. (The defines for CT_NONE, etc. are in
   Xserver/include/gc.h.) This routine is responsible for
   incrementing any necessary reference counts (e.g. for a pixmap
   clip mask) for the new clipmask and freeing anything that used
   to be in the GC's clipMask field. The lists of rectangles
   passed in can be freed with Xfree(), the regions can be
   destroyed with the RegionDestroy field in the screen, and
   pixmaps can be destroyed by calling the screen's DestroyPixmap
   function. DIX and MI code expect what they pass in to this to
   be freed or otherwise inaccessible, and will never look inside
   what's been put in the GC. This is a good place to be wary of
   storage leaks. In the sample server, this routine transforms
   either the bitmap or the rectangle list into a region, so that
   future routines will have a more predictable starting point to
   work from. (The validate routine must take this client clip
   region and merge it with other regions to arrive at a composite
   clip region before any drawing is done.) void
   pGC->funcs->DestroyClip(pGC) GCPtr pGC; This routine is called
   whenever the client clip region must be destroyed. The pGC
   points to the GC involved. This call should set the clipType
   field of the GC to CT_NONE. In the sample server, the pointer
   to the client clip region is set to NULL by this routine after
   destroying the region, so that other software (including
   ChangeClip() above) will recognize that there is no client clip
   region. void pGC->funcs->CopyClip(pgcDst, pgcSrc) GCPtr pgcDst,
   pgcSrc; This routine makes a copy of the clipMask and clipType
   from pgcSrc into pgcDst. It is responsible for destroying any
   previous clipMask in pgcDst. The clip mask in the source can be
   the same as the clip mask in the dst (clients do the strangest
   things), so care must be taken when destroying things. This
   call is required because dix does not know how to copy the clip
   mask from pgcSrc.Drawing Primitives The X protocol (rules for
   the byte stream that goes between client and server) does all
   graphics using primitive operations, which are called Drawing
   Primitives. These include line drawing, area filling, arcs, and
   text drawing. Your implementation must supply 16 routines to
   perform these on your hardware. (The number 16 is arbitrary.)
   More specifically, 16 procedure pointers are in each GC op
   vector. At any given time, ALL of them MUST point to a valid
   procedure that attempts to do the operation assigned, although
   the procedure pointers may change and may point to different
   procedures to carry out the same operation. A simple server
   will leave them all pointing to the same 16 routines, while a
   more optimized implementation will switch each from one
   procedure to another, depending upon what is most optimal for
   the current GC and drawable. The sample server contains a
   considerable chunk of code called the mi (machine independent)
   routines, which serve as drawing primitive routines. Many
   server implementations will be able to use these as-is, because
   they work for arbitrary depths. They make no assumptions about
   the formats of pixmaps and frame buffers, since they call a set
   of routines known as the "Pixblit Routines" (see next section).
   They do assume that the way to draw is through these low-level
   routines that apply pixel values rows at a time. If your
   hardware or firmware gives more performance when things are
   done differently, you will want to take this fact into account
   and rewrite some or all of the drawing primitives to fit your
   needs.GC Components This section describes the fields in the GC
   that affect each drawing primitive. The only primitive that is
   not affected is GetImage, which does not use a GC because its
   destination is a protocol-style bit image. Since each drawing
   primitive mirrors exactly the X protocol request of the same
   name, you should refer to the X protocol specification document
   for more details. ALL of these routines MUST CLIP to the
   appropriate regions in the drawable. Since there are many
   regions to clip to simultaneously, your ValidateGC routine
   should combine these into a unified clip region to which your
   drawing routines can quickly refer. This is exactly what the
   cfb and mfb routines supplied with the sample server do. The mi
   implementation passes responsibility for clipping while drawing
   down to the Pixblit routines. Also, all of them must adhere to
   the current plane mask. The plane mask has one bit for every
   bit plane in the drawable; only planes with 1 bits in the mask
   are affected by any drawing operation. All functions except for
   ImageText calls must obey the alu function. This is usually
   Copy, but could be any of the allowable 16 raster-ops. All of
   the functions, except for CopyArea, might use the current
   foreground and background pixel values. Each pixel value is 32
   bits. These correspond to foreground and background colors, but
   you have to run them through the colormap to find out what
   color the pixel values represent. Do not worry about the color,
   just apply the pixel value. The routines that draw lines
   (PolyLine, PolySegment, PolyRect, and PolyArc) use the line
   width, line style, cap style, and join style. Line width is in
   pixels. The line style specifies whether it is solid or dashed,
   and what kind of dash. The cap style specifies whether Rounded,
   Butt, etc. The join style specifies whether joins between
   joined lines are Miter, Round or Beveled. When lines cross as
   part of the same polyline, they are assumed to be drawn once.
