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+<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+ "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+]>
+
+<article>
+
+ <articleinfo>
+ <!-- Title information -->
+ <title>Distributed Multihead X design</title>
+ <authorgroup>
+ <author><firstname>Kevin E.</firstname><surname>Martin</surname></author>
+ <author><firstname>David H.</firstname><surname>Dawes</surname></author>
+ <author><firstname>Rickard E.</firstname><surname>Faith</surname></author>
+ </authorgroup>
+ <pubdate>29 June 2004 (created 25 July 2001)</pubdate>
+ <abstract><para>
+ This document covers the motivation, background, design, and
+ implementation of the distributed multihead X (DMX) system. It
+ is a living document and describes the current design and
+ implementation details of the DMX system. As the project
+ progresses, this document will be continually updated to reflect
+ the changes in the code and/or design. <emphasis remap="it">Copyright 2001 by VA
+ Linux Systems, Inc., Fremont, California. Copyright 2001-2004
+ by Red Hat, Inc., Raleigh, North Carolina</emphasis>
+ </para></abstract>
+ </articleinfo>
+
+<!-- Begin the document -->
+<sect1>
+<title>Introduction</title>
+
+<sect2>
+<title>The Distributed Multihead X Server</title>
+
+<para>Current Open Source multihead solutions are limited to a single
+physical machine. A single X server controls multiple display devices,
+which can be arranged as independent heads or unified into a single
+desktop (with Xinerama). These solutions are limited to the number of
+physical devices that can co-exist in a single machine (e.g., due to the
+number of AGP/PCI slots available for graphics cards). Thus, large
+tiled displays are not currently possible. The work described in this
+paper will eliminate the requirement that the display devices reside in
+the same physical machine. This will be accomplished by developing a
+front-end proxy X server that will control multiple back-end X servers
+that make up the large display.
+</para>
+
+<para>The overall structure of the distributed multihead X (DMX) project is
+as follows: A single front-end X server will act as a proxy to a set of
+back-end X servers, which handle all of the visible rendering. X
+clients will connect to the front-end server just as they normally would
+to a regular X server. The front-end server will present an abstracted
+view to the client of a single large display. This will ensure that all
+standard X clients will continue to operate without modification
+(limited, as always, by the visuals and extensions provided by the X
+server). Clients that are DMX-aware will be able to use an extension to
+obtain information about the back-end servers (e.g., for placement of
+pop-up windows, window alignments by the window manager, etc.).
+</para>
+
+<para>The architecture of the DMX server is divided into two main sections:
+input (e.g., mouse and keyboard events) and output (e.g., rendering and
+windowing requests). Each of these are describe briefly below, and the
+rest of this design document will describe them in greater detail.
+</para>
+
+<para>The DMX server can receive input from three general types of input
+devices: "local" devices that are physically attached to the machine on
+which DMX is running, "backend" devices that are physically attached to
+one or more of the back-end X servers (and that generate events via the
+X protocol stream from the backend), and "console" devices that can be
+abstracted from any non-back-end X server. Backend and console devices
+are treated differently because the pointer device on the back-end X
+server also controls the location of the hardware X cursor. Full
+support for XInput extension devices is provided.
+</para>
+
+<para>Rendering requests will be accepted by the front-end server; however,
+rendering to visible windows will be broken down as needed and sent to
+the appropriate back-end server(s) via X11 library calls for actual
+rendering. The basic framework will follow a Xnest-style approach. GC
+state will be managed in the front-end server and sent to the
+appropriate back-end server(s) as required. Pixmap rendering will (at
+least initially) be handled by the front-end X server. Windowing
+requests (e.g., ordering, mapping, moving, etc.) will handled in the
+front-end server. If the request requires a visible change, the
+windowing operation will be translated into requests for the appropriate
+back-end server(s). Window state will be mirrored in the back-end
+server(s) as needed.
+</para>
+</sect2>
+
+<sect2>
+<title>Layout of Paper</title>
+
+<para>The next section describes the general development plan that was
+actually used for implementation. The final section discusses
+outstanding issues at the conclusion of development. The first appendix
+provides low-level technical detail that may be of interest to those
+intimately familiar with the X server architecture. The final appendix
+describes the four phases of development that were performed during the
+first two years of development.
+</para>
+
+<para>The final year of work was divided into 9 tasks that are not
+described in specific sections of this document. The major tasks during
+that time were the enhancement of the reconfiguration ability added in
+Phase IV, addition of support for a dynamic number of back-end displays
+(instead of a hard-coded limit), and the support for back-end display
+and input removal and addition. This work is mentioned in this paper,
+but is not covered in detail.
+</para>
+</sect2>
+</sect1>
+
+<!-- ============================================================ -->
+<sect1>
+<title>Development plan</title>
+
+<para>This section describes the development plan from approximately June
+2001 through July 2003.
+</para>
+
+<sect2>
+<title>Bootstrap code</title>
+
+<para>To allow for rapid development of the DMX server by multiple
+developers during the first development stage, the problem will be
+broken down into three tasks: the overall DMX framework, back-end
+rendering services and input device handling services. However, before
+the work begins on these tasks, a simple framework that each developer
+could use was implemented to bootstrap the development effort. This
+framework renders to a single back-end server and provides dummy input
+devices (i.e., the keyboard and mouse). The simple back-end rendering
+service was implemented using the shadow framebuffer support currently
+available in the XFree86 environment.
+</para>
+
+<para>Using this bootstrapping framework, each developer has been able to
+work on each of the tasks listed above independently as follows: the
+framework will be extended to handle arbitrary back-end server
+configurations; the back-end rendering services will be transitioned to
+the more efficient Xnest-style implementation; and, an input device
+framework to handle various input devices via the input extension will
+be developed.
+</para>
+
+<para>Status: The boot strap code is complete. <!-- August 2001 -->
+</para>
+
+</sect2>
+
+<sect2>
+<title>Input device handling</title>
+
+<para>An X server (including the front-end X server) requires two core
+input devices -- a keyboard and a pointer (mouse). These core devices
+are handled and required by the core X11 protocol. Additional types of
+input devices may be attached and utilized via the XInput extension.
+These are usually referred to as ``XInput extension devices'',
+</para>
+
+<para>There are some options as to how the front-end X server gets its core
+input devices:
+
+<orderedlist>
+<listitem>
+ <para>Local Input. The physical input devices (e.g., keyboard and
+ mouse) can be attached directly to the front-end X server. In this
+ case, the keyboard and mouse on the machine running the front-end X
+ server will be used. The front-end will have drivers to read the
+ raw input from those devices and convert it into the required X
+ input events (e.g., key press/release, pointer button press/release,
+ pointer motion). The front-end keyboard driver will keep track of
+ keyboard properties such as key and modifier mappings, autorepeat
+ state, keyboard sound and led state. Similarly the front-end
+ pointer driver will keep track if pointer properties such as the
+ button mapping and movement acceleration parameters. With this
+ option, input is handled fully in the front-end X server, and the
+ back-end X servers are used in a display-only mode. This option was
+ implemented and works for a limited number of Linux-specific
+ devices. Adding additional local input devices for other
+ architectures is expected to be relatively simple.
+</para>
+
+ <para>The following options are available for implementing local input
+ devices:
+
+<orderedlist>
+<listitem>
+ <para>The XFree86 X server has modular input drivers that could
+ be adapted for this purpose. The mouse driver supports a wide
+ range of mouse types and interfaces, as well as a range of
+ Operating System platforms. The keyboard driver in XFree86 is
+ not currently as modular as the mouse driver, but could be made
+ so. The XFree86 X server also has a range of other input
+ drivers for extended input devices such as tablets and touch
+ screens. Unfortunately, the XFree86 drivers are generally
+ complex, often simultaneously providing support for multiple
+ devices across multiple architectures; and rely so heavily on
+ XFree86-specific helper-functions, that this option was not
+ pursued.
+</para>
+</listitem>
+
+<listitem>
+ <para>The <command>kdrive</command> X server in XFree86 has built-in drivers that
+ support PS/2 mice and keyboard under Linux. The mouse driver
+ can indirectly handle other mouse types if the Linux utility
+ <command>gpm</command> is used as to translate the native mouse protocol into
+ PS/2 mouse format. These drivers could be adapted and built in
+ to the front-end X server if this range of hardware and OS
+ support is sufficient. While much simpler than the XFree86
+ drivers, the <command>kdrive</command> drivers were not used for the DMX
+ implementation.
+</para>
+</listitem>
+
+<listitem>
+ <para>Reimplementation of keyboard and mouse drivers from
+ scratch for the DMX framework. Because keyboard and mouse
+ drivers are relatively trivial to implement, this pathway was
+ selected. Other drivers in the X source tree were referenced,
+ and significant contributions from other drivers are noted in
+ the DMX source code.
+</para>
+</listitem>
+</orderedlist>
+</para>
+</listitem>
+
+<listitem>
+ <para>Backend Input. The front-end can make use of the core input
+ devices attached to one or more of the back-end X servers. Core
+ input events from multiple back-ends are merged into a single input
+ event stream. This can work sanely when only a single set of input
+ devices is used at any given time. The keyboard and pointer state
+ will be handled in the front-end, with changes propagated to the
+ back-end servers as needed. This option was implemented and works
+ well. Because the core pointer on a back-end controls the hardware
+ mouse on that back-end, core pointers cannot be treated as XInput
+ extension devices. However, all back-end XInput extensions devices
+ can be mapped to either DMX core or DMX XInput extension devices.
+</para>
+</listitem>
+
+<listitem>
+ <para>Console Input. The front-end server could create a console
+ window that is displayed on an X server independent of the back-end
+ X servers. This console window could display things like the
+ physical screen layout, and the front-end could get its core input
+ events from events delivered to the console window. This option was
+ implemented and works well. To help the human navigate, window
+ outlines are also displayed in the console window. Further, console
+ windows can be used as either core or XInput extension devices.
+</para>
+</listitem>
+
+<listitem>
+ <para>Other options were initially explored, but they were all
+ partial subsets of the options listed above and, hence, are
+ irrelevant.
+</para>
+</listitem>
+
+</orderedlist>
+</para>
+
+<para>Although extended input devices are not specifically mentioned in the
+Distributed X requirements, the options above were all implemented so
+that XInput extension devices were supported.
+</para>
+
+<para>The bootstrap code (Xdmx) had dummy input devices, and these are
+still supported in the final version. These do the necessary
+initialization to satisfy the X server's requirements for core pointer
+and keyboard devices, but no input events are ever generated.
+</para>
+
+<para>Status: The input code is complete. Because of the complexity of the
+XFree86 input device drivers (and their heavy reliance on XFree86
+infrastructure), separate low-level device drivers were implemented for
+Xdmx. The following kinds of drivers are supported (in general, the
+devices can be treated arbitrarily as "core" input devices or as XInput
+"extension" devices; and multiple instances of different kinds of
+devices can be simultaneously available):
+<orderedlist>
+<listitem>
+ <para> A "dummy" device drive that never generates events.
+</para>
+</listitem>
+
+<listitem>
+ <para> "Local" input is from the low-level hardware on which the
+ Xdmx binary is running. This is the only area where using the
+ XFree86 driver infrastructure would have been helpful, and then
+ only partially, since good support for generic USB devices does
+ not yet exist in XFree86 (in any case, XFree86 and kdrive driver
+ code was used where possible). Currently, the following local
+ devices are supported under Linux (porting to other operating
+ systems should be fairly straightforward):
+ <itemizedlist>
+ <listitem><para>Linux keyboard</para></listitem>
+ <listitem><para>Linux serial mouse (MS)</para></listitem>
+ <listitem><para>Linux PS/2 mouse</para></listitem>
+ <listitem><para>USB keyboard</para></listitem>
+ <listitem><para>USB mouse</para></listitem>
+ <listitem><para>USB generic device (e.g., joystick, gamepad, etc.)</para></listitem>
+ </itemizedlist>
+</para>
+</listitem>
+
+<listitem>
+ <para> "Backend" input is taken from one or more of the back-end
+ displays. In this case, events are taken from the back-end X
+ server and are converted to Xdmx events. Care must be taken so
+ that the sprite moves properly on the display from which input
+ is being taken.
+</para>
+</listitem>
+
+<listitem>
+ <para> "Console" input is taken from an X window that Xdmx
+ creates on the operator's display (i.e., on the machine running
+ the Xdmx binary). When the operator's mouse is inside the
+ console window, then those events are converted to Xdmx events.
+ Several special features are available: the console can display
+ outlines of windows that are on the Xdmx display (to facilitate
+ navigation), the cursor can be confined to the console, and a
+ "fine" mode can be activated to allow very precise cursor
+ positioning.
+</para>
+</listitem>
+</orderedlist>
+
+</para>
+
+</sect2>
+
+<!-- May 2002; July 2003 -->
+
+<sect2>
+<title>Output device handling</title>
+
+<para>The output of the DMX system displays rendering and windowing
+requests across multiple screens. The screens are typically arranged in
+a grid such that together they represent a single large display.
+</para>
+
+<para>The output section of the DMX code consists of two parts. The first
+is in the front-end proxy X server (Xdmx), which accepts client
+connections, manages the windows, and potentially renders primitives but
+does not actually display any of the drawing primitives. The second
+part is the back-end X server(s), which accept commands from the
+front-end server and display the results on their screens.
+</para>
+
+<sect3>
+<title>Initialization</title>
+
+<para>The DMX front-end must first initialize its screens by connecting to
+each of the back-end X servers and collecting information about each of
+these screens. However, the information collected from the back-end X
+servers might be inconsistent. Handling these cases can be difficult
+and/or inefficient. For example, a two screen system has one back-end X
+server running at 16bpp while the second is running at 32bpp.
+Converting rendering requests (e.g., XPutImage() or XGetImage()
+requests) to the appropriate bit depth can be very time consuming.
+Analyzing these cases to determine how or even if it is possible to
+handle them is required. The current Xinerama code handles many of
+these cases (e.g., in PanoramiXConsolidate()) and will be used as a
+starting point. In general, the best solution is to use homogeneous X
+servers and display devices. Using back-end servers with the same depth
+is a requirement of the final DMX implementation.
+</para>
+
+<para>Once this screen consolidation is finished, the relative position of
+each back-end X server's screen in the unified screen is initialized. A
+full-screen window is opened on each of the back-end X servers, and the
+cursor on each screen is turned off. The final DMX implementation can
+also make use of a partial-screen window, or multiple windows per
+back-end screen.
+</para>
+</sect3>
+
+<sect3>
+<title>Handling rendering requests</title>
+
+<para>After initialization, X applications connect to the front-end server.
+There are two possible implementations of how rendering and windowing
+requests are handled in the DMX system:
+
+<orderedlist>
+<listitem>
+ <para>A shadow framebuffer is used in the front-end server as the
+ render target. In this option, all protocol requests are completely
+ handled in the front-end server. All state and resources are
+ maintained in the front-end including a shadow copy of the entire
+ framebuffer. The framebuffers attached to the back-end servers are
+ updated by XPutImage() calls with data taken directly from the
+ shadow framebuffer.
+</para>
+
+ <para>This solution suffers from two main problems. First, it does not
+ take advantage of any accelerated hardware available in the system.
+ Second, the size of the XPutImage() calls can be quite large and
+ thus will be limited by the bandwidth available.
+</para>
+
+ <para>The initial DMX implementation used a shadow framebuffer by
+ default.
+</para>
+</listitem>
+
+<listitem>
+ <para>Rendering requests are sent to each back-end server for
+ handling (as is done in the Xnest server described above). In this
+ option, certain protocol requests are handled in the front-end
+ server and certain requests are repackaged and then sent to the
+ back-end servers. The framebuffer is distributed across the
+ multiple back-end servers. Rendering to the framebuffer is handled
+ on each back-end and can take advantage of any acceleration
+ available on the back-end servers' graphics display device. State
+ is maintained both in the front and back-end servers.
+</para>
+
+ <para>This solution suffers from two main drawbacks. First, protocol
+ requests are sent to all back-end servers -- even those that will
+ completely clip the rendering primitive -- which wastes bandwidth
+ and processing time. Second, state is maintained both in the front-
+ and back-end servers. These drawbacks are not as severe as in
+ option 1 (above) and can either be overcome through optimizations or
+ are acceptable. Therefore, this option will be used in the final
+ implementation.