   (See the X protocol specification for more details.) Zero-width
   lines are NOT meant to be really zero width; this is the
   client's way of telling you that you can optimize line drawing
   with little regard to the end caps and joins. They are called
   "thin" lines and are meant to be one pixel wide. These are
   frequently done in hardware or in a streamlined assembly
   language routine. Lines with widths greater than zero, though,
   must all be drawn with the same algorithm, because client
   software assumes that every jag on every line at an angle will
   come at the same place. Two lines that should have one pixel in
   the space between them (because of their distance apart and
   their widths) should have such a one-pixel line of space
   between them if drawn, regardless of angle. The solid area fill
   routines (FillPolygon, PolyFillRect, PolyFillArc) all use the
   fill rule, which specifies subtle interpretations of what
   points are inside and what are outside of a given polygon. The
   PolyFillArc routine also uses the arc mode, which specifies
   whether to fill pie segments or single-edge slices of an
   ellipse. The line drawing, area fill, and PolyText routines
   must all apply the correct "fill style." This can be either a
   solid foreground color, a transparent stipple, an opaque
   stipple, or a tile. Stipples are bitmaps where the 1 bits
   represent that the foreground color is written, and 0 bits
   represent that either the pixel is left alone (transparent) or
   that the background color is written (opaque). A tile is a
   pixmap of the full depth of the GC that is applied in its full
   glory to all areas. The stipple and tile patterns can be any
   rectangular size, although some implementations will be faster
   for certain sizes such as 8x8 or 32x32. The mi implementation
   passes this responsibility down to the Pixblit routines. See
   the X protocol document for full details. The description of
   the CreateGC request has a very good, detailed description of
   these attributes.The Primitives The Drawing Primitives are as
   follows: RegionPtr pGC->ops->CopyArea(src, dst, pGC, srcx,
   srcy, w, h, dstx, dsty) DrawablePtr dst, src; GCPtr pGC; int
   srcx, srcy, w, h, dstx, dsty; CopyArea copies a rectangle of
   pixels from one drawable to another of the same depth. To
   effect scrolling, this must be able to copy from any drawable
   to itself, overlapped. No squeezing or stretching is done
   because the source and destination are the same size. However,
   everything is still clipped to the clip regions of the
   destination drawable. If pGC->graphicsExposures is True, any
   portions of the destination which were not valid in the source
   (either occluded by covering windows, or outside the bounds of
   the drawable) should be collected together and returned as a
   region (if this resultant region is empty, NULL can be returned
   instead). Furthermore, the invalid bits of the source are not
   copied to the destination and (when the destination is a
   window) are filled with the background tile. The sample routine
   miHandleExposures generates the appropriate return value and
   fills the invalid area using pScreen->PaintWindowBackground.
   For instance, imagine a window that is partially obscured by
   other windows in front of it. As text is scrolled on your
   window, the pixels that are scrolled out from under obscuring
   windows will not be available on the screen to copy to the
   right places, and so an exposure event must be sent for the
   client to correctly repaint them. Of course, if you implement
   some sort of backing store, you could do this without resorting
   to exposure events. An example implementation is mfbCopyArea()
   in Xserver/mfb/mfbbitblt.c. RegionPtr pGC->ops->CopyPlane(src,
   dst, pGC, srcx, srcy, w, h, dstx, dsty, plane) DrawablePtr dst,
   src; GCPtr pGC; int srcx, srcy, w, h, dstx, dsty; unsigned long
   plane; CopyPlane must copy one plane of a rectangle from the
   source drawable onto the destination drawable. Because this
   routine only copies one bit out of each pixel, it can copy
   between drawables of different depths. This is the only way of
   copying between drawables of different depths, except for
   copying bitmaps to pixmaps and applying foreground and
   background colors to it. All other conditions of CopyArea apply
   to CopyPlane too. An example implementation is mfbCopyPlane()
   in Xserver/mfb/mfbbitblt.c. void pGC->ops->PolyPoint(dst, pGC,
   mode, n, pPoint) DrawablePtr dst; GCPtr pGC; int mode; int n;
   DDXPointPtr pPoint; PolyPoint draws a set of one-pixel dots
   (foreground color) at the locations given in the array. mode is
   one of the defined constants Origin (absolute coordinates) or
   Previous (each coordinate is relative to the last). Note that
   this does not use the background color or any tiles or
   stipples. Example implementations are mfbPolyPoint() in
   Xserver/mfb/mfbpolypnt.c and miPolyPoint in
   Xserver/mi/mipolypnt.c. void pGC->ops->Polylines(dst, pGC,
   mode, n, pPoint) DrawablePtr dst; GCPtr pGC; int mode; int n;
   DDXPointPtr pPoint; Similar to PolyPoint, Polylines draws lines
   between the locations given in the array. Zero-width lines are
   NOT meant to be really zero width; this is the client's way of
   telling you that you can maximally optimize line drawing with
   little regard to the end caps and joins. mode is one of the
   defined constants Previous or Origin, depending upon whether
   the points are each relative to the last or are absolute.
   Example implementations are miWideLine() and miWideDash() in
   mi/miwideline.c and miZeroLine() in mi/mizerline.c. void
   pGC->ops->PolySegment(dst, pGC, n, pPoint) DrawablePtr dst;
   GCPtr pGC; int n; xSegment *pSegments; PolySegments draws
   unconnected lines between pairs of points in the array; the
   array must be of even size; no interconnecting lines are drawn.