+</para>
+
+ <para>The final DMX implementation defaults to this mechanism, but also
+ supports the shadow framebuffer mechanism. Several optimizations
+ were implemented to eliminate the drawbacks of the default
+ mechanism. These optimizations are described the section below and
+ in Phase II of the Development Results (see appendix).
+</para>
+</listitem>
+
+</orderedlist>
+</para>
+
+<para>Status: Both the shadow framebuffer and Xnest-style code is complete.
+<!-- May 2002 -->
+</para>
+
+</sect3>
+</sect2>
+
+<sect2>
+<title>Optimizing DMX</title>
+
+<para>Initially, the Xnest-style solution's performance will be measured
+and analyzed to determine where the performance bottlenecks exist.
+There are four main areas that will be addressed.
+</para>
+
+<para>First, to obtain reasonable interactivity with the first development
+phase, XSync() was called after each protocol request. The XSync()
+function flushes any pending protocol requests. It then waits for the
+back-end to process the request and send a reply that the request has
+completed. This happens with each back-end server and performance
+greatly suffers. As a result of the way XSync() is called in the first
+development phase, the batching that the X11 library performs is
+effectively defeated. The XSync() call usage will be analyzed and
+optimized by batching calls and performing them at regular intervals,
+except where interactivity will suffer (e.g., on cursor movements).
+</para>
+
+<para>Second, the initial Xnest-style solution described above sends the
+repackaged protocol requests to all back-end servers regardless of
+whether or not they would be completely clipped out. The requests that
+are trivially rejected on the back-end server wastes the limited
+bandwidth available. By tracking clipping changes in the DMX X server's
+windowing code (e.g., by opening, closing, moving or resizing windows),
+we can determine whether or not back-end windows are visible so that
+trivial tests in the front-end server's GC ops drawing functions can
+eliminate these unnecessary protocol requests.
+</para>
+
+<para>Third, each protocol request will be analyzed to determine if it is
+possible to break the request into smaller pieces at display boundaries.
+The initial ones to be analyzed are put and get image requests since
+they will require the greatest bandwidth to transmit data between the
+front and back-end servers. Other protocol requests will be analyzed
+and those that will benefit from breaking them into smaller requests
+will be implemented.
+</para>
+
+<para>Fourth, an extension is being considered that will allow font glyphs to
+be transferred from the front-end DMX X server to each back-end server.
+This extension will permit the front-end to handle all font requests and
+eliminate the requirement that all back-end X servers share the exact
+same fonts as the front-end server. We are investigating the
+feasibility of this extension during this development phase.
+</para>
+
+<para>Other potential optimizations will be determined from the performance
+analysis.
+</para>
+
+<para>Please note that in our initial design, we proposed optimizing BLT
+operations (e.g., XCopyArea() and window moves) by developing an
+extension that would allow individual back-end servers to directly copy
+pixel data to other back-end servers. This potential optimization was
+in response to the simple image movement implementation that required
+potentially many calls to GetImage() and PutImage(). However, the
+current Xinerama implementation handles these BLT operations
+differently. Instead of copying data to and from screens, they generate
+expose events -- just as happens in the case when a window is moved from
+off a screen to on screen. This approach saves the limited bandwidth
+available between front and back-end servers and is being standardized
+with Xinerama. It also eliminates the potential setup problems and
+security issues resulting from having each back-end server open
+connections to all other back-end servers. Therefore, we suggest
+accepting Xinerama's expose event solution.
+</para>
+
+<para>Also note that the approach proposed in the second and third
+optimizations might cause backing store algorithms in the back-end to be
+defeated, so a DMX X server configuration flag will be added to disable
+these optimizations.
+</para>
+
+<para>Status: The optimizations proposed above are complete. It was
+determined that the using the xfs font server was sufficient and
+creating a new mechanism to pass glyphs was redundant; therefore, the
+fourth optimization proposed above was not included in DMX.
+<!-- September 2002 -->
+</para>
+
+</sect2>
+
+<sect2>
+<title>DMX X extension support</title>
+
+<para>The DMX X server keeps track of all the windowing information on the
+back-end X servers, but does not currently export this information to
+any client applications. An extension will be developed to pass the
+screen information and back-end window IDs to DMX-aware clients. These
+clients can then use this information to directly connect to and render
+to the back-end windows. Bypassing the DMX X server allows DMX-aware
+clients to break up complex rendering requests on their own and send
+them directly to the windows on the back-end server's screens. An
+example of a client that can make effective use of this extension is
+Chromium.
+</para>
+
+<para>Status: The extension, as implemented, is fully documented in
+"Client-to-Server DMX Extension to the X Protocol". Future changes
+might be required based on feedback and other proposed enhancements to
+DMX. Currently, the following facilities are supported:
+<orderedlist>
+<listitem><para>
+ Screen information (clipping rectangle for each screen relative
+ to the virtual screen)
+</para></listitem>
+<listitem><para>
+ Window information (window IDs and clipping information for each
+ back-end window that corresponds to each DMX window)
+</para></listitem>
+<listitem><para>
+ Input device information (mappings from DMX device IDs to
+ back-end device IDs)
+</para></listitem>
+<listitem><para>
+ Force window creation (so that a client can override the
+ server-side lazy window creation optimization)
+</para></listitem>
+<listitem><para>
+ Reconfiguration (so that a client can request that a screen
+ position be changed)
+</para></listitem>
+<listitem><para>
+ Addition and removal of back-end servers and back-end and
+ console inputs.
+</para></listitem>
+</orderedlist>
+</para>
+<!-- September 2002; July 2003 -->
+
+</sect2>
+
+<sect2>
+<title>Common X extension support</title>
+
+<para>The XInput, XKeyboard and Shape extensions are commonly used
+extensions to the base X11 protocol. XInput allows multiple and
+non-standard input devices to be accessed simultaneously. These input
+devices can be connected to either the front-end or back-end servers.
+XKeyboard allows much better keyboard mappings control. Shape adds
+support for arbitrarily shaped windows and is used by various window
+managers. Nearly all potential back-end X servers make these extensions
+available, and support for each one will be added to the DMX system.
+</para>
+
+<para>In addition to the extensions listed above, support for the X
+Rendering extension (Render) is being developed. Render adds digital
+image composition to the rendering model used by the X Window System.
+While this extension is still under development by Keith Packard of HP,
+support for the current version will be added to the DMX system.
+</para>
+
+<para>Support for the XTest extension was added during the first
+development phase.
+</para>
+
+<!-- WARNING: this list is duplicated in the Phase IV discussion -->
+<para>Status: The following extensions are supported and are discussed in
+more detail in Phase IV of the Development Results (see appendix):
+ BIG-REQUESTS,
+ DEC-XTRAP,
+ DMX,
+ DPMS,
+ Extended-Visual-Information,
+ GLX,
+ LBX,
+ RECORD,
+ RENDER,
+ SECURITY,
+ SHAPE,
+ SYNC,
+ X-Resource,
+ XC-APPGROUP,
+ XC-MISC,
+ XFree86-Bigfont,
+ XINERAMA,
+ XInputExtension,
+ XKEYBOARD, and
+ XTEST.
+<!-- November 2002; updated February 2003, July 2003 -->
+</para>
+</sect2>
+
+<sect2>
+<title>OpenGL support</title>
+
+<para>OpenGL support using the Mesa code base exists in XFree86 release 4
+and later. Currently, the direct rendering infrastructure (DRI)
+provides accelerated OpenGL support for local clients and unaccelerated
+OpenGL support (i.e., software rendering) is provided for non-local
+clients.
+</para>
+
+<para>The single head OpenGL support in XFree86 4.x will be extended to use
+the DMX system. When the front and back-end servers are on the same
+physical hardware, it is possible to use the DRI to directly render to
+the back-end servers. First, the existing DRI will be extended to
+support multiple display heads, and then to support the DMX system.
+OpenGL rendering requests will be direct rendering to each back-end X
+server. The DRI will request the screen layout (either from the
+existing Xinerama extension or a DMX-specific extension). Support for
+synchronized swap buffers will also be added (on hardware that supports
+it). Note that a single front-end server with a single back-end server
+on the same physical machine can emulate accelerated indirect rendering.
+</para>
+
+<para>When the front and back-end servers are on different physical
+hardware or are using non-XFree86 4.x X servers, a mechanism to render
+primitives across the back-end servers will be provided. There are
+several options as to how this can be implemented.
+</para>
+
+<orderedlist>
+<listitem>
+ <para>The existing OpenGL support in each back-end server can be
+ used by repackaging rendering primitives and sending them to each
+ back-end server. This option is similar to the unoptimized
+ Xnest-style approach mentioned above. Optimization of this solution
+ is beyond the scope of this project and is better suited to other
+ distributed rendering systems.
+</para></listitem>
+
+<listitem>
+ <para>Rendering to a pixmap in the front-end server using the
+ current XFree86 4.x code, and then displaying to the back-ends via
+ calls to XPutImage() is another option. This option is similar to
+ the shadow frame buffer approach mentioned above. It is slower and
+ bandwidth intensive, but has the advantage that the back-end servers
+ are not required to have OpenGL support.
+</para></listitem>
+</orderedlist>
+
+<para>These, and other, options will be investigated in this phase of the
+work.
+</para>
+
+<para>Work by others have made Chromium DMX-aware. Chromium will use the
+DMX X protocol extension to obtain information about the back-end
+servers and will render directly to those servers, bypassing DMX.
+</para>
+
+<para>Status: OpenGL support by the glxProxy extension was implemented by
+SGI and has been integrated into the DMX code base.
+</para>
+<!-- May 2003-->
+</sect2>
+
+</sect1>
+
+<!-- ============================================================ -->
+<sect1>
+<title>Current issues</title>
+
+<para>In this sections the current issues are outlined that require further
+investigation.
+</para>
+
+<sect2>
+<title>Fonts</title>
+
+<para>The font path and glyphs need to be the same for the front-end and
+each of the back-end servers. Font glyphs could be sent to the back-end
+servers as necessary but this would consume a significant amount of
+available bandwidth during font rendering for clients that use many
+different fonts (e.g., Netscape). Initially, the font server (xfs) will
+be used to provide the fonts to both the front-end and back-end servers.
+Other possibilities will be investigated during development.
+</para>
+</sect2>
+
+<sect2>
+<title>Zero width rendering primitives</title>
+
+<para>To allow pixmap and on-screen rendering to be pixel perfect, all
+back-end servers must render zero width primitives exactly the same as
+the front-end renders the primitives to pixmaps. For those back-end
+servers that do not exactly match, zero width primitives will be
+automatically converted to one width primitives. This can be handled in
+the front-end server via the GC state.
+</para>
+</sect2>
+
+<sect2>
+<title>Output scaling</title>
+
+<para>With very large tiled displays, it might be difficult to read the
+information on the standard X desktop. In particular, the cursor can be
+easily lost and fonts could be difficult to read. Automatic primitive
+scaling might prove to be very useful. We will investigate the
+possibility of scaling the cursor and providing a set of alternate
+pre-scaled fonts to replace the standard fonts that many applications
+use (e.g., fixed). Other options for automatic scaling will also be
+investigated.
+</para>
+</sect2>
+
+<sect2>
+<title>Per-screen colormaps</title>
+
+<para>Each screen's default colormap in the set of back-end X servers
+should be able to be adjusted via a configuration utility. This support
+is would allow the back-end screens to be calibrated via custom gamma
+tables. On 24-bit systems that support a DirectColor visual, this type
+of correction can be accommodated. One possible implementation would be
+to advertise to X client of the DMX server a TrueColor visual while
+using DirectColor visuals on the back-end servers to implement this type
+of color correction. Other options will be investigated.
+</para>
+</sect2>
+</sect1>
+
+<!-- ============================================================ -->
+<appendix>
+<title>Appendix</title>
+
+<sect1>
+<title>Background</title>
+
+<para>This section describes the existing Open Source architectures that
+can be used to handle multiple screens and upon which this development
+project is based. This section was written before the implementation
+was finished, and may not reflect actual details of the implementation.
+It is left for historical interest only.
+</para>
+
+<sect2>
+<title>Core input device handling</title>
+
+<para>The following is a description of how core input devices are handled
+by an X server.
+</para>
+
+<sect3>
+<title>InitInput()</title>
+
+<para>InitInput() is a DDX function that is called at the start of each
+server generation from the X server's main() function. Its purpose is
+to determine what input devices are connected to the X server, register
+them with the DIX and MI layers, and initialize the input event queue.
+InitInput() does not have a return value, but the X server will abort if
+either a core keyboard device or a core pointer device are not
+registered. Extended input (XInput) devices can also be registered in
+InitInput().
+</para>
+
+<para>InitInput() usually has implementation specific code to determine
+which input devices are available. For each input device it will be
+using, it calls AddInputDevice():
+
+<variablelist>
+<varlistentry>
+<term>AddInputDevice()</term>
+<listitem><para>This DIX function allocates the device structure,
+registers a callback function (which handles device init, close, on and
+off), and returns the input handle, which can be treated as opaque. It
+is called once for each input device.
+</para></listitem>
+</varlistentry>
+</variablelist>
+</para>
+
+<para>Once input handles for core keyboard and core pointer devices have
+been obtained from AddInputDevice(), they are registered as core devices
+by calling RegisterPointerDevice() and RegisterKeyboardDevice(). Each
+of these should be called once. If both core devices are not
+registered, then the X server will exit with a fatal error when it
+attempts to start the input devices in InitAndStartDevices(), which is
+called directly after InitInput() (see below).
+
+<variablelist>
+<varlistentry>
+<term>Register{Pointer,Keyboard}Device()</term>
+<listitem><para>These DIX functions take a
+handle returned from AddInputDevice() and initialize the core input
+device fields in inputInfo, and initialize the input processing and grab
+functions for each core input device.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>The core pointer device is then registered with the miPointer code
+(which does the high level cursor handling). While this registration
+is not necessary for correct miPointer operation in the current XFree86
+code, it is still done mostly for compatibility reasons.
+</para>
+
+<para><variablelist>
+
+<varlistentry>
+<term>miRegisterPointerDevice()</term>
+<listitem><para>This MI function registers the core
+pointer's input handle with with the miPointer code.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>The final part of InitInput() is the initialization of the input
+event queue handling. In most cases, the event queue handling provided
+in the MI layer is used. The primary XFree86 X server uses its own
+event queue handling to support some special cases related to the XInput
+extension and the XFree86-specific DGA extension. For our purposes, the
+MI event queue handling should be suitable. It is initialized by
+calling mieqInit():
+
+<variablelist>
+<varlistentry>
+<term>mieqInit()</term>
+<listitem><para>This MI function initializes the MI event queue for the
+core devices, and is passed the public component of the input handles
+for the two core devices.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>If a wakeup handler is required to deliver synchronous input
+events, it can be registered here by calling the DIX function
+RegisterBlockAndWakeupHandlers(). (See the devReadInput() description
+below.)
+</para>
+</sect3>
+
+<sect3>
+<title>InitAndStartDevices()</title>
+
+<para>InitAndStartDevices() is a DIX function that is called immediately
+after InitInput() from the X server's main() function. Its purpose is
+to initialize each input device that was registered with
+AddInputDevice(), enable each input device that was successfully
+initialized, and create the list of enabled input devices. Once each
+registered device is processed in this way, the list of enabled input
+devices is checked to make sure that both a core keyboard device and
+core pointer device were registered and successfully enabled. If not,
+InitAndStartDevices() returns failure, and results in the the X server
+exiting with a fatal error.
+</para>
+
+<para>Each registered device is initialized by calling its callback
+(dev->deviceProc) with the DEVICE_INIT argument:
+
+<variablelist>
+<varlistentry>
+<term>(*dev->deviceProc)(dev, DEVICE_INIT)</term>
+<listitem>
+<para>This function initializes the
+device structs with core information relevant to the device.
+</para>
+
+<para>For pointer devices, this means specifying the number of buttons,
+default button mapping, the function used to get motion events (usually
+miPointerGetMotionEvents()), the function used to change/control the
+core pointer motion parameters (acceleration and threshold), and the
+motion buffer size.