   An example implementation is miPolySegment() in mipolyseg.c.
   void pGC->ops->PolyRectangle(dst, pGC, n, pRect) DrawablePtr
   dst; GCPtr pGC; int n; xRectangle *pRect; PolyRectangle draws
   outlines of rectangles for each rectangle in the array. An
   example implementation is miPolyRectangle() in
   Xserver/mi/mipolyrect.c. void pGC->ops->PolyArc(dst, pGC, n,
   pArc) DrawablePtr dst; GCPtr pGC; int n; xArc*pArc; PolyArc
   draws connected conic arcs according to the descriptions in the
   array. See the protocol specification for more details. Example
   implementations are miZeroPolyArc in Xserver/mi/mizerarc. and
   miPolyArc() in Xserver/mi/miarc.c. void
   pGC->ops->FillPolygon(dst, pGC, shape, mode, count, pPoint)
   DrawablePtr dst; GCPtr pGC; int shape; int mode; int count;
   DDXPointPtr pPoint; FillPolygon fills a polygon specified by
   the points in the array with the appropriate fill style. If
   necessary, an extra border line is assumed between the starting
   and ending lines. The shape can be used as a hint to optimize
   filling; it indicates whether it is convex (all interior angles
   less than 180), nonconvex (some interior angles greater than
   180 but border does not cross itself), or complex (border
   crosses itself). You can choose appropriate algorithms or
   hardware based upon mode. mode is one of the defined constants
   Previous or Origin, depending upon whether the points are each
   relative to the last or are absolute. An example implementation
   is miFillPolygon() in Xserver/mi/mipoly.c. void
   pGC->ops->PolyFillRect(dst, pGC, n, pRect) DrawablePtr dst;
   GCPtr pGC; int n; xRectangle *pRect; PolyFillRect fills
   multiple rectangles. Example implementations are
   mfbPolyFillRect() in Xserver/mfb/mfbfillrct.c and
   miPolyFillRect() in Xserver/mi/mifillrct.c. void
   pGC->ops->PolyFillArc(dst, pGC, n, pArc) DrawablePtr dst; GCPtr
   pGC; int n; xArc *pArc; PolyFillArc fills a shape for each arc
   in the list that is bounded by the arc and one or two line
   segments with the current fill style. An example implementation
   is miPolyFillArc() in Xserver/mi/mifillarc.c. void
   pGC->ops->PutImage(dst, pGC, depth, x, y, w, h, leftPad,
   format, pBinImage) DrawablePtr dst; GCPtr pGC; int x, y, w, h;
   int format; char *pBinImage; PutImage copies a pixmap image
   into the drawable. The pixmap image must be in X protocol
   format (either Bitmap, XYPixmap, or ZPixmap), and format tells
   the format. (See the X protocol specification for details on
   these formats). You must be able to accept all three formats,
   because the client gets to decide which format to send. Either
   the drawable and the pixmap image have the same depth, or the
   source pixmap image must be a Bitmap. If a Bitmap, the
   foreground and background colors will be applied to the
   destination. An example implementation is miPutImage() in
   Xserver/mfb/mibitblt.c. void pScreen->GetImage(src, x, y, w, h,
   format, planeMask, pBinImage) DrawablePtr src; int x, y, w, h;
   unsigned int format; unsigned long planeMask; char *pBinImage;
   GetImage copies the bits from the source drawable into the
   destination pointer. The bits are written into the buffer
   according to the server-defined pixmap padding rules. pBinImage
   is guaranteed to be big enough to hold all the bits that must
   be written. This routine does not correspond exactly to the X
   protocol GetImage request, since DIX has to break the reply up
   into buffers of a size requested by the transport layer. If
   format is ZPixmap, the bits are written in the ZFormat for the
   depth of the drawable; if there is a 0 bit in the planeMask for
   a particular plane, all pixels must have the bit in that plane
   equal to 0. If format is XYPixmap, planemask is guaranteed to
   have a single bit set; the bits should be written in Bitmap
   format, which is the format for a single plane of an XYPixmap.
   An example implementation is miGetImage() in
   Xserver/mi/mibitblt.c. void pGC->ops->ImageText8(pDraw, pGC, x,
   y, count, chars) DrawablePtr pDraw; GCPtr pGC; int x, y; int
   count; char *chars; ImageText8 draws text. The text is drawn in
   the foreground color; the background color fills the remainder
   of the character rectangles. The coordinates specify the
   baseline and start of the text. An example implementation is
   miImageText8() in Xserver/mi/mipolytext.c. int
   pGC->ops->PolyText8(pDraw, pGC, x, y, count, chars) DrawablePtr
   pDraw; GCPtr pGC; int x, y; int count; char *chars; PolyText8
   works like ImageText8, except it draws with the current fill
   style for special effects such as shaded text. See the X
   protocol specification for more details. An example
   implementation is miPolyText8() in Xserver/mi/mipolytext.c. int
   pGC->ops->PolyText16(pDraw, pGC, x, y, count, chars)
   DrawablePtr pDraw; GCPtr pGC; int x, y; int count; unsigned
   short *chars; void pGC->ops->ImageText16(pDraw, pGC, x, y,
   count, chars) DrawablePtr pDraw; GCPtr pGC; int x, y; int
   count; unsigned short *chars; These two routines are the same
   as the "8" versions, except that they are for 16-bit character
   codes (useful for oriental writing systems). The primary
   difference is in the way the character information is looked
   up. The 8-bit and the 16-bit versions obviously have different
   kinds of character values to look up; the main goal of the
   lookup is to provide a pointer to the CharInfo structs for the
   characters to draw and to pass these pointers to the Glyph
   routines. Given a CharInfo struct, lower-level software can
   draw the glyph desired with little concern for other
   characteristics of the font. 16-bit character fonts have a
   row-and-column scheme, where the 2bytes of the character code
   constitute the row and column in a square matrix of CharInfo
   structs. Each font has row and column minimum and maximum
   values; the CharInfo structures form a two-dimensional matrix.
   Example implementations are miPolyText16() and miImageText16()
   in Xserver/mi/mipolytext.c. See the X protocol specification
   for more details on these graphic operations. There is a hook
   in the GC ops, called LineHelper, that used to be used in the
   sample implementation by the code for wide lines. It no longer
   servers any purpose in the sample servers, but still exists,
   #ifdef'ed by NEED_LINEHELPER, in case someone needs it.Pixblit
   Procedures The Drawing Primitive functions must be defined for
   your server. One possible way to do this is to use the mi
   routines from the sample server. If you choose to use the mi
   routines (even part of them!) you must implement these Pixblit
   routines. These routines read and write pixel values and deal
   directly with the image data. The Pixblit routines for the
   sample server are part of the "mfb" routines (for Monochrome
   Frame Buffer), and "cfb" routines (for Color Frame Buffer). As
   with the mi routines, the mfb and cfb routines are portable but
   are not as portable as the mi routines. The mfb routines only
   work for monochrome frame buffers, the simplest type of
   display. Furthermore, they only work for screens that organize
   their bits in rows of pixels on the screen. (See the Strategies
   document for more details on porting mfb.) The cfb routines
   work for packed-pixel displays from 2 to 32 bits in depth,
   although they have a bit of code which has been tuned to run on
   8-bit (1 pixel per byte) displays. In other words, if you have
   a "normal" frame buffer type display, you can probably use
   either the mfb or cfb code, and the mi code. If you have a
   stranger hardware, you will have to supply your own Pixblit
   routines, but you can use the mi routines on top of them. If
   you have better ways of doing some of the Drawing Primitive
   functions, then you may want to supply some of your own Drawing
   Primitive routines. (Even people who write their own Drawing
   Primitives save at least some of the mi code for certain
   special cases that their hardware or library or fancy algorithm
   does not handle.) The client, DIX, and the machine-independent
   routines do not carry the final responsibility of clipping.
   They all depend upon the Pixblit routines to do their clipping
   for them. The rule is, if you touch the frame buffer, you clip.
   (The higher level routines may decide to clip at a high level,
   but this is only for increased performance and cannot
   substitute for bottom-level clipping. For instance, the mi
   routines, DIX, or the client may decide to check all character
   strings to be drawn and chop off all characters that would not
   be displayed. If so, it must retain the character on the edge
   that is partly displayed so that the Pixblit routines can clip
   off precisely at the right place.) To make this easier, all of
   the reasons to clip can be combined into one region in your
   ValidateGC procedure. You take this composite clip region with
   you into the Pixblit routines. (The sample server does this.)
   Also, FillSpans() has to apply tile and stipple patterns. The
   patterns are all aligned to the window origin so that when two
   people write patches that are contiguous, they will merge
   nicely. (Really, they are aligned to the patOrg point in the
   GC. This defaults to (0, 0) but can be set by the client to
   anything.) However, the mi routines can translate (relocate)
   the points from window-relative to screen-relative if desired.
   If you set the miTranslate field in the GC (set it in the
   CreateGC or ValidateGC routine), then the mi output routines
   will translate all coordinates. If it is false, then the
   coordinates will be passed window-relative. Screens with no
   hardware translation will probably set miTranslate to TRUE, so
   that geometry (e.g. polygons, rectangles) can be translated,
   rather than having the resulting list of scanlines translated;
   this is good because the list vertices in a drawing request
   will generally be much smaller than the list of scanlines it
   produces. Similarly, hardware that does translation can set
   miTranslate to FALSE, and avoid the extra addition per vertex,
   which can be (but is not always) important for getting the
   highest possible performance. (Contrast the behavior of
   GetSpans, which is not expected to be called as often, and so
   has different constraints.) The miTranslate field is settable
   in each GC, if , for example, you are mixing several kinds of
   destinations (offscreen pixmaps, main memory pixmaps, backing
   store, and windows), all of which have different requirements,
   on one screen. As with other drawing routines, there are fields
   in the GC to direct higher code to the correct routine to
   execute for each function. In this way, you can optimize for
   special cases, for example, drawing solids versus drawing
   stipples. The Pixblit routines are broken up into three sets.