+</para>
+
+<para>For keyboard devices, this means specifying the keycode range,
+default keycode to keysym mapping, default modifier mapping, and the
+functions used to sound the keyboard bell and modify/control the
+keyboard parameters (LEDs, bell pitch and duration, key click, which
+keys are auto-repeating, etc).
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>Each initialized device is enabled by calling EnableDevice():
+
+<variablelist>
+<varlistentry>
+<term>EnableDevice()</term>
+<listitem>
+<para>EnableDevice() calls the device callback with
+DEVICE_ON:
+ <variablelist>
+ <varlistentry>
+ <term>(*dev->deviceProc)(dev, DEVICE_ON)</term>
+ <listitem>
+ <para>This typically opens and
+ initializes the relevant physical device, and when appropriate,
+ registers the device's file descriptor (or equivalent) as a valid
+ input source.
+ </para></listitem></varlistentry>
+ </variablelist>
+ </para>
+
+ <para>EnableDevice() then adds the device handle to the X server's
+ global list of enabled devices.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>InitAndStartDevices() then verifies that a valid core keyboard and
+pointer has been initialized and enabled. It returns failure if either
+are missing.
+</para>
+</sect3>
+
+<sect3>
+<title>devReadInput()</title>
+
+<para>Each device will have some function that gets called to read its
+physical input. These may be called in a number of different ways. In
+the case of synchronous I/O, they will be called from a DDX
+wakeup-handler that gets called after the server detects that new input is
+available. In the case of asynchronous I/O, they will be called from a
+(SIGIO) signal handler triggered when new input is available. This
+function should do at least two things: make sure that input events get
+enqueued, and make sure that the cursor gets moved for motion events
+(except if these are handled later by the driver's own event queue
+processing function, which cannot be done when using the MI event queue
+handling).
+</para>
+
+<para>Events are queued by calling mieqEnqueue():
+
+<variablelist>
+<varlistentry>
+<term>mieqEnqueue()</term>
+<listitem>
+<para>This MI function is used to add input events to the
+event queue. It is simply passed the event to be queued.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>The cursor position should be updated when motion events are
+enqueued, by calling either miPointerAbsoluteCursor() or
+miPointerDeltaCursor():
+
+<variablelist>
+<varlistentry>
+<term>miPointerAbsoluteCursor()</term>
+<listitem>
+<para>This MI function is used to move the
+cursor to the absolute coordinates provided.
+</para></listitem></varlistentry>
+<varlistentry>
+<term>miPointerDeltaCursor()</term>
+<listitem>
+<para>This MI function is used to move the cursor
+relative to its current position.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+</sect3>
+
+<sect3>
+<title>ProcessInputEvents()</title>
+
+<para>ProcessInputEvents() is a DDX function that is called from the X
+server's main dispatch loop when new events are available in the input
+event queue. It typically processes the enqueued events, and updates
+the cursor/pointer position. It may also do other DDX-specific event
+processing.
+</para>
+
+<para>Enqueued events are processed by mieqProcessInputEvents() and passed
+to the DIX layer for transmission to clients:
+
+<variablelist>
+<varlistentry>
+<term>mieqProcessInputEvents()</term>
+<listitem>
+<para>This function processes each event in the
+event queue, and passes it to the device's input processing function.
+The DIX layer provides default functions to do this processing, and they
+handle the task of getting the events passed back to the relevant
+clients.
+</para></listitem></varlistentry>
+<varlistentry>
+<term>miPointerUpdate()</term>
+<listitem>
+<para>This function resynchronized the cursor position
+with the new pointer position. It also takes care of moving the cursor
+between screens when needed in multi-head configurations.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+</sect3>
+
+<sect3>
+<title>DisableDevice()</title>
+
+<para>DisableDevice is a DIX function that removes an input device from the
+list of enabled devices. The result of this is that the device no
+longer generates input events. The device's data structures are kept in
+place, and disabling a device like this can be reversed by calling
+EnableDevice(). DisableDevice() may be called from the DDX when it is
+desirable to do so (e.g., the XFree86 server does this when VT
+switching). Except for special cases, this is not normally called for
+core input devices.
+</para>
+
+<para>DisableDevice() calls the device's callback function with
+<constant>DEVICE_OFF</constant>:
+
+<variablelist>
+<varlistentry>
+<term>(*dev->deviceProc)(dev, DEVICE_OFF)</term>
+<listitem>
+<para>This typically closes the
+relevant physical device, and when appropriate, unregisters the device's
+file descriptor (or equivalent) as a valid input source.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>DisableDevice() then removes the device handle from the X server's
+global list of enabled devices.
+</para>
+
+</sect3>
+
+<sect3>
+<title>CloseDevice()</title>
+
+<para>CloseDevice is a DIX function that removes an input device from the
+list of available devices. It disables input from the device and frees
+all data structures associated with the device. This function is
+usually called from CloseDownDevices(), which is called from main() at
+the end of each server generation to close all input devices.
+</para>
+
+<para>CloseDevice() calls the device's callback function with
+<constant>DEVICE_CLOSE</constant>:
+
+<variablelist>
+<varlistentry>
+<term>(*dev->deviceProc)(dev, DEVICE_CLOSE)</term>
+<listitem>
+<para>This typically closes the
+relevant physical device, and when appropriate, unregisters the device's
+file descriptor (or equivalent) as a valid input source. If any device
+specific data structures were allocated when the device was initialized,
+they are freed here.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>CloseDevice() then frees the data structures that were allocated
+for the device when it was registered/initialized.
+</para>
+
+</sect3>
+
+<sect3>
+<title>LegalModifier()</title>
+<!-- dmx/dmxinput.c - currently returns TRUE -->
+<para>LegalModifier() is a required DDX function that can be used to
+restrict which keys may be modifier keys. This seems to be present for
+historical reasons, so this function should simply return TRUE
+unconditionally.
+</para>
+
+</sect3>
+</sect2>
+
+<sect2>
+<title>Output handling</title>
+
+<para>The following sections describe the main functions required to
+initialize, use and close the output device(s) for each screen in the X
+server.
+</para>
+
+<sect3>
+<title>InitOutput()</title>
+
+<para>This DDX function is called near the start of each server generation
+from the X server's main() function. InitOutput()'s main purpose is to
+initialize each screen and fill in the global screenInfo structure for
+each screen. It is passed three arguments: a pointer to the screenInfo
+struct, which it is to initialize, and argc and argv from main(), which
+can be used to determine additional configuration information.
+</para>
+
+<para>The primary tasks for this function are outlined below:
+
+<orderedlist>
+<listitem>
+ <para><emphasis remap="bf">Parse configuration info:</emphasis> The first task of InitOutput()
+ is to parses any configuration information from the configuration
+ file. In addition to the XF86Config file, other configuration
+ information can be taken from the command line. The command line
+ options can be gathered either in InitOutput() or earlier in the
+ ddxProcessArgument() function, which is called by
+ ProcessCommandLine(). The configuration information determines the
+ characteristics of the screen(s). For example, in the XFree86 X
+ server, the XF86Config file specifies the monitor information, the
+ screen resolution, the graphics devices and slots in which they are
+ located, and, for Xinerama, the screens' layout.
+</para>
+</listitem>
+
+<listitem>
+ <para><emphasis remap="bf">Initialize screen info:</emphasis> The next task is to initialize
+ the screen-dependent internal data structures. For example, part of
+ what the XFree86 X server does is to allocate its screen and pixmap
+ private indices, probe for graphics devices, compare the probed
+ devices to the ones listed in the XF86Config file, and add the ones that
+ match to the internal xf86Screens[] structure.
+</para>
+</listitem>
+
+<listitem>
+ <para><emphasis remap="bf">Set pixmap formats:</emphasis> The next task is to initialize the
+ screenInfo's image byte order, bitmap bit order and bitmap scanline
+ unit/pad. The screenInfo's pixmap format's depth, bits per pixel
+ and scanline padding is also initialized at this stage.
+</para>
+</listitem>
+
+<listitem>
+ <para><emphasis remap="bf">Unify screen info:</emphasis> An optional task that might be done at
+ this stage is to compare all of the information from the various
+ screens and determines if they are compatible (i.e., if the set of
+ screens can be unified into a single desktop). This task has
+ potential to be useful to the DMX front-end server, if Xinerama's
+ PanoramiXConsolidate() function is not sufficient.
+</para>
+</listitem>
+</orderedlist>
+</para>
+
+<para>Once these tasks are complete, the valid screens are known and each
+of these screens can be initialized by calling AddScreen().
+</para>
+</sect3>
+
+<sect3>
+<title>AddScreen()</title>
+
+<para>This DIX function is called from InitOutput(), in the DDX layer, to
+add each new screen to the screenInfo structure. The DDX screen
+initialization function and command line arguments (i.e., argc and argv)
+are passed to it as arguments.
+</para>
+
+<para>This function first allocates a new Screen structure and any privates
+that are required. It then initializes some of the fields in the Screen
+struct and sets up the pixmap padding information. Finally, it calls
+the DDX screen initialization function ScreenInit(), which is described
+below. It returns the number of the screen that were just added, or -1
+if there is insufficient memory to add the screen or if the DDX screen
+initialization fails.
+</para>
+</sect3>
+
+<sect3>
+<title>ScreenInit()</title>
+
+<para>This DDX function initializes the rest of the Screen structure with
+either generic or screen-specific functions (as necessary). It also
+fills in various screen attributes (e.g., width and height in
+millimeters, black and white pixel values).
+</para>
+
+<para>The screen init function usually calls several functions to perform
+certain screen initialization functions. They are described below:
+
+<variablelist>
+<varlistentry>
+<term>{mi,*fb}ScreenInit()</term>
+<listitem>
+<para>The DDX layer's ScreenInit() function usually
+calls another layer's ScreenInit() function (e.g., miScreenInit() or
+fbScreenInit()) to initialize the fallbacks that the DDX driver does not
+specifically handle.
+</para>
+
+<para>After calling another layer's ScreenInit() function, any
+screen-specific functions either wrap or replace the other layer's
+function pointers. If a function is to be wrapped, each of the old
+function pointers from the other layer are stored in a screen private
+area. Common functions to wrap are CloseScreen() and SaveScreen().
+</para></listitem></varlistentry>
+
+<varlistentry>
+<term>miInitializeBackingStore()</term>
+<listitem>
+<para>This MI function initializes the
+screen's backing storage functions, which are used to save areas of
+windows that are currently covered by other windows.
+</para></listitem></varlistentry>
+
+<varlistentry>
+<term>miDCInitialize()</term>
+<listitem>
+<para>This MI function initializes the MI cursor
+display structures and function pointers. If a hardware cursor is used,
+the DDX layer's ScreenInit() function will wrap additional screen and
+the MI cursor display function pointers.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>Another common task for ScreenInit() function is to initialize the
+output device state. For example, in the XFree86 X server, the
+ScreenInit() function saves the original state of the video card and
+then initializes the video mode of the graphics device.
+</para>
+</sect3>
+
+<sect3>
+<title>CloseScreen()</title>
+
+<para>This function restores any wrapped screen functions (and in
+particular the wrapped CloseScreen() function) and restores the state of
+the output device to its original state. It should also free any
+private data it created during the screen initialization.
+</para>
+</sect3>
+
+<sect3>
+<title>GC operations</title>
+
+<para>When the X server is requested to render drawing primitives, it does
+so by calling drawing functions through the graphics context's operation
+function pointer table (i.e., the GCOps functions). These functions
+render the basic graphics operations such as drawing rectangles, lines,
+text or copying pixmaps. Default routines are provided either by the MI
+layer, which draws indirectly through a simple span interface, or by the
+framebuffer layers (e.g., CFB, MFB, FB), which draw directly to a
+linearly mapped frame buffer.
+</para>
+
+<para>To take advantage of special hardware on the graphics device,
+specific GCOps functions can be replaced by device specific code.
+However, many times the graphics devices can handle only a subset of the
+possible states of the GC, so during graphics context validation,
+appropriate routines are selected based on the state and capabilities of
+the hardware. For example, some graphics hardware can accelerate single
+pixel width lines with certain dash patterns. Thus, for dash patterns
+that are not supported by hardware or for width 2 or greater lines, the
+default routine is chosen during GC validation.
+</para>
+
+<para>Note that some pointers to functions that draw to the screen are
+stored in the Screen structure. They include GetImage(), GetSpans(),
+CopyWindow() and RestoreAreas().
+</para>
+</sect3>
+
+<sect3>
+<title>Xnest</title>
+
+<para>The Xnest X server is a special proxy X server that relays the X
+protocol requests that it receives to a ``real'' X server that then
+processes the requests and displays the results, if applicable. To the X
+applications, Xnest appears as if it is a regular X server. However,
+Xnest is both server to the X application and client of the real X
+server, which will actually handle the requests.
+</para>
+
+<para>The Xnest server implements all of the standard input and output
+initialization steps outlined above.
+</para>
+
+<para><variablelist>
+<varlistentry>
+<term>InitOutput()</term>
+<listitem>
+<para>Xnest takes its configuration information from
+command line arguments via ddxProcessArguments(). This information
+includes the real X server display to connect to, its default visual
+class, the screen depth, the Xnest window's geometry, etc. Xnest then
+connects to the real X server and gathers visual, colormap, depth and
+pixmap information about that server's display, creates a window on that
+server, which will be used as the root window for Xnest.
+</para>
+
+<para>Next, Xnest initializes its internal data structures and uses the
+data from the real X server's pixmaps to initialize its own pixmap
+formats. Finally, it calls AddScreen(xnestOpenScreen, argc, argv) to
+initialize each of its screens.
+</para></listitem></varlistentry>
+
+<varlistentry>
+<term>ScreenInit()</term>
+<listitem>
+<para>Xnest's ScreenInit() function is called
+xnestOpenScreen(). This function initializes its screen's depth and
+visual information, and then calls miScreenInit() to set up the default
+screen functions. It then calls miInitializeBackingStore() and
+miDCInitialize() to initialize backing store and the software cursor.
+Finally, it replaces many of the screen functions with its own
+functions that repackage and send the requests to the real X server to
+which Xnest is attached.
+</para></listitem></varlistentry>
+
+<varlistentry>
+<term>CloseScreen()</term>
+<listitem>
+<para>This function frees its internal data structure
+allocations. Since it replaces instead of wrapping screen functions,
+there are no function pointers to unwrap. This can potentially lead to
+problems during server regeneration.
+</para></listitem></varlistentry>
+
+<varlistentry>
+<term>GC operations</term>
+<listitem>
+<para>The GC operations in Xnest are very simple since
+they leave all of the drawing to the real X server to which Xnest is
+attached. Each of the GCOps takes the request and sends it to the
+real X server using standard Xlib calls. For example, the X
+application issues a XDrawLines() call. This function turns into a
+protocol request to Xnest, which calls the xnestPolylines() function
+through Xnest's GCOps function pointer table. The xnestPolylines()
+function is only a single line, which calls XDrawLines() using the same
+arguments that were passed into it. Other GCOps functions are very
+similar. Two exceptions to the simple GCOps functions described above
+are the image functions and the BLT operations.
+</para>
+
+<para>The image functions, GetImage() and PutImage(), must use a temporary
+image to hold the image to be put of the image that was just grabbed
+from the screen while it is in transit to the real X server or the
+client. When the image has been transmitted, the temporary image is
+destroyed.
+</para>
+
+<para>The BLT operations, CopyArea() and CopyPlane(), handle not only the
+copy function, which is the same as the simple cases described above,
+but also the graphics exposures that result when the GC's graphics
+exposure bit is set to True. Graphics exposures are handled in a helper
+function, xnestBitBlitHelper(). This function collects the exposure
+events from the real X server and, if any resulting in regions being
+exposed, then those regions are passed back to the MI layer so that it
+can generate exposure events for the X application.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>The Xnest server takes its input from the X server to which it is
+connected. When the mouse is in the Xnest server's window, keyboard and
+mouse events are received by the Xnest server, repackaged and sent back
+to any client that requests those events.