   The Span routines simply fill in rows of pixels. The Glyph
   routines fill in character glyphs. The PushPixels routine is a
   three-input bitblt for more sophisticated image creation. It
   turns out that the Glyph and PushPixels routines actually have
   a machine-independent implementation that depends upon the Span
   routines. If you are really pressed for time, you can use these
   versions, although they are quite slow.Span Routines For these
   routines, all graphic operations have been reduced to "spans."
   A span is a horizontal row of pixels. If you can design these
   routines which write into and read from rows of pixels at a
   time, you can use the mi routines. Each routine takes a
   destination drawable to draw into, a GC to use while drawing,
   the number of spans to do, and two pointers to arrays that
   indicate the list of starting points and the list of widths of
   spans. void pGC->ops->FillSpans(dst, pGC, nSpans, pPoints,
   pWidths, sorted) DrawablePtr dst; GCPtr pGC; int nSpans;
   DDXPointPtr pPoints; int *pWidths; int sorted; FillSpans should
   fill horizontal rows of pixels with the appropriate patterns,
   stipples, etc., based on the values in the GC. The starting
   points are in the array at pPoints; the widths are in pWidths.
   If sorted is true, the scan lines are in increasing y order, in
   which case you may be able to make assumptions and
   optimizations. GC components: alu, clipOrg, clientClip, and
   fillStyle. GC mode-dependent components: fgPixel (for fillStyle
   Solid); tile, patOrg (for fillStyle Tile); stipple, patOrg,
   fgPixel (for fillStyle Stipple); and stipple, patOrg, fgPixel
   and bgPixel (for fillStyle OpaqueStipple). void
   pGC->ops->SetSpans(pDrawable, pGC, pSrc, ppt, pWidths, nSpans,
   sorted) DrawablePtr pDrawable; GCPtr pGC; char *pSrc;
   DDXPointPtr pPoints; int *pWidths; int nSpans; int sorted; For
   each span, this routine should copy pWidths bits from pSrc to
   pDrawable at pPoints using the raster-op from the GC. If sorted
   is true, the scan lines are in increasing y order. The pixels
   in pSrc are padded according to the screen's padding rules.
   These can be used to support interesting extension libraries,
   for example, shaded primitives. It does not use the tile and
   stipple. GC components: alu, clipOrg, and clientClip The above
   functions are expected to handle all modifiers in the current
   GC. Therefore, it is expedient to have different routines to
   quickly handle common special cases and reload the procedure
   pointers at validate time, as with the other output functions.
   void pScreen->GetSpans(pDrawable, wMax, pPoints, pWidths,
   nSpans) DrawablePtr pDrawable; int wMax; DDXPointPtr pPoints;
   int *pWidths; int nSpans; char *pDst; For each span, GetSpans
   gets bits from the drawable starting at pPoints and continuing
   for pWidths bits. Each scanline returned will be
   server-scanline padded. The routine can return NULL if memory
   cannot be allocated to hold the result. GetSpans never
   translates -- for a window, the coordinates are already
   screen-relative. Consider the case of hardware that doesn't do
   translation: the mi code that calls ddX will translate each
   shape (rectangle, polygon,. etc.) before scan-converting it,
   which requires many fewer additions that having GetSpans
   translate each span does. Conversely, consider hardware that
   does translate: it can set its translation point to (0, 0) and
   get each span, and the only penalty is the small number of
   additions required to translate each shape being scan-converted
   by the calling code. Contrast the behavior of FillSpans and
   SetSpans (discussed above under miTranslate), which are
   expected to be used more often. Thus, the penalty to hardware
   that does hardware translation is negligible, and code that
   wants to call GetSpans() is greatly simplified, both for
   extensions and the machine-independent core
   implementation.Glyph Routines The Glyph routines draw
   individual character glyphs for text drawing requests. You have
   a choice in implementing these routines. You can use the mi
   versions; they depend ultimately upon the span routines.
   Although text drawing will work, it will be very slow. void
   pGC->ops->PolyGlyphBlt(pDrawable, pGC, x, y, nglyph, ppci,
   pglyphBase) DrawablePtr pDrawable; GCPtr pGC; int x , y;
   unsigned int nglyph; CharInfoRec **ppci; /* array of character
   info */ pointer unused; /* unused since R5 */ GC components:
   alu, clipOrg, clientClip, font, and fillStyle. GC
   mode-dependent components: fgPixel (for fillStyle Solid); tile,
   patOrg (for fillStyle Tile); stipple, patOrg, fgPixel (for
   fillStyle Stipple); and stipple, patOrg, fgPixel and bgPixel
   (for fillStyle OpaqueStipple). void
   pGC->ops->ImageGlyphBlt(pDrawable, pGC, x, y, nglyph, ppci,
   pglyphBase) DrawablePtr pDrawable; GCPtr pGC; int x , y;
   unsigned int nglyph; CharInfoRec **ppci; /* array of character
   info */ pointer unused; /* unused since R5 */ GC components:
   clipOrg, clientClip, font, fgPixel, bgPixel These routines must
   copy the glyphs defined by the bitmaps in pglyphBase and the
   font metrics in ppci to the DrawablePtr, pDrawable. The poly
   routine follows all fill, stipple, and tile rules. The image
   routine simply blasts the glyph onto the glyph's rectangle, in
   foreground and background colors. More precisely, the Image
   routine fills the character rectangle with the background
   color, and then the glyph is applied in the foreground color.