+</para>
+</sect3>
+
+<sect3>
+<title>Shadow framebuffer</title>
+
+<para>The most common type of framebuffer is a linear array memory that
+maps to the video memory on the graphics device. However, accessing
+that video memory over an I/O bus (e.g., ISA or PCI) can be slow. The
+shadow framebuffer layer allows the developer to keep the entire
+framebuffer in main memory and copy it back to video memory at regular
+intervals. It also has been extended to handle planar video memory and
+rotated framebuffers.
+</para>
+
+<para>There are two main entry points to the shadow framebuffer code:
+
+<variablelist>
+<varlistentry>
+<term>shadowAlloc(width, height, bpp)</term>
+<listitem>
+<para>This function allocates the in
+memory copy of the framebuffer of size width*height*bpp. It returns a
+pointer to that memory, which will be used by the framebuffer
+ScreenInit() code during the screen's initialization.
+</para></listitem></varlistentry>
+
+<varlistentry>
+<term>shadowInit(pScreen, updateProc, windowProc)</term>
+<listitem>
+<para>This function
+initializes the shadow framebuffer layer. It wraps several screen
+drawing functions, and registers a block handler that will update the
+screen. The updateProc is a function that will copy the damaged regions
+to the screen, and the windowProc is a function that is used when the
+entire linear video memory range cannot be accessed simultaneously so
+that only a window into that memory is available (e.g., when using the
+VGA aperture).
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+
+<para>The shadow framebuffer code keeps track of the damaged area of each
+screen by calculating the bounding box of all drawing operations that
+have occurred since the last screen update. Then, when the block handler
+is next called, only the damaged portion of the screen is updated.
+</para>
+
+<para>Note that since the shadow framebuffer is kept in main memory, all
+drawing operations are performed by the CPU and, thus, no accelerated
+hardware drawing operations are possible.
+</para>
+
+</sect3>
+</sect2>
+
+<sect2>
+<title>Xinerama</title>
+
+<para>Xinerama is an X extension that allows multiple physical screens
+controlled by a single X server to appear as a single screen. Although
+the extension allows clients to find the physical screen layout via
+extension requests, it is completely transparent to clients at the core
+X11 protocol level. The original public implementation of Xinerama came
+from Digital/Compaq. XFree86 rewrote it, filling in some missing pieces
+and improving both X11 core protocol compliance and performance. The
+Xinerama extension will be passing through X.Org's standardization
+process in the near future, and the sample implementation will be based
+on this rewritten version.
+</para>
+
+<para>The current implementation of Xinerama is based primarily in the DIX
+(device independent) and MI (machine independent) layers of the X
+server. With few exceptions the DDX layers do not need any changes to
+support Xinerama. X server extensions often do need modifications to
+provide full Xinerama functionality.
+</para>
+
+<para>The following is a code-level description of how Xinerama functions.
+</para>
+
+<para>Note: Because the Xinerama extension was originally called the
+PanoramiX extension, many of the Xinerama functions still have the
+PanoramiX prefix.
+</para>
+
+<variablelist>
+<varlistentry>
+<term>PanoramiXExtensionInit()</term>
+<listitem>
+ <para>PanoramiXExtensionInit() is a
+ device-independent extension function that is called at the start of
+ each server generation from InitExtensions(), which is called from
+ the X server's main() function after all output devices have been
+ initialized, but before any input devices have been initialized.
+ </para>
+
+ <para>PanoramiXNumScreens is set to the number of physical screens. If
+ only one physical screen is present, the extension is disabled, and
+ PanoramiXExtensionInit() returns without doing anything else.
+ </para>
+
+ <para>The Xinerama extension is registered by calling AddExtension().
+ </para>
+
+ <para>A local per-screen array of data structures
+ (panoramiXdataPtr[])
+ is allocated for each physical screen, and GC and Screen private
+ indexes are allocated, and both GC and Screen private areas are
+ allocated for each physical screen. These hold Xinerama-specific
+ per-GC and per-Screen data. Each screen's CreateGC and CloseScreen
+ functions are wrapped by XineramaCreateGC() and
+ XineramaCloseScreen() respectively. Some new resource classes are
+ created for Xinerama drawables and GCs, and resource types for
+ Xinerama windows, pixmaps and colormaps.
+ </para>
+
+ <para>A region (XineramaScreenRegions[i]) is initialized for each
+ physical screen, and single region (PanoramiXScreenRegion) is
+ initialized to be the union of the screen regions. The
+ panoramiXdataPtr[] array is also initialized with the size and
+ origin of each screen. The relative positioning information for the
+ physical screens is taken from the array
+ dixScreenOrigins[], which
+ the DDX layer must initialize in InitOutput(). The bounds of the
+ combined screen is also calculated (PanoramiXPixWidth and
+ PanoramiXPixHeight).
+ </para>
+
+ <para>The DIX layer has a list of function pointers
+ (ProcVector[]) that
+ holds the entry points for the functions that process core protocol
+ requests. The requests that Xinerama must intercept and break up
+ into physical screen-specific requests are wrapped. The original
+ set is copied to SavedProcVector[]. The types of requests
+ intercepted are Window requests, GC requests, colormap requests,
+ drawing requests, and some geometry-related requests. This wrapping
+ allows the bulk of the protocol request processing to be handled
+ transparently to the DIX layer. Some operations cannot be dealt with
+ in this way and are handled with Xinerama-specific code within the
+ DIX layer.
+ </para>
+</listitem></varlistentry>
+
+<varlistentry>
+<term>PanoramiXConsolidate()</term>
+<listitem>
+ <para>PanoramiXConsolidate() is a
+ device-independent extension function that is called directly from
+ the X server's main() function after extensions and input/output
+ devices have been initialized, and before the root windows are
+ defined and initialized.
+</para>
+
+ <para>This function finds the set of depths (PanoramiXDepths[]) and
+ visuals (PanoramiXVisuals[])
+ common to all of the physical screens.
+ PanoramiXNumDepths is set to the number of common depths, and
+ PanoramiXNumVisuals is set to the number of common visuals.
+ Resources are created for the single root window and the default
+ colormap. Each of these resources has per-physical screen entries.
+ </para>
+</listitem></varlistentry>
+
+<varlistentry>
+<term>PanoramiXCreateConnectionBlock()</term>
+<listitem>
+ <para>PanoramiXConsolidate() is a
+ device-independent extension function that is called directly from
+ the X server's main() function after the per-physical screen root
+ windows are created. It is called instead of the standard DIX
+ CreateConnectionBlock() function. If this function returns FALSE,
+ the X server exits with a fatal error. This function will return
+ FALSE if no common depths were found in PanoramiXConsolidate().
+ With no common depths, Xinerama mode is not possible.
+ </para>
+
+ <para>The connection block holds the information that clients get when
+ they open a connection to the X server. It includes information
+ such as the supported pixmap formats, number of screens and the
+ sizes, depths, visuals, default colormap information, etc, for each
+ of the screens (much of information that <command>xdpyinfo</command> shows). The
+ connection block is initialized with the combined single screen
+ values that were calculated in the above two functions.
+ </para>
+
+ <para>The Xinerama extension allows the registration of connection
+ block callback functions. The purpose of these is to allow other
+ extensions to do processing at this point. These callbacks can be
+ registered by calling XineramaRegisterConnectionBlockCallback() from
+ the other extension's ExtensionInit() function. Each registered
+ connection block callback is called at the end of
+ PanoramiXCreateConnectionBlock().
+ </para>
+</listitem></varlistentry>
+</variablelist>
+
+<sect3>
+<title>Xinerama-specific changes to the DIX code</title>
+
+<para>There are a few types of Xinerama-specific changes within the DIX
+code. The main ones are described here.
+</para>
+
+<para>Functions that deal with colormap or GC -related operations outside of
+the intercepted protocol requests have a test added to only do the
+processing for screen numbers > 0. This is because they are handled for
+the single Xinerama screen and the processing is done once for screen 0.
+</para>
+
+<para>The handling of motion events does some coordinate translation between
+the physical screen's origin and screen zero's origin. Also, motion
+events must be reported relative to the composite screen origin rather
+than the physical screen origins.
+</para>
+
+<para>There is some special handling for cursor, window and event processing
+that cannot (either not at all or not conveniently) be done via the
+intercepted protocol requests. A particular case is the handling of
+pointers moving between physical screens.
+</para>
+</sect3>
+
+<sect3>
+<title>Xinerama-specific changes to the MI code</title>
+
+<para>The only Xinerama-specific change to the MI code is in miSendExposures()
+to handle the coordinate (and window ID) translation for expose events.
+</para>
+</sect3>
+
+<sect3>
+<title>Intercepted DIX core requests</title>
+
+<para>Xinerama breaks up drawing requests for dispatch to each physical
+screen. It also breaks up windows into pieces for each physical screen.
+GCs are translated into per-screen GCs. Colormaps are replicated on
+each physical screen. The functions handling the intercepted requests
+take care of breaking the requests and repackaging them so that they can
+be passed to the standard request handling functions for each screen in
+turn. In addition, and to aid the repackaging, the information from
+many of the intercepted requests is used to keep up to date the
+necessary state information for the single composite screen. Requests
+(usually those with replies) that can be satisfied completely from this
+stored state information do not call the standard request handling
+functions.
+</para>
+
+</sect3>
+
+</sect2>
+
+</sect1>
+
+<!-- ============================================================ -->
+
+<sect1>
+<title>Development Results</title>
+
+<para>In this section the results of each phase of development are
+discussed. This development took place between approximately June 2001
+and July 2003.
+</para>
+
+<sect2>
+<title>Phase I</title>
+
+<para>The initial development phase dealt with the basic implementation
+including the bootstrap code, which used the shadow framebuffer, and the
+unoptimized implementation, based on an Xnest-style implementation.
+</para>
+
+<sect3>
+<title>Scope</title>
+
+<para>The goal of Phase I is to provide fundamental functionality that can
+act as a foundation for ongoing work:
+<orderedlist>
+<listitem>
+ <para>Develop the proxy X server
+ <itemizedlist>
+ <listitem>
+ <para>The proxy X server will operate on the X11 protocol and
+ relay requests as necessary to correctly perform the request.
+ </para></listitem>
+ <listitem>
+ <para>Work will be based on the existing work for Xinerama and
+ Xnest.
+ </para></listitem>
+ <listitem>
+ <para>Input events and windowing operations are handled in the
+ proxy server and rendering requests are repackaged and sent to
+ each of the back-end servers for display.
+ </para></listitem>
+ <listitem>
+ <para>The multiple screen layout (including support for
+ overlapping screens) will be user configurable via a
+ configuration file or through the configuration tool.
+ </para></listitem>
+ </itemizedlist>
+ </para></listitem>
+ <listitem>
+ <para>Develop graphical configuration tool
+ <itemizedlist>
+ <listitem>
+ <para>There will be potentially a large number of X servers to
+ configure into a single display. The tool will allow the user
+ to specify which servers are involved in the configuration and
+ how they should be laid out.
+ </para></listitem>
+ </itemizedlist>
+ </para></listitem>
+ <listitem>
+ <para>Pass the X Test Suite
+ <itemizedlist>
+ <listitem>
+ <para>The X Test Suite covers the basic X11 operations. All
+ tests known to succeed must correctly operate in the distributed
+ X environment.
+ </para></listitem>
+ </itemizedlist>
+ </para></listitem>
+</orderedlist>
+
+</para>
+
+<para>For this phase, the back-end X servers are assumed to be unmodified X
+servers that do not support any DMX-related protocol extensions; future
+optimization pathways are considered, but are not implemented; and the
+configuration tool is assumed to rely only on libraries in the X source
+tree (e.g., Xt).
+</para>
+</sect3>
+
+<sect3>
+<title>Results</title>
+
+<para>The proxy X server, Xdmx, was developed to distribute X11 protocol
+requests to the set of back-end X servers. It opens a window on each
+back-end server, which represents the part of the front-end's root
+window that is visible on that screen. It mirrors window, pixmap and
+other state in each back-end server. Drawing requests are sent to
+either windows or pixmaps on each back-end server. This code is based
+on Xnest and uses the existing Xinerama extension.
+</para>
+
+<para>Input events can be taken from (1) devices attached to the back-end
+server, (2) core devices attached directly to the Xdmx server, or (3)
+from a ``console'' window on another X server. Events for these devices
+are gathered, processed and delivered to clients attached to the Xdmx
+server.
+</para>
+
+<para>An intuitive configuration format was developed to help the user
+easily configure the multiple back-end X servers. It was defined (see
+grammar in Xdmx man page) and a parser was implemented that is used by
+the Xdmx server and by a standalone xdmxconfig utility. The parsing
+support was implemented such that it can be easily factored out of the X
+source tree for use with other tools (e.g., vdl). Support for
+converting legacy vdl-format configuration files to the DMX format is
+provided by the vdltodmx utility.
+</para>
+
+<para>Originally, the configuration file was going to be a subsection of
+XFree86's XF86Config file, but that was not possible since Xdmx is a
+completely separate X server. Thus, a separate config file format was
+developed. In addition, a graphical configuration
+tool, xdmxconfig, was developed to allow the user to create and arrange
+the screens in the configuration file. The <emphasis remap="bf">-configfile</emphasis> and <emphasis remap="bf">-config</emphasis>
+command-line options can be used to start Xdmx using a configuration
+file.
+</para>
+
+<para>An extension that enables remote input testing is required for the X
+Test Suite to function. During this phase, this extension (XTEST) was
+implemented in the Xdmx server. The results from running the X Test
+Suite are described in detail below.
+</para>
+</sect3>
+
+<sect3>
+<title>X Test Suite</title>
+
+ <sect4>
+ <title>Introduction</title>
+ <para>
+ The X Test Suite contains tests that verify Xlib functions
+ operate correctly. The test suite is designed to run on a
+ single X server; however, since X applications will not be
+ able to tell the difference between the DMX server and a
+ standard X server, the X Test Suite should also run on the
+ DMX server.
+ </para>
+ <para>
+ The Xdmx server was tested with the X Test Suite, and the
+ existing failures are noted in this section. To put these
+ results in perspective, we first discuss expected X Test
+ failures and how errors in underlying systems can impact
+ Xdmx test results.
+ </para>
+ </sect4>
+
+ <sect4>
+ <title>Expected Failures for a Single Head</title>
+ <para>
+ A correctly implemented X server with a single screen is
+ expected to fail certain X Test tests. The following
+ well-known errors occur because of rounding error in the X
+ server code:
+ <literallayout>
+XDrawArc: Tests 42, 63, 66, 73
+XDrawArcs: Tests 45, 66, 69, 76
+ </literallayout>
+ </para>
+ <para>
+ The following failures occur because of the high-level X
+ server implementation:
+ <literallayout>
+XLoadQueryFont: Test 1
+XListFontsWithInfo: Tests 3, 4
+XQueryFont: Tests 1, 2
+ </literallayout>
+ </para>
+ <para>
+ The following test fails when running the X server as root
+ under Linux because of the way directory modes are
+ interpreted:
+ <literallayout>
+XWriteBitmapFile: Test 3
+ </literallayout>
+ </para>
+ <para>
+ Depending on the video card used for the back-end, other
+ failures may also occur because of bugs in the low-level
+ driver implementation. Over time, failures of this kind
+ are usually fixed by XFree86, but will show up in Xdmx
+ testing until then.
+ </para>
+ </sect4>
+
+ <sect4>
+ <title>Expected Failures for Xinerama</title>
+ <para>
+ Xinerama fails several X Test Suite tests because of
+ design decisions made for the current implementation of
+ Xinerama. Over time, many of these errors will be
+ corrected by XFree86 and the group working on a new
+ Xinerama implementation. Therefore, Xdmx will also share
+ X Suite Test failures with Xinerama.
+ </para>
+
+ <para>
+ We may be able to fix or work-around some of these
+ failures at the Xdmx level, but this will require
+ additional exploration that was not part of Phase I.