   The glyph can extend outside of the character rectangle.
   ImageGlyph() is used for terminal emulators and informal text
   purposes such as button labels. The exact specification for the
   Poly routine is that the glyph is painted with the current fill
   style. The character rectangle is irrelevant for this
   operation. PolyText, at a higher level, includes facilities for
   font changes within strings and such; it is to be used for
   WYSIWYG word processing and similar systems. Both of these
   routines must clip themselves to the overall clipping region.
   Example implementations in mi are miPolyGlyphBlt() and
   miImageGlyphBlt() in Xserver/mi/miglblt.c.PushPixels routine
   The PushPixels routine writes the current fill style onto the
   drawable in a certain shape defined by a bitmap. PushPixels is
   equivalent to using a second stipple. You can thing of it as
   pushing the fillStyle through a stencil. PushPixels is not used
   by any of the mi rendering code, but is used by the mi software
   cursor code. Suppose the stencil is: 00111100 and the stipple
   is: 10101010 PushPixels result: 00101000 You have a choice in
   implementing this routine. You can use the mi version which
   depends ultimately upon FillSpans(). Although it will work, it
   will be slow. void pGC->ops->PushPixels(pGC, pBitMap,
   pDrawable, dx, dy, xOrg, yOrg) GCPtr pGC; PixmapPtr pBitMap;
   DrawablePtr pDrawable; int dx, dy, xOrg, yOrg; GC components:
   alu, clipOrg, clientClip, and fillStyle. GC mode-dependent
   components: fgPixel (for fillStyle Solid); tile, patOrg (for
   fillStyle Tile); stipple, patOrg, fgPixel (for fillStyle
   Stipple); and stipple, patOrg, fgPixel and bgPixel (for
   fillStyle OpaqueStipple). PushPixels applys the foreground
   color, tile, or stipple from the pGC through a stencil onto
   pDrawable. pBitMap points to a stencil (of which we use an area
   dx wide by dy high), which is oriented over the drawable at
   xOrg, yOrg. Where there is a 1 bit in the bitmap, the
   destination is set according to the current fill style. Where
   there is a 0 bit in the bitmap, the destination is left the way
   it is. This routine must clip to the overall clipping region.
   An Example implementation is miPushPixels() in
   Xserver/mi/mipushpxl.c.Shutdown Procedures void AbortDDX() void
   ddxGiveUp() Some hardware may require special work to be done
   before the server exits so that it is not left in an
   intermediate state. As explained in the OS layer, FatalError()
   will call AbortDDX() just before terminating the server. In
   addition, ddxGiveUp() will be called just before terminating
   the server on a "clean" death. What AbortDDX() and ddxGiveUP do
   is left unspecified, only that stubs must exist in the ddx
   layer. It is up to local implementors as to what they should
   accomplish before termination.Command Line Procedures int
   ddxProcessArgument(argc, argv, i) int argc; char *argv[]; int
   i; void ddxUseMsg() You should write these routines to deal
   with device-dependent command line arguments. The routine
   ddxProcessArgument() is called with the command line, and the
   current index into argv; you should return zero if the argument
   is not a device-dependent one, and otherwise return a count of
   the number of elements of argv that are part of this one
   argument. For a typical option (e.g., "-realtime"), you should
   return the value one. This routine gets called before checks
   are made against device-independent arguments, so it is
   possible to peek at all arguments or to override
   device-independent argument processing. You can document the
   device-dependent arguments in ddxUseMsg(), which will be called
   from UseMsg() after printing out the device-independent
   arguments.Wrappers and devPrivates Two new extensibility
   concepts have been developed for release 4, Wrappers and
   devPrivates. These replace the R3 GCInterest queues, which were
   not a general enough mechanism for many extensions and only
   provided hooks into a single data structure.devPrivates
   devPrivates are arrays of values attached to various data
   structures (Screens, GCs, Windows, and Pixmaps currently).