+ </para>
+
+ <para>
+ Xinerama is constantly improving, and the list of
+ Xinerama-related failures depends on XFree86 version and
+ the underlying graphics hardware. We tested with a
+ variety of hardware, including nVidia, S3, ATI Radeon,
+ and Matrox G400 (in dual-head mode). The list below
+ includes only those failures that appear to be from the
+ Xinerama layer, and does not include failures listed in
+ the previous section, or failures that appear to be from
+ the low-level graphics driver itself:
+ </para>
+
+ <para>
+ These failures were noted with multiple Xinerama
+ configurations:
+ <literallayout>
+XCopyPlane: Tests 13, 22, 31 (well-known Xinerama implementation issue)
+XSetFontPath: Test 4
+XGetDefault: Test 5
+XMatchVisualInfo: Test 1
+ </literallayout>
+ </para>
+ <para>
+ These failures were noted only when using one dual-head
+ video card with a 4.2.99.x XFree86 server:
+ <literallayout>
+XListPixmapFormats: Test 1
+XDrawRectangles: Test 45
+ </literallayout>
+ </para>
+ <para>
+ These failures were noted only when using two video cards
+ from different vendors with a 4.1.99.x XFree86 server:
+ <literallayout>
+XChangeWindowAttributes: Test 32
+XCreateWindow: Test 30
+XDrawLine: Test 22
+XFillArc: Test 22
+XChangeKeyboardControl: Tests 9, 10
+XRebindKeysym: Test 1
+ </literallayout>
+ </para>
+ </sect4>
+
+ <sect4>
+ <title>Additional Failures from Xdmx</title>
+
+ <para>
+ When running Xdmx, no unexpected failures were noted.
+ Since the Xdmx server is based on Xinerama, we expect to
+ have most of the Xinerama failures present in the Xdmx
+ server. Similarly, since the Xdmx server must rely on the
+ low-level device drivers on each back-end server, we also
+ expect that Xdmx will exhibit most of the back-end
+ failures. Here is a summary:
+ <literallayout>
+XListPixmapFormats: Test 1 (configuration dependent)
+XChangeWindowAttributes: Test 32
+XCreateWindow: Test 30
+XCopyPlane: Test 13, 22, 31
+XSetFontPath: Test 4
+XGetDefault: Test 5 (configuration dependent)
+XMatchVisualInfo: Test 1
+XRebindKeysym: Test 1 (configuration dependent)
+ </literallayout>
+ </para>
+ <para>
+ Note that this list is shorter than the combined list for
+ Xinerama because Xdmx uses different code paths to perform
+ some Xinerama operations. Further, some Xinerama failures
+ have been fixed in the XFree86 4.2.99.x CVS repository.
+ </para>
+ </sect4>
+
+ <sect4>
+ <title>Summary and Future Work</title>
+
+ <para>
+ Running the X Test Suite on Xdmx does not produce any
+ failures that cannot be accounted for by the underlying
+ Xinerama subsystem used by the front-end or by the
+ low-level device-driver code running on the back-end X
+ servers. The Xdmx server therefore is as ``correct'' as
+ possible with respect to the standard set of X Test Suite
+ tests.
+ </para>
+
+ <para>
+ During the following phases, we will continue to verify
+ Xdmx correctness using the X Test Suite. We may also use
+ other tests suites or write additional tests that run
+ under the X Test Suite that specifically verify the
+ expected behavior of DMX.
+ </para>
+ </sect4>
+</sect3>
+
+<sect3>
+<title>Fonts</title>
+
+<para>In Phase I, fonts are handled directly by both the front-end and the
+back-end servers, which is required since we must treat each back-end
+server during this phase as a ``black box''. What this requires is that
+<emphasis remap="bf">the front- and back-end servers must share the exact same font
+path</emphasis>. There are two ways to help make sure that all servers share the
+same font path:
+
+<orderedlist>
+ <listitem>
+ <para>First, each server can be configured to use the same font
+ server. The font server, xfs, can be configured to serve fonts to
+ multiple X servers via TCP.
+ </para></listitem>
+
+ <listitem>
+ <para>Second, each server can be configured to use the same font
+ path and either those font paths can be copied to each back-end
+ machine or they can be mounted (e.g., via NFS) on each back-end
+ machine.
+ </para></listitem>
+</orderedlist>
+</para>
+
+<para>One additional concern is that a client program can set its own font
+path, and if it does so, then that font path must be available on each
+back-end machine.
+</para>
+
+<para>The -fontpath command line option was added to allow users to
+initialize the font path of the front end server. This font path is
+propagated to each back-end server when the default font is loaded. If
+there are any problems, an error message is printed, which will describe
+the problem and list the current font path. For more information about
+setting the font path, see the -fontpath option description in the man
+page.
+</para>
+</sect3>
+
+<sect3>
+<title>Performance</title>
+
+<para>Phase I of development was not intended to optimize performance. Its
+focus was on completely and correctly handling the base X11 protocol in
+the Xdmx server. However, several insights were gained during Phase I,
+which are listed here for reference during the next phase of
+development.
+</para>
+
+<orderedlist>
+ <listitem>
+ <para>Calls to XSync() can slow down rendering since it requires a
+ complete round trip to and from a back-end server. This is
+ especially problematic when communicating over long haul networks.
+ </para></listitem>
+
+ <listitem>
+ <para>Sending drawing requests to only the screens that they overlap
+ should improve performance.
+ </para></listitem>
+</orderedlist>
+</sect3>
+
+<sect3>
+<title>Pixmaps</title>
+
+<para>Pixmaps were originally expected to be handled entirely in the
+front-end X server; however, it was found that this overly complicated
+the rendering code and would have required sending potentially large
+images to each back server that required them when copying from pixmap
+to screen. Thus, pixmap state is mirrored in the back-end server just
+as it is with regular window state. With this implementation, the same
+rendering code that draws to windows can be used to draw to pixmaps on
+the back-end server, and no large image transfers are required to copy
+from pixmap to window.
+</para>
+
+</sect3>
+
+</sect2>
+
+<!-- ============================================================ -->
+<sect2>
+<title>Phase II</title>
+
+<para>The second phase of development concentrates on performance
+optimizations. These optimizations are documented here, with
+<command>x11perf</command> data to show how the optimizations improve performance.
+</para>
+
+<para>All benchmarks were performed by running Xdmx on a dual processor
+1.4GHz AMD Athlon machine with 1GB of RAM connecting over 100baseT to
+two single-processor 1GHz Pentium III machines with 256MB of RAM and ATI
+Rage 128 (RF) video cards. The front end was running Linux
+2.4.20-pre1-ac1 and the back ends were running Linux 2.4.7-10 and
+version 4.2.99.1 of XFree86 pulled from the XFree86 CVS repository on
+August 7, 2002. All systems were running Red Hat Linux 7.2.
+</para>
+
+<sect3>
+<title>Moving from XFree86 4.1.99.1 to 4.2.0.0</title>
+
+<para>For phase II, the working source tree was moved to the branch tagged
+with dmx-1-0-branch and was updated from version 4.1.99.1 (20 August
+2001) of the XFree86 sources to version 4.2.0.0 (18 January 2002).
+After this update, the following tests were noted to be more than 10%
+faster:
+<screen>
+1.13 Fill 300x300 opaque stippled trapezoid (161x145 stipple)
+1.16 Fill 1x1 tiled trapezoid (161x145 tile)
+1.13 Fill 10x10 tiled trapezoid (161x145 tile)
+1.17 Fill 100x100 tiled trapezoid (161x145 tile)
+1.16 Fill 1x1 tiled trapezoid (216x208 tile)
+1.20 Fill 10x10 tiled trapezoid (216x208 tile)
+1.15 Fill 100x100 tiled trapezoid (216x208 tile)
+1.37 Circulate Unmapped window (200 kids)
+</screen>
+And the following tests were noted to be more than 10% slower:
+<screen>
+0.88 Unmap window via parent (25 kids)
+0.75 Circulate Unmapped window (4 kids)
+0.79 Circulate Unmapped window (16 kids)
+0.80 Circulate Unmapped window (25 kids)
+0.82 Circulate Unmapped window (50 kids)
+0.85 Circulate Unmapped window (75 kids)
+</screen>
+</para>
+
+<para>These changes were not caused by any changes in the DMX system, and
+may point to changes in the XFree86 tree or to tests that have more
+"jitter" than most other <command>x11perf</command> tests.
+</para>
+</sect3>
+
+<sect3>
+<title>Global changes</title>
+
+<para>During the development of the Phase II DMX server, several global
+changes were made. These changes were also compared with the Phase I
+server. The following tests were noted to be more than 10% faster:
+<screen>
+1.13 Fill 300x300 opaque stippled trapezoid (161x145 stipple)
+1.15 Fill 1x1 tiled trapezoid (161x145 tile)
+1.13 Fill 10x10 tiled trapezoid (161x145 tile)
+1.17 Fill 100x100 tiled trapezoid (161x145 tile)
+1.16 Fill 1x1 tiled trapezoid (216x208 tile)
+1.19 Fill 10x10 tiled trapezoid (216x208 tile)
+1.15 Fill 100x100 tiled trapezoid (216x208 tile)
+1.15 Circulate Unmapped window (4 kids)
+</screen>
+</para>
+
+<para>The following tests were noted to be more than 10% slower:
+<screen>
+0.69 Scroll 10x10 pixels
+0.68 Scroll 100x100 pixels
+0.68 Copy 10x10 from window to window
+0.68 Copy 100x100 from window to window
+0.76 Circulate Unmapped window (75 kids)
+0.83 Circulate Unmapped window (100 kids)
+</screen>
+</para>
+
+<para>For the remainder of this analysis, the baseline of comparison will
+be the Phase II deliverable with all optimizations disabled (unless
+otherwise noted). This will highlight how the optimizations in
+isolation impact performance.
+</para>
+</sect3>
+
+<sect3>
+<title>XSync() Batching</title>
+
+<para>During the Phase I implementation, XSync() was called after every
+protocol request made by the DMX server. This provided the DMX server
+with an interactive feel, but defeated X11's protocol buffering system
+and introduced round-trip wire latency into every operation. During
+Phase II, DMX was changed so that protocol requests are no longer
+followed by calls to XSync(). Instead, the need for an XSync() is
+noted, and XSync() calls are only made every 100mS or when the DMX
+server specifically needs to make a call to guarantee interactivity.
+With this new system, X11 buffers protocol as much as possible during a
+100mS interval, and many unnecessary XSync() calls are avoided.
+</para>
+
+<para>Out of more than 300 <command>x11perf</command> tests, 8 tests became more than 100
+times faster, with 68 more than 50X faster, 114 more than 10X faster,
+and 181 more than 2X faster. See table below for summary.
+</para>
+
+<para>The following tests were noted to be more than 10% slower with
+XSync() batching on:
+<screen>
+0.88 500x500 tiled rectangle (161x145 tile)
+0.89 Copy 500x500 from window to window
+</screen>
+</para>
+</sect3>
+
+<sect3>
+<title>Offscreen Optimization</title>
+
+<para>Windows span one or more of the back-end servers' screens; however,
+during Phase I development, windows were created on every back-end
+server and every rendering request was sent to every window regardless
+of whether or not that window was visible. With the offscreen
+optimization, the DMX server tracks when a window is completely off of a
+back-end server's screen and, in that case, it does not send rendering
+requests to those back-end windows. This optimization saves bandwidth
+between the front and back-end servers, and it reduces the number of
+XSync() calls. The performance tests were run on a DMX system with only
+two back-end servers. Greater performance gains will be had as the
+number of back-end servers increases.
+</para>
+
+<para>Out of more than 300 <command>x11perf</command> tests, 3 tests were at least twice as
+fast, and 146 tests were at least 10% faster. Two tests were more than
+10% slower with the offscreen optimization:
+<screen>
+0.88 Hide/expose window via popup (4 kids)
+0.89 Resize unmapped window (75 kids)
+</screen>
+</para>
+</sect3>
+
+<sect3>
+<title>Lazy Window Creation Optimization</title>
+
+<para>As mentioned above, during Phase I, windows were created on every
+back-end server even if they were not visible on that back-end. With
+the lazy window creation optimization, the DMX server does not create
+windows on a back-end server until they are either visible or they
+become the parents of a visible window. This optimization builds on the
+offscreen optimization (described above) and requires it to be enabled.
+</para>
+
+<para>The lazy window creation optimization works by creating the window
+data structures in the front-end server when a client creates a window,
+but delays creation of the window on the back-end server(s). A private
+window structure in the DMX server saves the relevant window data and
+tracks changes to the window's attributes and stacking order for later
+use. The only times a window is created on a back-end server are (1)
+when it is mapped and is at least partially overlapping the back-end
+server's screen (tracked by the offscreen optimization), or (2) when the
+window becomes the parent of a previously visible window. The first
+case occurs when a window is mapped or when a visible window is copied,
+moved or resized and now overlaps the back-end server's screen. The
+second case occurs when starting a window manager after having created
+windows to which the window manager needs to add decorations.
+</para>
+
+<para>When either case occurs, a window on the back-end server is created
+using the data saved in the DMX server's window private data structure.
+The stacking order is then adjusted to correctly place the window on the
+back-end and lastly the window is mapped. From this time forward, the
+window is handled exactly as if the window had been created at the time
+of the client's request.
+</para>
+
+<para>Note that when a window is no longer visible on a back-end server's
+screen (e.g., it is moved offscreen), the window is not destroyed;
+rather, it is kept and reused later if the window once again becomes
+visible on the back-end server's screen. Originally with this
+optimization, destroying windows was implemented but was later rejected
+because it increased bandwidth when windows were opaquely moved or
+resized, which is common in many window managers.
+</para>
+
+<para>The performance tests were run on a DMX system with only two back-end
+servers. Greater performance gains will be had as the number of
+back-end servers increases.
+</para>
+
+<para>This optimization improved the following <command>x11perf</command> tests by more
+than 10%:
+<screen>
+1.10 500x500 rectangle outline
+1.12 Fill 100x100 stippled trapezoid (161x145 stipple)
+1.20 Circulate Unmapped window (50 kids)
+1.19 Circulate Unmapped window (75 kids)
+</screen>
+</para>
+</sect3>
+
+<sect3>
+<title>Subdividing Rendering Primitives</title>
+
+<para>X11 imaging requests transfer significant data between the client and
+the X server. During Phase I, the DMX server would then transfer the
+image data to each back-end server. Even with the offscreen
+optimization (above), these requests still required transferring
+significant data to each back-end server that contained a visible
+portion of the window. For example, if the client uses XPutImage() to
+copy an image to a window that overlaps the entire DMX screen, then the
+entire image is copied by the DMX server to every back-end server.
+</para>
+
+<para>To reduce the amount of data transferred between the DMX server and
+the back-end servers when XPutImage() is called, the image data is
+subdivided and only the data that will be visible on a back-end server's
+screen is sent to that back-end server. Xinerama already implements a
+subdivision algorithm for XGetImage() and no further optimization was
+needed.
+</para>
+
+<para>Other rendering primitives were analyzed, but the time required to
+subdivide these primitives was a significant proportion of the time
+required to send the entire rendering request to the back-end server, so
+this optimization was rejected for the other rendering primitives.
+</para>
+
+<para>Again, the performance tests were run on a DMX system with only two
+back-end servers. Greater performance gains will be had as the number
+of back-end servers increases.
+</para>
+
+<para>This optimization improved the following <command>x11perf</command> tests by more
+than 10%:
+<screen>
+1.12 Fill 100x100 stippled trapezoid (161x145 stipple)
+1.26 PutImage 10x10 square
+1.83 PutImage 100x100 square
+1.91 PutImage 500x500 square
+1.40 PutImage XY 10x10 square
+1.48 PutImage XY 100x100 square
+1.50 PutImage XY 500x500 square
+1.45 Circulate Unmapped window (75 kids)
+1.74 Circulate Unmapped window (100 kids)
+</screen>
+</para>
+
+<para>The following test was noted to be more than 10% slower with this
+optimization:
+<screen>
+0.88 10-pixel fill chord partial circle
+</screen>
+</para>
+</sect3>
+
+<sect3>
+<title>Summary of x11perf Data</title>
+
+<para>With all of the optimizations on, 53 <command>x11perf</command> tests are more than
+100X faster than the unoptimized Phase II deliverable, with 69 more than
+50X faster, 73 more than 10X faster, and 199 more than twice as fast.
+No tests were more than 10% slower than the unoptimized Phase II
+deliverable. (Compared with the Phase I deliverable, only Circulate
+Unmapped window (100 kids) was more than 10% slower than the Phase II
+deliverable. As noted above, this test seems to have wider variability
+than other <command>x11perf</command> tests.)
+</para>
+
+<para>The following table summarizes relative <command>x11perf</command> test changes for
+all optimizations individually and collectively. Note that some of the
+optimizations have a synergistic effect when used together.
+<screen>
+
+1: XSync() batching only
+2: Off screen optimizations only
+3: Window optimizations only
+4: Subdivprims only
+5: All optimizations
+
+ 1 2 3 4 5 Operation
+------ ---- ---- ---- ------ ---------
+ 2.14 1.85 1.00 1.00 4.13 Dot
+ 1.67 1.80 1.00 1.00 3.31 1x1 rectangle
+ 2.38 1.43 1.00 1.00 2.44 10x10 rectangle
+ 1.00 1.00 0.92 0.98 1.00 100x100 rectangle
+ 1.00 1.00 1.00 1.00 1.00 500x500 rectangle
+ 1.83 1.85 1.05 1.06 3.54 1x1 stippled rectangle (8x8 stipple)
+ 2.43 1.43 1.00 1.00 2.41 10x10 stippled rectangle (8x8 stipple)
+ 0.98 1.00 1.00 1.00 1.00 100x100 stippled rectangle (8x8 stipple)
+ 1.00 1.00 1.00 1.00 0.98 500x500 stippled rectangle (8x8 stipple)
+ 1.75 1.75 1.00 1.00 3.40 1x1 opaque stippled rectangle (8x8 stipple)
+ 2.38 1.42 1.00 1.00 2.34 10x10 opaque stippled rectangle (8x8 stipple)
+ 1.00 1.00 0.97 0.97 1.00 100x100 opaque stippled rectangle (8x8 stipple)
+ 1.00 1.00 1.00 1.00 0.99 500x500 opaque stippled rectangle (8x8 stipple)
+ 1.82 1.82 1.04 1.04 3.56 1x1 tiled rectangle (4x4 tile)
+ 2.33 1.42 1.00 1.00 2.37 10x10 tiled rectangle (4x4 tile)
+ 1.00 0.92 1.00 1.00 1.00 100x100 tiled rectangle (4x4 tile)
+ 1.00 1.00 1.00 1.00 1.00 500x500 tiled rectangle (4x4 tile)
+ 1.94 1.62 1.00 1.00 3.66 1x1 stippled rectangle (17x15 stipple)
+ 1.74 1.28 1.00 1.00 1.73 10x10 stippled rectangle (17x15 stipple)
+ 1.00 1.00 1.00 0.89 0.98 100x100 stippled rectangle (17x15 stipple)
+ 1.00 1.00 1.00 1.00 0.98 500x500 stippled rectangle (17x15 stipple)
+ 1.94 1.62 1.00 1.00 3.67 1x1 opaque stippled rectangle (17x15 stipple)
+ 1.69 1.26 1.00 1.00 1.66 10x10 opaque stippled rectangle (17x15 stipple)
+ 1.00 0.95 1.00 1.00 1.00 100x100 opaque stippled rectangle (17x15 stipple)
+ 1.00 1.00 1.00 1.00 0.97 500x500 opaque stippled rectangle (17x15 stipple)
+ 1.93 1.61 0.99 0.99 3.69 1x1 tiled rectangle (17x15 tile)
+ 1.73 1.27 1.00 1.00 1.72 10x10 tiled rectangle (17x15 tile)
+ 1.00 1.00 1.00 1.00 0.98 100x100 tiled rectangle (17x15 tile)
+ 1.00 1.00 0.97 0.97 1.00 500x500 tiled rectangle (17x15 tile)
+ 1.95 1.63 1.00 1.00 3.83 1x1 stippled rectangle (161x145 stipple)
+ 1.80 1.30 1.00 1.00 1.83 10x10 stippled rectangle (161x145 stipple)
+ 0.97 1.00 1.00 1.00 1.01 100x100 stippled rectangle (161x145 stipple)
+ 1.00 1.00 1.00 1.00 0.98 500x500 stippled rectangle (161x145 stipple)
+ 1.95 1.63 1.00 1.00 3.56 1x1 opaque stippled rectangle (161x145 stipple)
+ 1.65 1.25 1.00 1.00 1.68 10x10 opaque stippled rectangle (161x145 stipple)
+ 1.00 1.00 1.00 1.00 1.01 100x100 opaque stippled rectangle (161x145...
+ 1.00 1.00 1.00 1.00 0.97 500x500 opaque stippled rectangle (161x145...
+ 1.95 1.63 0.98 0.99 3.80 1x1 tiled rectangle (161x145 tile)
+ 1.67 1.26 1.00 1.00 1.67 10x10 tiled rectangle (161x145 tile)
+ 1.13 1.14 1.14 1.14 1.14 100x100 tiled rectangle (161x145 tile)
+ 0.88 1.00 1.00 1.00 0.99 500x500 tiled rectangle (161x145 tile)
+ 1.93 1.63 1.00 1.00 3.53 1x1 tiled rectangle (216x208 tile)
+ 1.69 1.26 1.00 1.00 1.66 10x10 tiled rectangle (216x208 tile)
+ 1.00 1.00 1.00 1.00 1.00 100x100 tiled rectangle (216x208 tile)
+ 1.00 1.00 1.00 1.00 1.00 500x500 tiled rectangle (216x208 tile)
+ 1.82 1.70 1.00 1.00 3.38 1-pixel line segment
+ 2.07 1.56 0.90 1.00 3.31 10-pixel line segment
+ 1.29 1.10 1.00 1.00 1.27 100-pixel line segment
+ 1.05 1.06 1.03 1.03 1.09 500-pixel line segment
+ 1.30 1.13 1.00 1.00 1.29 100-pixel line segment (1 kid)
+ 1.32 1.15 1.00 1.00 1.32 100-pixel line segment (2 kids)
+ 1.33 1.16 1.00 1.00 1.33 100-pixel line segment (3 kids)
+ 1.92 1.64 1.00 1.00 3.73 10-pixel dashed segment
+ 1.34 1.16 1.00 1.00 1.34 100-pixel dashed segment
+ 1.24 1.11 0.99 0.97 1.23 100-pixel double-dashed segment
+ 1.72 1.77 1.00 1.00 3.25 10-pixel horizontal line segment
+ 1.83 1.66 1.01 1.00 3.54 100-pixel horizontal line segment
+ 1.86 1.30 1.00 1.00 1.84 500-pixel horizontal line segment
+ 2.11 1.52 1.00 0.99 3.02 10-pixel vertical line segment
+ 1.21 1.10 1.00 1.00 1.20 100-pixel vertical line segment
+ 1.03 1.03 1.00 1.00 1.02 500-pixel vertical line segment
+ 4.42 1.68 1.00 1.01 4.64 10x1 wide horizontal line segment
+ 1.83 1.31 1.00 1.00 1.83 100x10 wide horizontal line segment
+ 1.07 1.00 0.96 1.00 1.07 500x50 wide horizontal line segment
+ 4.10 1.67 1.00 1.00 4.62 10x1 wide vertical line segment
+ 1.50 1.24 1.06 1.06 1.48 100x10 wide vertical line segment
+ 1.06 1.03 1.00 1.00 1.05 500x50 wide vertical line segment
+ 2.54 1.61 1.00 1.00 3.61 1-pixel line
+ 2.71 1.48 1.00 1.00 2.67 10-pixel line
+ 1.19 1.09 1.00 1.00 1.19 100-pixel line
+ 1.04 1.02 1.00 1.00 1.03 500-pixel line
+ 2.68 1.51 0.98 1.00 3.17 10-pixel dashed line
+ 1.23 1.11 0.99 0.99 1.23 100-pixel dashed line
+ 1.15 1.08 1.00 1.00 1.15 100-pixel double-dashed line
+ 2.27 1.39 1.00 1.00 2.23 10x1 wide line
+ 1.20 1.09 1.00 1.00 1.20 100x10 wide line
+ 1.04 1.02 1.00 1.00 1.04 500x50 wide line
+ 1.52 1.45 1.00 1.00 1.52 100x10 wide dashed line
+ 1.54 1.47 1.00 1.00 1.54 100x10 wide double-dashed line
+ 1.97 1.30 0.96 0.95 1.95 10x10 rectangle outline
+ 1.44 1.27 1.00 1.00 1.43 100x100 rectangle outline
+ 3.22 2.16 1.10 1.09 3.61 500x500 rectangle outline
+ 1.95 1.34 1.00 1.00 1.90 10x10 wide rectangle outline
+ 1.14 1.14 1.00 1.00 1.13 100x100 wide rectangle outline
+ 1.00 1.00 1.00 1.00 1.00 500x500 wide rectangle outline
+ 1.57 1.72 1.00 1.00 3.03 1-pixel circle
+ 1.96 1.35 1.00 1.00 1.92 10-pixel circle
+ 1.21 1.07 0.86 0.97 1.20 100-pixel circle
+ 1.08 1.04 1.00 1.00 1.08 500-pixel circle
+ 1.39 1.19 1.03 1.03 1.38 100-pixel dashed circle
+ 1.21 1.11 1.00 1.00 1.23 100-pixel double-dashed circle
+ 1.59 1.28 1.00 1.00 1.58 10-pixel wide circle
+ 1.22 1.12 0.99 1.00 1.22 100-pixel wide circle
+ 1.06 1.04 1.00 1.00 1.05 500-pixel wide circle
+ 1.87 1.84 1.00 1.00 1.85 100-pixel wide dashed circle
+ 1.90 1.93 1.01 1.01 1.90 100-pixel wide double-dashed circle
+ 2.13 1.43 1.00 1.00 2.32 10-pixel partial circle
+ 1.42 1.18 1.00 1.00 1.42 100-pixel partial circle
+ 1.92 1.85 1.01 1.01 1.89 10-pixel wide partial circle
+ 1.73 1.67 1.00 1.00 1.73 100-pixel wide partial circle
+ 1.36 1.95 1.00 1.00 2.64 1-pixel solid circle
+ 2.02 1.37 1.00 1.00 2.03 10-pixel solid circle
+ 1.19 1.09 1.00 1.00 1.19 100-pixel solid circle
+ 1.02 0.99 1.00 1.00 1.01 500-pixel solid circle
+ 1.74 1.28 1.00 0.88 1.73 10-pixel fill chord partial circle
+ 1.31 1.13 1.00 1.00 1.31 100-pixel fill chord partial circle
+ 1.67 1.31 1.03 1.03 1.72 10-pixel fill slice partial circle
+ 1.30 1.13 1.00 1.00 1.28 100-pixel fill slice partial circle
+ 2.45 1.49 1.01 1.00 2.71 10-pixel ellipse
+ 1.22 1.10 1.00 1.00 1.22 100-pixel ellipse
+ 1.09 1.04 1.00 1.00 1.09 500-pixel ellipse
+ 1.90 1.28 1.00 1.00 1.89 100-pixel dashed ellipse
+ 1.62 1.24 0.96 0.97 1.61 100-pixel double-dashed ellipse
+ 2.43 1.50 1.00 1.00 2.42 10-pixel wide ellipse
+ 1.61 1.28 1.03 1.03 1.60 100-pixel wide ellipse
+ 1.08 1.05 1.00 1.00 1.08 500-pixel wide ellipse
+ 1.93 1.88 1.00 1.00 1.88 100-pixel wide dashed ellipse
+ 1.94 1.89 1.01 1.00 1.94 100-pixel wide double-dashed ellipse
+ 2.31 1.48 1.00 1.00 2.67 10-pixel partial ellipse
+ 1.38 1.17 1.00 1.00 1.38 100-pixel partial ellipse
+ 2.00 1.85 0.98 0.97 1.98 10-pixel wide partial ellipse
+ 1.89 1.86 1.00 1.00 1.89 100-pixel wide partial ellipse
+ 3.49 1.60 1.00 1.00 3.65 10-pixel filled ellipse
+ 1.67 1.26 1.00 1.00 1.67 100-pixel filled ellipse
+ 1.06 1.04 1.00 1.00 1.06 500-pixel filled ellipse
+ 2.38 1.43 1.01 1.00 2.32 10-pixel fill chord partial ellipse
+ 2.06 1.30 1.00 1.00 2.05 100-pixel fill chord partial ellipse
+ 2.27 1.41 1.00 1.00 2.27 10-pixel fill slice partial ellipse
+ 1.98 1.33 1.00 0.97 1.97 100-pixel fill slice partial ellipse
+ 57.46 1.99 1.01 1.00 114.92 Fill 1x1 equivalent triangle
+ 56.94 1.98 1.01 1.00 73.89 Fill 10x10 equivalent triangle
+ 6.07 1.75 1.00 1.00 6.07 Fill 100x100 equivalent triangle
+ 51.12 1.98 1.00 1.00 102.81 Fill 1x1 trapezoid
+ 51.42 1.82 1.01 1.00 94.89 Fill 10x10 trapezoid
+ 6.47 1.80 1.00 1.00 6.44 Fill 100x100 trapezoid
+ 1.56 1.28 1.00 0.99 1.56 Fill 300x300 trapezoid
+ 51.27 1.97 0.96 0.97 102.54 Fill 1x1 stippled trapezoid (8x8 stipple)
+ 51.73 2.00 1.02 1.02 67.92 Fill 10x10 stippled trapezoid (8x8 stipple)
+ 5.36 1.72 1.00 1.00 5.36 Fill 100x100 stippled trapezoid (8x8 stipple)
+ 1.54 1.26 1.00 1.00 1.59 Fill 300x300 stippled trapezoid (8x8 stipple)
+ 51.41 1.94 1.01 1.00 102.82 Fill 1x1 opaque stippled trapezoid (8x8 stipple)
+ 50.71 1.95 0.99 1.00 65.44 Fill 10x10 opaque stippled trapezoid (8x8...
+ 5.33 1.73 1.00 1.00 5.36 Fill 100x100 opaque stippled trapezoid (8x8...
+ 1.58 1.25 1.00 1.00 1.58 Fill 300x300 opaque stippled trapezoid (8x8...
+ 51.56 1.96 0.99 0.90 103.68 Fill 1x1 tiled trapezoid (4x4 tile)
+ 51.59 1.99 1.01 1.01 62.25 Fill 10x10 tiled trapezoid (4x4 tile)
+ 5.38 1.72 1.00 1.00 5.38 Fill 100x100 tiled trapezoid (4x4 tile)
+ 1.54 1.25 1.00 0.99 1.58 Fill 300x300 tiled trapezoid (4x4 tile)
+ 51.70 1.98 1.01 1.01 103.98 Fill 1x1 stippled trapezoid (17x15 stipple)
+ 44.86 1.97 1.00 1.00 44.86 Fill 10x10 stippled trapezoid (17x15 stipple)
+ 2.74 1.56 1.00 1.00 2.73 Fill 100x100 stippled trapezoid (17x15 stipple)
+ 1.29 1.14 1.00 1.00 1.27 Fill 300x300 stippled trapezoid (17x15 stipple)
+ 51.41 1.96 0.96 0.95 103.39 Fill 1x1 opaque stippled trapezoid (17x15...
+ 45.14 1.96 1.01 1.00 45.14 Fill 10x10 opaque stippled trapezoid (17x15...
+ 2.68 1.56 1.00 1.00 2.68 Fill 100x100 opaque stippled trapezoid (17x15...
+ 1.26 1.10 1.00 1.00 1.28 Fill 300x300 opaque stippled trapezoid (17x15...
+ 51.13 1.97 1.00 0.99 103.39 Fill 1x1 tiled trapezoid (17x15 tile)
+ 47.58 1.96 1.00 1.00 47.86 Fill 10x10 tiled trapezoid (17x15 tile)
+ 2.74 1.56 1.00 1.00 2.74 Fill 100x100 tiled trapezoid (17x15 tile)
+ 1.29 1.14 1.00 1.00 1.28 Fill 300x300 tiled trapezoid (17x15 tile)
+ 51.13 1.97 0.99 0.97 103.39 Fill 1x1 stippled trapezoid (161x145 stipple)
+ 45.14 1.97 1.00 1.00 44.29 Fill 10x10 stippled trapezoid (161x145 stipple)
+ 3.02 1.77 1.12 1.12 3.38 Fill 100x100 stippled trapezoid (161x145 stipple)
+ 1.31 1.13 1.00 1.00 1.30 Fill 300x300 stippled trapezoid (161x145 stipple)
+ 51.27 1.97 1.00 1.00 103.10 Fill 1x1 opaque stippled trapezoid (161x145...