   These arrays are sized dynamically at server startup (and
   reset) time as various modules allocate portions of them. They
   can be used for any purpose; each array entry is actually a
   union, DevUnion, of common useful types (pointer, long and
   unsigned long). devPrivates must be allocated on startup and
   whenever the server resets. To make this easier, the global
   variable "serverGeneration" is incremented each time
   devPrivates should be allocated, but before the initialization
   process begins, typical usage would be: static int
   privateGeneration = 0; if (privateGeneration !=
   serverGeneration) { allocate devPrivates here.
   privateGeneration = serverGeneration; } Screen devPrivates An
   index into every screen devPrivates array is allocated with int
   AllocateScreenPrivateIndex() This call can occur at any time,
   each existing devPrivates array is resized to accommodate the
   new entry. This routine returns -1 indicating an allocation
   failure. Otherwise, the return value can be used to index the
   array of devPrivates on any screen: private = (PrivatePointer)
   pScreen->devPrivates[screenPrivateIndex].ptr; The pointer in
   each screen is not initialized by
   AllocateScreenPrivateIndex().Window devPrivates An index into
   every window devPrivates array is allocated with int
   AllocateWindowPrivateIndex () AllocateWindowPrivateIndex()
   never returns an error. This call must be associated with a
   call which causes a chunk of memory to be automatically
   allocated and attached to the devPrivate entry on every screen
   which the module will need to use the index: Bool
   AllocateWindowPrivate (pScreen, index, amount) ScreenPtr
   pScreen; int index; unsigned amount; If this space is not
   always needed for every object, use 0 as the amount. In this
   case, the pointer field of the entry in the devPrivates array
   is initialized to NULL. This call exists so that DIX may
   preallocate all of the space required for an object with one
   call; this reduces memory fragmentation considerably.
   AllocateWindowPrivate returns FALSE on allocation failure. Both
   of these calls must occur before any window structures are
   allocated; the server is careful to avoid window creation until
   all modules are initialized, but do not call this after
   initialization. A typical allocation sequence for
   WindowPrivates would be: privateInitialize (pScreen) ScreenPtr
   pScreen; { if (privateGeneration != serverGeneration) {
   windowPrivateIndex = AllocateWindowPrivateIndex();
   privateGeneration = serverGeneration; } return
   (AllocateWindowPrivate(pScreen, windowPrivateIndex,
   sizeof(windowPrivateStructure))); } GC and Pixmap devPrivates
   The calls for GCs and Pixmaps mirror the Window calls exactly;
   they have the same requirements and limitations: int
   AllocateGCPrivateIndex () Bool AllocateGCPrivate (pScreen,
   index, amount) ScreenPtr pScreen; int index; unsigned amount;
   int AllocatePixmapPrivateIndex () Bool AllocatePixmapPrivate
   (pScreen, index, amount) ScreenPtr pScreen; int index; unsigned
   amount; Wrappers Wrappers are not a body of code, nor an
   interface spec. They are, instead, a technique for hooking a
   new module into an existing calling sequence. There are
   limitations on other portions of the server implementation
   which make using wrappers possible; limits on when specific
   fields of data structures may be modified. They are intended as
   a replacement for GCInterest queues, which were not general
   enough to support existing modules; in particular software
   cursors and backing store both needed more control over the
   activity. The general mechanism for using wrappers is:
   privateWrapperFunction (object, ...) ObjectPtr object; {
   pre-wrapped-function-stuff ... object->functionVector = (void
   *) object->devPrivates[privateIndex].ptr;
   (*object->functionVector) (object, ...); /* * this next line is
   occasionally required by the rules governing * wrapper
   functions. Always using it will not cause problems. * Not using
   it when necessary can cause severe troubles. */
   object->devPrivates[privateIndex].ptr = (pointer)
   object->functionVector; object->functionVector =
   privateWrapperFunction; post-wrapped-function-stuff ... }
   privateInitialize (object) ObjectPtr object; {
   object->devPrivates[privateIndex].ptr = (pointer)
   object->functionVector; object->functionVector =
   privateWrapperFunction; } Thus the privateWrapperFunction
   provides hooks for performing work both before and after the
   wrapped function has been called; the process of resetting the
   functionVector is called "unwrapping" while the process of
   fetching the wrapped function and replacing it with the
   wrapping function is called "wrapping". It should be clear that
   GCInterest queues could be emulated using wrappers. In general,
   any function vectors contained in objects can be wrapped, but
   only vectors in GCs and Screens have been tested. Wrapping
   screen functions is quite easy; each vector is individually
   wrapped. Screen functions are not supposed to change after
   initialization, so rewrapping is technically not necessary, but