+ 45.01 1.97 1.00 1.00 45.01 Fill 10x10 opaque stippled trapezoid (161x145...
+ 2.67 1.56 1.00 1.00 2.69 Fill 100x100 opaque stippled trapezoid (161x145..
+ 1.29 1.13 1.00 1.01 1.27 Fill 300x300 opaque stippled trapezoid (161x145..
+ 51.41 1.96 1.00 0.99 103.39 Fill 1x1 tiled trapezoid (161x145 tile)
+ 45.01 1.96 0.98 1.00 45.01 Fill 10x10 tiled trapezoid (161x145 tile)
+ 2.62 1.36 1.00 1.00 2.69 Fill 100x100 tiled trapezoid (161x145 tile)
+ 1.27 1.13 1.00 1.00 1.22 Fill 300x300 tiled trapezoid (161x145 tile)
+ 51.13 1.98 1.00 1.00 103.39 Fill 1x1 tiled trapezoid (216x208 tile)
+ 45.14 1.97 1.01 0.99 45.14 Fill 10x10 tiled trapezoid (216x208 tile)
+ 2.62 1.55 1.00 1.00 2.71 Fill 100x100 tiled trapezoid (216x208 tile)
+ 1.28 1.13 1.00 1.00 1.20 Fill 300x300 tiled trapezoid (216x208 tile)
+ 50.71 1.95 1.00 1.00 54.70 Fill 10x10 equivalent complex polygon
+ 5.51 1.71 0.96 0.98 5.47 Fill 100x100 equivalent complex polygons
+ 8.39 1.97 1.00 1.00 16.75 Fill 10x10 64-gon (Convex)
+ 8.38 1.83 1.00 1.00 8.43 Fill 100x100 64-gon (Convex)
+ 8.50 1.96 1.00 1.00 16.64 Fill 10x10 64-gon (Complex)
+ 8.26 1.83 1.00 1.00 8.35 Fill 100x100 64-gon (Complex)
+ 14.09 1.87 1.00 1.00 14.05 Char in 80-char line (6x13)
+ 11.91 1.87 1.00 1.00 11.95 Char in 70-char line (8x13)
+ 11.16 1.85 1.01 1.00 11.10 Char in 60-char line (9x15)
+ 10.09 1.78 1.00 1.00 10.09 Char16 in 40-char line (k14)
+ 6.15 1.75 1.00 1.00 6.31 Char16 in 23-char line (k24)
+ 11.92 1.90 1.03 1.03 11.88 Char in 80-char line (TR 10)
+ 8.18 1.78 1.00 0.99 8.17 Char in 30-char line (TR 24)
+ 42.83 1.44 1.01 1.00 42.11 Char in 20/40/20 line (6x13, TR 10)
+ 27.45 1.43 1.01 1.01 27.45 Char16 in 7/14/7 line (k14, k24)
+ 12.13 1.85 1.00 1.00 12.05 Char in 80-char image line (6x13)
+ 10.00 1.84 1.00 1.00 10.00 Char in 70-char image line (8x13)
+ 9.18 1.83 1.00 1.00 9.12 Char in 60-char image line (9x15)
+ 9.66 1.82 0.98 0.95 9.66 Char16 in 40-char image line (k14)
+ 5.82 1.72 1.00 1.00 5.99 Char16 in 23-char image line (k24)
+ 8.70 1.80 1.00 1.00 8.65 Char in 80-char image line (TR 10)
+ 4.67 1.66 1.00 1.00 4.67 Char in 30-char image line (TR 24)
+ 84.43 1.47 1.00 1.00 124.18 Scroll 10x10 pixels
+ 3.73 1.50 1.00 0.98 3.73 Scroll 100x100 pixels
+ 1.00 1.00 1.00 1.00 1.00 Scroll 500x500 pixels
+ 84.43 1.51 1.00 1.00 134.02 Copy 10x10 from window to window
+ 3.62 1.51 0.98 0.98 3.62 Copy 100x100 from window to window
+ 0.89 1.00 1.00 1.00 1.00 Copy 500x500 from window to window
+ 57.06 1.99 1.00 1.00 88.64 Copy 10x10 from pixmap to window
+ 2.49 2.00 1.00 1.00 2.48 Copy 100x100 from pixmap to window
+ 1.00 0.91 1.00 1.00 0.98 Copy 500x500 from pixmap to window
+ 2.04 1.01 1.00 1.00 2.03 Copy 10x10 from window to pixmap
+ 1.05 1.00 1.00 1.00 1.05 Copy 100x100 from window to pixmap
+ 1.00 1.00 0.93 1.00 1.04 Copy 500x500 from window to pixmap
+ 58.52 1.03 1.03 1.02 57.95 Copy 10x10 from pixmap to pixmap
+ 2.40 1.00 1.00 1.00 2.45 Copy 100x100 from pixmap to pixmap
+ 1.00 1.00 1.00 1.00 1.00 Copy 500x500 from pixmap to pixmap
+ 51.57 1.92 1.00 1.00 85.75 Copy 10x10 1-bit deep plane
+ 6.37 1.75 1.01 1.01 6.37 Copy 100x100 1-bit deep plane
+ 1.26 1.11 1.00 1.00 1.24 Copy 500x500 1-bit deep plane
+ 4.23 1.63 0.98 0.97 4.38 Copy 10x10 n-bit deep plane
+ 1.04 1.02 1.00 1.00 1.04 Copy 100x100 n-bit deep plane
+ 1.00 1.00 1.00 1.00 1.00 Copy 500x500 n-bit deep plane
+ 6.45 1.98 1.00 1.26 12.80 PutImage 10x10 square
+ 1.10 1.87 1.00 1.83 2.11 PutImage 100x100 square
+ 1.02 1.93 1.00 1.91 1.91 PutImage 500x500 square
+ 4.17 1.78 1.00 1.40 7.18 PutImage XY 10x10 square
+ 1.27 1.49 0.97 1.48 2.10 PutImage XY 100x100 square
+ 1.00 1.50 1.00 1.50 1.52 PutImage XY 500x500 square
+ 1.07 1.01 1.00 1.00 1.06 GetImage 10x10 square
+ 1.01 1.00 1.00 1.00 1.01 GetImage 100x100 square
+ 1.00 1.00 1.00 1.00 1.00 GetImage 500x500 square
+ 1.56 1.00 0.99 0.97 1.56 GetImage XY 10x10 square
+ 1.02 1.00 1.00 1.00 1.02 GetImage XY 100x100 square
+ 1.00 1.00 1.00 1.00 1.00 GetImage XY 500x500 square
+ 1.00 1.00 1.01 0.98 0.95 X protocol NoOperation
+ 1.02 1.03 1.04 1.03 1.00 QueryPointer
+ 1.03 1.02 1.04 1.03 1.00 GetProperty
+100.41 1.51 1.00 1.00 198.76 Change graphics context
+ 45.81 1.00 0.99 0.97 57.10 Create and map subwindows (4 kids)
+ 78.45 1.01 1.02 1.02 63.07 Create and map subwindows (16 kids)
+ 73.91 1.01 1.00 1.00 56.37 Create and map subwindows (25 kids)
+ 73.22 1.00 1.00 1.00 49.07 Create and map subwindows (50 kids)
+ 72.36 1.01 0.99 1.00 32.14 Create and map subwindows (75 kids)
+ 70.34 1.00 1.00 1.00 30.12 Create and map subwindows (100 kids)
+ 55.00 1.00 1.00 0.99 23.75 Create and map subwindows (200 kids)
+ 55.30 1.01 1.00 1.00 141.03 Create unmapped window (4 kids)
+ 55.38 1.01 1.01 1.00 163.25 Create unmapped window (16 kids)
+ 54.75 0.96 1.00 0.99 166.95 Create unmapped window (25 kids)
+ 54.83 1.00 1.00 0.99 178.81 Create unmapped window (50 kids)
+ 55.38 1.01 1.01 1.00 181.20 Create unmapped window (75 kids)
+ 55.38 1.01 1.01 1.00 181.20 Create unmapped window (100 kids)
+ 54.87 1.01 1.01 1.00 182.05 Create unmapped window (200 kids)
+ 28.13 1.00 1.00 1.00 30.75 Map window via parent (4 kids)
+ 36.14 1.01 1.01 1.01 32.58 Map window via parent (16 kids)
+ 26.13 1.00 0.98 0.95 29.85 Map window via parent (25 kids)
+ 40.07 1.00 1.01 1.00 27.57 Map window via parent (50 kids)
+ 23.26 0.99 1.00 1.00 18.23 Map window via parent (75 kids)
+ 22.91 0.99 1.00 0.99 16.52 Map window via parent (100 kids)
+ 27.79 1.00 1.00 0.99 12.50 Map window via parent (200 kids)
+ 22.35 1.00 1.00 1.00 56.19 Unmap window via parent (4 kids)
+ 9.57 1.00 0.99 1.00 89.78 Unmap window via parent (16 kids)
+ 80.77 1.01 1.00 1.00 103.85 Unmap window via parent (25 kids)
+ 96.34 1.00 1.00 1.00 116.06 Unmap window via parent (50 kids)
+ 99.72 1.00 1.00 1.00 124.93 Unmap window via parent (75 kids)
+112.36 1.00 1.00 1.00 125.27 Unmap window via parent (100 kids)
+105.41 1.00 1.00 0.99 120.00 Unmap window via parent (200 kids)
+ 51.29 1.03 1.02 1.02 74.19 Destroy window via parent (4 kids)
+ 86.75 0.99 0.99 0.99 116.87 Destroy window via parent (16 kids)
+106.43 1.01 1.01 1.01 127.49 Destroy window via parent (25 kids)
+120.34 1.01 1.01 1.00 140.11 Destroy window via parent (50 kids)
+126.67 1.00 0.99 0.99 145.00 Destroy window via parent (75 kids)
+126.11 1.01 1.01 1.00 140.56 Destroy window via parent (100 kids)
+128.57 1.01 1.00 1.00 137.91 Destroy window via parent (200 kids)
+ 16.04 0.88 1.00 1.00 20.36 Hide/expose window via popup (4 kids)
+ 19.04 1.01 1.00 1.00 23.48 Hide/expose window via popup (16 kids)
+ 19.22 1.00 1.00 1.00 20.44 Hide/expose window via popup (25 kids)
+ 17.41 1.00 0.91 0.97 17.68 Hide/expose window via popup (50 kids)
+ 17.29 1.01 1.00 1.01 17.07 Hide/expose window via popup (75 kids)
+ 16.74 1.00 1.00 1.00 16.17 Hide/expose window via popup (100 kids)
+ 10.30 1.00 1.00 1.00 10.51 Hide/expose window via popup (200 kids)
+ 16.48 1.01 1.00 1.00 26.05 Move window (4 kids)
+ 17.01 0.95 1.00 1.00 23.97 Move window (16 kids)
+ 16.95 1.00 1.00 1.00 22.90 Move window (25 kids)
+ 16.05 1.01 1.00 1.00 21.32 Move window (50 kids)
+ 15.58 1.00 0.98 0.98 19.44 Move window (75 kids)
+ 14.98 1.02 1.03 1.03 18.17 Move window (100 kids)
+ 10.90 1.01 1.01 1.00 12.68 Move window (200 kids)
+ 49.42 1.00 1.00 1.00 198.27 Moved unmapped window (4 kids)
+ 50.72 0.97 1.00 1.00 193.66 Moved unmapped window (16 kids)
+ 50.87 1.00 0.99 1.00 195.09 Moved unmapped window (25 kids)
+ 50.72 1.00 1.00 1.00 189.34 Moved unmapped window (50 kids)
+ 50.87 1.00 1.00 1.00 191.33 Moved unmapped window (75 kids)
+ 50.87 1.00 1.00 0.90 186.71 Moved unmapped window (100 kids)
+ 50.87 1.00 1.00 1.00 179.19 Moved unmapped window (200 kids)
+ 41.04 1.00 1.00 1.00 56.61 Move window via parent (4 kids)
+ 69.81 1.00 1.00 1.00 130.82 Move window via parent (16 kids)
+ 95.81 1.00 1.00 1.00 141.92 Move window via parent (25 kids)
+ 95.98 1.00 1.00 1.00 149.43 Move window via parent (50 kids)
+ 96.59 1.01 1.01 1.00 153.98 Move window via parent (75 kids)
+ 97.19 1.00 1.00 1.00 157.30 Move window via parent (100 kids)
+ 96.67 1.00 0.99 0.96 159.44 Move window via parent (200 kids)
+ 17.75 1.01 1.00 1.00 27.61 Resize window (4 kids)
+ 17.94 1.00 1.00 0.99 25.42 Resize window (16 kids)
+ 17.92 1.01 1.00 1.00 24.47 Resize window (25 kids)
+ 17.24 0.97 1.00 1.00 24.14 Resize window (50 kids)
+ 16.81 1.00 1.00 0.99 22.75 Resize window (75 kids)
+ 16.08 1.00 1.00 1.00 21.20 Resize window (100 kids)
+ 12.92 1.00 0.99 1.00 16.26 Resize window (200 kids)
+ 52.94 1.01 1.00 1.00 327.12 Resize unmapped window (4 kids)
+ 53.60 1.01 1.01 1.01 333.71 Resize unmapped window (16 kids)
+ 52.99 1.00 1.00 1.00 337.29 Resize unmapped window (25 kids)
+ 51.98 1.00 1.00 1.00 329.38 Resize unmapped window (50 kids)
+ 53.05 0.89 1.00 1.00 322.60 Resize unmapped window (75 kids)
+ 53.05 1.00 1.00 1.00 318.08 Resize unmapped window (100 kids)
+ 53.11 1.00 1.00 0.99 306.21 Resize unmapped window (200 kids)
+ 16.76 1.00 0.96 1.00 19.46 Circulate window (4 kids)
+ 17.24 1.00 1.00 0.97 16.24 Circulate window (16 kids)
+ 16.30 1.03 1.03 1.03 15.85 Circulate window (25 kids)
+ 13.45 1.00 1.00 1.00 14.90 Circulate window (50 kids)
+ 12.91 1.00 1.00 1.00 13.06 Circulate window (75 kids)
+ 11.30 0.98 1.00 1.00 11.03 Circulate window (100 kids)
+ 7.58 1.01 1.01 0.99 7.47 Circulate window (200 kids)
+ 1.01 1.01 0.98 1.00 0.95 Circulate Unmapped window (4 kids)
+ 1.07 1.07 1.01 1.07 1.02 Circulate Unmapped window (16 kids)
+ 1.04 1.09 1.06 1.05 0.97 Circulate Unmapped window (25 kids)
+ 1.04 1.23 1.20 1.18 1.05 Circulate Unmapped window (50 kids)
+ 1.18 1.53 1.19 1.45 1.24 Circulate Unmapped window (75 kids)
+ 1.08 1.02 1.01 1.74 1.01 Circulate Unmapped window (100 kids)
+ 1.01 1.12 0.98 0.91 0.97 Circulate Unmapped window (200 kids)
+</screen>
+</para>
+</sect3>
+
+<sect3>
+<title>Profiling with OProfile</title>
+
+<para>OProfile (available from http://oprofile.sourceforge.net/) is a
+system-wide profiler for Linux systems that uses processor-level
+counters to collect sampling data. OProfile can provide information
+that is similar to that provided by <command>gprof</command>, but without the
+necessity of recompiling the program with special instrumentation (i.e.,
+OProfile can collect statistical profiling information about optimized
+programs). A test harness was developed to collect OProfile data for
+each <command>x11perf</command> test individually.
+</para>
+
+<para>Test runs were performed using the RETIRED_INSNS counter on the AMD
+Athlon and the CPU_CLK_HALTED counter on the Intel Pentium III (with a
+test configuration different from the one described above). We have
+examined OProfile output and have compared it with <command>gprof</command> output.