   causes no problems. Wrapping GC functions is a bit more
   complicated. GC's have two tables of function vectors, one
   hanging from gc->ops and the other from gc->funcs, which should
   be initially wrapped from a CreateGC wrapper. Wrappers should
   modify only table pointers, not the contents of the tables, as
   they may be shared by more than one GC (and, in the case of
   funcs, are probably shared by all gcs). Your func wrappers may
   change the GC funcs or ops pointers, and op wrappers may change
   the GC op pointers but not the funcs. Thus, the rule for GC
   wrappings is: wrap the funcs from CreateGC and, in each func
   wrapper, unwrap the ops and funcs, call down, and re-wrap. In
   each op wrapper, unwrap the ops, call down, and rewrap
   afterwards. Note that in re-wrapping you must save out the
   pointer you're replacing again. This way the chain will be
   maintained when wrappers adjust the funcs/ops tables they
   use.Work Queue To queue work for execution when all clients are
   in a stable state (i.e. just before calling select() in
   WaitForSomething), call: Bool
   QueueWorkProc(function,client,closure) Bool (*function)();
   ClientPtr client; pointer closure; When the server is about to
   suspend itself, the given function will be executed:
   (*function) (client, closure) Neither client nor closure are
   actually used inside the work queue routines.Summary of
   Routines This is a summary of the routines discussed in this
   document. The procedure names are in alphabetical order. The
   Struct is the structure it is attached to; if blank, this
   procedure is not attached to a struct and must be named as
   shown. The sample server provides implementations in the
   following categories. Notice that many of the graphics routines
   have both mi and mfb implementations. dix portable to all
   systems; do not attempt to rewrite (Xserver/dix)os routine
   provided in Xserver/os or Xserver/include/os.hddx frame buffer
   dependent (examples in Xserver/mfb,Xserver/cfb)mi routine
   provided in Xserver/mihd hardware dependent (examples in many
   Xserver/hw directories)none not implemented in sample
   implementation Server Routines (Page
   1)ProcedurePortStructALLOCATE_LOCALosAbortDDXhdAddCallbackdixAd
   dEnabledDeviceosAddInputDevicedixAddScreendixAdjustWaitForDelay
   osBellhdDeviceChangeClipmiGC funcChangeGCGC
   funcChangeWindowAttributesddxScreenClearToBackgroundddxWindowCl
   ientAuthorizedosClientSignaldixClientSleepdixClientWakeupdixCli
   pNotifyddxScreenCloseScreenhdConstrainCursorhdScreenCopyAreamiG
   C opCopyGCDestddxGC funcCopyGCSourcenoneGC funcCopyPlanemiGC
   opCopyWindowddxWindowCreateGCddxScreenCreateCallbackListdixCrea
   tePixmapddxScreenCreateScreenResourcesddxScreenCreateWellKnowSo
   cketsosCreateWindowddxScreenCursorLimitshdScreenDEALLOCATE_LOCA
   LosDeleteCallbackdixDeleteCallbackListdixDestroyClipddxGC
   funcDestroyGCddxGC
   funcDestroyPixmapddxScreenDestroyWindowddxScreenDisplayCursorhd
   ScreenErrorosErrorFosFatalErrorosFillPolygonmiGC
   opFillSpansddxGC
   opFlushAllOutputosFlushIfCriticalOutputPendingosFreeScratchPixm
   apHeaderdixGetImagemiScreenGetMotionEventshdDeviceGetScratchPix
   mapHeaderdixGetSpansddxScreenGetStaticColormapddxScreenServer
   Routines (Page 2)ProcedurePortStructImageGlyphBltmiGC
   opImageText16miGC opImageText8miGC
   opInitInputhdInitKeyboardDeviceStructdixInitOutputhdInitPointer
   DeviceStructdixInsertFakeRequestosInstallColormapddxScreenInter
   sectmiScreenInversemiScreenLegalModifierhdLineHelpermiGC
   opListInstalledColormapsddxScreenLookupKeyboardDevicedixLookupP
   ointerDevicedixModifyPixmapheadermiScreenNextAvailableClientdix
   OsInitosPaintWindowBackgroundmiWindowPaintWindowBordermiWindowP
   ointerNonInterestBoxhdScreenPointInRegionmiScreenPolyArcmiGC
   opPolyFillArcmiGC opPolyFillRectmiGC opPolyGlyphBltmiGC
   opPolylinesmiGC opPolyPointmiGC opPolyRectanglemiGC
   opPolySegmentmiGC opPolyText16miGC opPolyText8miGC
   opPositionWindowddxScreenProcessInputEventshdPushPixelsmiGC
   opPutImagemiGC
   opQueryBestSizehdScreenReadRequestFromClientosRealizeCursorhdSc
   reenRealizeFontddxScreenRealizeWindowddxScreenRecolorCursorhdSc
   reenRectInmiScreenRegionCopymiScreenRegionCreatemiScreenRegionD
   estroymiScreenRegionEmptymiScreenRegionExtentsmiScreenRegionNot
   EmptymiScreenRegionResetmiScreenResolveColorddxScreenServer
   Routines (Page
   3)ProcedurePortStructRegisterKeyboardDevicedixRegisterPointerDe
   vicedixRemoveEnabledDeviceosResetCurrentRequestosRestoreAreasno
   neBackingStoreSaveDoomedAreasnoneBackingStoreSaveScreenddxScree
   nSetCriticalOutputPendingosSetCursorPositionhdScreenSetInputChe
   ckdixSetSpansddxGC
   opStoreColorsddxScreenSubtractmiScreenTimerCancelosTimerCheckos
   TimerForceosTimerFreeosTimerInitosTimerSetosTimeSinceLastInputE
   venthdTranslateBackingStorenoneBackingStoreTranslateRegionmiScr
   eenUninstallColormapddxScreenUnionmiScreenUnrealizeCursorhdScre
   enUnrealizeFontddxScreenUnrealizeWindowddxScreenValidateGCddxGC
   funcValidateTreemiScreenWaitForSomethingosWindowExposuresmiWind
   owWriteToClientosXallocosXfreeosXreallocos