+This investigation has not produced results that yield performance
+increases in <command>x11perf</command> numbers.
+</para>
+
+</sect3>
+
+<!--
+<sect3>Retired Instructions
+
+<p>The initial tests using OProfile were done using the RETIRED_INSNS
+counter with DMX running on the dual-processor AMD Athlon machine - the
+same test configuration that was described above and that was used for
+other tests. The RETIRED_INSNS counter counts retired instructions and
+showed drawing, text, copying, and image tests to be dominated (>
+30%) by calls to Hash(), SecurityLookupIDByClass(),
+SecurityLookupIDByType(), and StandardReadRequestFromClient(). Some of
+these tests also executed significant instructions in
+WaitForSomething().
+
+<p>In contrast, the window tests executed significant
+instructions in SecurityLookupIDByType(), Hash(),
+StandardReadRequestFromClient(), but also executed significant
+instructions in other routines, such as ConfigureWindow(). Some time
+was spent looking at Hash() function, but optimizations in this routine
+did not lead to a dramatic increase in <tt/x11perf/ performance.
+-->
+
+<!--
+<sect3>Clock Cycles
+
+<p>Retired instructions can be misleading because Intel/AMD instructions
+execute in variable amounts of time. The OProfile tests were repeated
+using the Intel CPU_CLK_HALTED counter with DMX running on the second
+back-end machine. Note that this is a different test configuration that
+the one described above. However, these tests show the amount of time
+(as measured in CPU cycles) that are spent in each routine. Because
+<tt/x11perf/ was running on the first back-end machine and because
+window optimizations were on, the load on the second back-end machine
+was not significant.
+
+<p>Using CPU_CLK_HALTED, DMX showed simple drawing
+tests spending more than 10% of their time in
+StandardReadRequestFromClient(), with significant time (> 20% total)
+spent in SecurityLookupIDByClass(), WaitForSomething(), and Dispatch().
+For these tests, < 5% of the time was spent in Hash(), which explains
+why optimizing the Hash() routine did not impact <tt/x11perf/ results.
+
+<p>The trapezoid, text, scrolling, copying, and image tests were
+dominated by time in ProcFillPoly(), PanoramiXFillPoly(), dmxFillPolygon(),
+SecurityLookupIDByClass(), SecurityLookupIDByType(), and
+StandardReadRequestFromClient(). Hash() time was generally above 5% but
+less than 10% of total time.
+-->
+
+<sect3>
+<title>X Test Suite</title>
+
+<para>The X Test Suite was run on the fully optimized DMX server using the
+configuration described above. The following failures were noted:
+<screen>
+XListPixmapFormats: Test 1 [1]
+XChangeWindowAttributes: Test 32 [1]
+XCreateWindow: Test 30 [1]
+XFreeColors: Test 4 [3]
+XCopyArea: Test 13, 17, 21, 25, 30 [2]
+XCopyPlane: Test 11, 15, 27, 31 [2]
+XSetFontPath: Test 4 [1]
+XChangeKeyboardControl: Test 9, 10 [1]
+
+[1] Previously documented errors expected from the Xinerama
+ implementation (see Phase I discussion).
+[2] Newly noted errors that have been verified as expected
+ behavior of the Xinerama implementation.
+[3] Newly noted error that has been verified as a Xinerama
+ implementation bug.
+</screen>
+</para>
+
+</sect3>
+
+</sect2>
+
+<!-- ============================================================ -->
+<sect2>
+<title>Phase III</title>
+
+<para>During the third phase of development, support was provided for the
+following extensions: SHAPE, RENDER, XKEYBOARD, XInput.
+</para>
+
+<sect3>
+<title>SHAPE</title>
+
+<para>The SHAPE extension is supported. Test applications (e.g., xeyes and
+oclock) and window managers that make use of the SHAPE extension will
+work as expected.
+</para>
+</sect3>
+
+<sect3>
+<title>RENDER</title>
+
+<para>The RENDER extension is supported. The version included in the DMX
+CVS tree is version 0.2, and this version is fully supported by Xdmx.
+Applications using only version 0.2 functions will work correctly;
+however, some apps that make use of functions from later versions do not
+properly check the extension's major/minor version numbers. These apps
+will fail with a Bad Implementation error when using post-version 0.2
+functions. This is expected behavior. When the DMX CVS tree is updated
+to include newer versions of RENDER, support for these newer functions
+will be added to the DMX X server.
+</para>
+</sect3>
+
+<sect3>
+<title>XKEYBOARD</title>
+
+<para>The XKEYBOARD extension is supported. If present on the back-end X
+servers, the XKEYBOARD extension will be used to obtain information
+about the type of the keyboard for initialization. Otherwise, the
+keyboard will be initialized using defaults. Note that this departs
+from older behavior: when Xdmx is compiled without XKEYBOARD support,
+the map from the back-end X server will be preserved. With XKEYBOARD
+support, the map is not preserved because better information and control
+of the keyboard is available.
+</para>
+</sect3>
+
+<sect3>
+<title>XInput</title>
+
+<para>The XInput extension is supported. Any device can be used as a core
+device and be used as an XInput extension device, with the exception of
+core devices on the back-end servers. This limitation is present
+because cursor handling on the back-end requires that the back-end
+cursor sometimes track the Xdmx core cursor -- behavior that is
+incompatible with using the back-end pointer as a non-core device.
+</para>
+
+<para>Currently, back-end extension devices are not available as Xdmx
+extension devices, but this limitation should be removed in the future.
+</para>
+
+<para>To demonstrate the XInput extension, and to provide more examples for
+low-level input device driver writers, USB device drivers have been
+written for mice (usb-mou), keyboards (usb-kbd), and
+non-mouse/non-keyboard USB devices (usb-oth). Please see the man page
+for information on Linux kernel drivers that are required for using
+these Xdmx drivers.
+</para>
+</sect3>
+
+<sect3>
+<title>DPMS</title>
+
+<para>The DPMS extension is exported but does not do anything at this time.
+</para>
+
+</sect3>
+
+<sect3>
+<title>Other Extensions</title>
+
+<para>The LBX,
+ SECURITY,
+ XC-APPGROUP, and
+ XFree86-Bigfont
+extensions do not require any special Xdmx support and have been exported.
+</para>
+
+<para>The
+ BIG-REQUESTS,
+ DEC-XTRAP,
+ DOUBLE-BUFFER,
+ Extended-Visual-Information,
+ FontCache,
+ GLX,
+ MIT-SCREEN-SAVER,
+ MIT-SHM,
+ MIT-SUNDRY-NONSTANDARD,
+ RECORD,
+ SECURITY,
+ SGI-GLX,
+ SYNC,
+ TOG-CUP,
+ X-Resource,
+ XC-MISC,
+ XFree86-DGA,
+ XFree86-DRI,
+ XFree86-Misc,
+ XFree86-VidModeExtension, and
+ XVideo
+extensions are <emphasis remap="it">not</emphasis> supported at this time, but will be evaluated
+for inclusion in future DMX releases. <emphasis remap="bf">See below for additional work
+on extensions after Phase III.</emphasis>
+</para>
+</sect3>
+</sect2>
+
+<sect2>
+<title>Phase IV</title>
+
+<sect3>
+<title>Moving to XFree86 4.3.0</title>
+
+<para>For Phase IV, the recent release of XFree86 4.3.0 (27 February 2003)
+was merged onto the dmx.sourceforge.net CVS trunk and all work is
+proceeding using this tree.
+</para>
+</sect3>
+
+<sect3>
+<title>Extensions </title>
+
+<sect4>
+<title>XC-MISC (supported)</title>
+
+<para>XC-MISC is used internally by the X library to recycle XIDs from the
+X server. This is important for long-running X server sessions. Xdmx
+supports this extension. The X Test Suite passed and failed the exact
+same tests before and after this extension was enabled.
+<!-- Tested February/March 2003 -->
+</para>
+</sect4>
+
+<sect4>
+<title>Extended-Visual-Information (supported)</title>
+
+<para>The Extended-Visual-Information extension provides a method for an X
+client to obtain detailed visual information. Xdmx supports this
+extension. It was tested using the <filename>hw/dmx/examples/evi</filename> example
+program. <emphasis remap="bf">Note that this extension is not Xinerama-aware</emphasis> -- it will
+return visual information for each screen even though Xinerama is
+causing the X server to export a single logical screen.
+<!-- Tested March 2003 -->
+</para>
+</sect4>
+
+<sect4>
+<title>RES (supported)</title>
+
+<para>The X-Resource extension provides a mechanism for a client to obtain
+detailed information about the resources used by other clients. This
+extension was tested with the <filename>hw/dmx/examples/res</filename> program. The
+X Test Suite passed and failed the exact same tests before and after
+this extension was enabled.
+<!-- Tested March 2003 -->
+</para>
+</sect4>
+
+<sect4>
+<title>BIG-REQUESTS (supported)</title>
+
+<para>This extension enables the X11 protocol to handle requests longer
+than 262140 bytes. The X Test Suite passed and failed the exact same
+tests before and after this extension was enabled.
+<!-- Tested March 2003 -->
+</para>
+</sect4>
+
+<sect4>
+<title>XSYNC (supported)</title>
+
+<para>This extension provides facilities for two different X clients to
+synchronize their requests. This extension was minimally tested with
+<command>xdpyinfo</command> and the X Test Suite passed and failed the exact same
+tests before and after this extension was enabled.
+<!-- Tested March 2003 -->
+</para>
+</sect4>
+
+<sect4>
+<title>XTEST, RECORD, DEC-XTRAP (supported) and XTestExtension1 (not supported)</title>
+
+<para>The XTEST and RECORD extension were developed by the X Consortium for
+use in the X Test Suite and are supported as a standard in the X11R6
+tree. They are also supported in Xdmx. When X Test Suite tests that
+make use of the XTEST extension are run, Xdmx passes and fails exactly
+the same tests as does a standard XFree86 X server. When the
+<literal remap="tt">rcrdtest</literal> test (a part of the X Test Suite that verifies the RECORD
+extension) is run, Xdmx passes and fails exactly the same tests as does
+a standard XFree86 X server. <!-- Tested February/March 2003 -->
+</para>
+
+<para>There are two older XTEST-like extensions: DEC-XTRAP and
+XTestExtension1. The XTestExtension1 extension was developed for use by
+the X Testing Consortium for use with a test suite that eventually
+became (part of?) the X Test Suite. Unlike XTEST, which only allows
+events to be sent to the server, the XTestExtension1 extension also
+allowed events to be recorded (similar to the RECORD extension). The
+second is the DEC-XTRAP extension that was developed by the Digital
+Equipment Corporation.
+</para>
+
+<para>The DEC-XTRAP extension is available from Xdmx and has been tested
+with the <command>xtrap*</command> tools which are distributed as standard X11R6
+clients. <!-- Tested March 2003 -->
+</para>
+
+<para>The XTestExtension1 is <emphasis>not</emphasis> supported because it does not appear
+to be used by any modern X clients (the few that support it also support
+XTEST) and because there are no good methods available for testing that
+it functions correctly (unlike XTEST and DEC-XTRAP, the code for
+XTestExtension1 is not part of the standard X server source tree, so
+additional testing is important). <!-- Tested March 2003 -->
+</para>
+
+<para>Most of these extensions are documented in the X11R6 source tree.
+Further, several original papers exist that this author was unable to
+locate -- for completeness and historical interest, citations are
+provide:
+<variablelist>
+<varlistentry>
+<term>XRECORD</term>
+<listitem>
+<para>Martha Zimet. Extending X For Recording. 8th Annual X
+Technical Conference Boston, MA January 24-26, 1994.
+</para></listitem></varlistentry>
+<varlistentry>
+<term>DEC-XTRAP</term>
+<listitem>
+<para>Dick Annicchiarico, Robert Chesler, Alan Jamison. XTrap
+Architecture. Digital Equipment Corporation, July 1991.
+</para></listitem></varlistentry>
+<varlistentry>
+<term>XTestExtension1</term>
+<listitem>
+<para>Larry Woestman. X11 Input Synthesis Extension
+Proposal. Hewlett Packard, November 1991.
+</para></listitem></varlistentry>
+</variablelist>
+</para>
+</sect4>
+
+<sect4>
+<title>MIT-MISC (not supported)</title>
+
+<para>The MIT-MISC extension is used to control a bug-compatibility flag
+that provides compatibility with xterm programs from X11R1 and X11R2.
+There does not appear to be a single client available that makes use of
+this extension and there is not way to verify that it works correctly.
+The Xdmx server does <emphasis>not</emphasis> support MIT-MISC.
+</para>
+</sect4>
+
+<sect4>
+<title>SCREENSAVER (not supported)</title>
+
+<para>This extension provides special support for the X screen saver. It
+was tested with beforelight, which appears to be the only client that
+works with it. When Xinerama was not active, <command>beforelight</command> behaved
+as expected. However, when Xinerama was active, <command>beforelight</command> did
+not behave as expected. Further, when this extension is not active,
+<command>xscreensaver</command> (a widely-used X screen saver program) did not behave
+as expected. Since this extension is not Xinerama-aware and is not
+commonly used with expected results by clients, we have left this
+extension disabled at this time.
+</para>
+</sect4>
+
+<sect4>
+<title>GLX (supported)</title>
+
+<para>The GLX extension provides OpenGL and GLX windowing support. In
+Xdmx, the extension is called glxProxy, and it is Xinerama aware. It
+works by either feeding requests forward through Xdmx to each of the
+back-end servers or handling them locally. All rendering requests are
+handled on the back-end X servers. This code was donated to the DMX
+project by SGI. For the X Test Suite results comparison, see below.
+</para>
+</sect4>
+
+<sect4>
+<title>RENDER (supported)</title>
+
+<para>The X Rendering Extension (RENDER) provides support for digital image
+composition. Geometric and text rendering are supported. RENDER is
+partially Xinerama-aware, with text and the most basic compositing
+operator; however, its higher level primitives (triangles, triangle
+strips, and triangle fans) are not yet Xinerama-aware. The RENDER
+extension is still under development, and is currently at version 0.8.
+Additional support will be required in DMX as more primitives and/or
+requests are added to the extension.
+</para>
+
+<para>There is currently no test suite for the X Rendering Extension;
+however, there has been discussion of developing a test suite as the
+extension matures. When that test suite becomes available, additional
+testing can be performed with Xdmx. The X Test Suite passed and failed
+the exact same tests before and after this extension was enabled.
+</para>
+</sect4>
+
+<sect4>
+<title>Summary</title>
+
+<!-- WARNING: this list is duplicated in the "Common X extension
+support" section -->
+<para>To summarize, the following extensions are currently supported:
+ BIG-REQUESTS,
+ DEC-XTRAP,
+ DMX,
+ DPMS,
+ Extended-Visual-Information,
+ GLX,
+ LBX,
+ RECORD,
+ RENDER,
+ SECURITY,
+ SHAPE,
+ SYNC,
+ X-Resource,
+ XC-APPGROUP,
+ XC-MISC,
+ XFree86-Bigfont,
+ XINERAMA,
+ XInputExtension,
+ XKEYBOARD, and
+ XTEST.
+</para>
+
+<para>The following extensions are <emphasis>not</emphasis> supported at this time:
+ DOUBLE-BUFFER,
+ FontCache,
+ MIT-SCREEN-SAVER,
+ MIT-SHM,
+ MIT-SUNDRY-NONSTANDARD,
+ TOG-CUP,
+ XFree86-DGA,
+ XFree86-Misc,
+ XFree86-VidModeExtension,
+ XTestExtensionExt1, and
+ XVideo.
+</para>
+</sect4>
+</sect3>
+
+<sect3>
+<title>Additional Testing with the X Test Suite</title>
+
+<sect4>
+<title>XFree86 without XTEST</title>
+
+<para>After the release of XFree86 4.3.0, we retested the XFree86 X server
+with and without using the XTEST extension. When the XTEST extension
+was <emphasis>not</emphasis> used for testing, the XFree86 4.3.0 server running on our
+usual test system with a Radeon VE card reported unexpected failures in
+the following tests:
+<literallayout>
+XListPixmapFormats: Test 1
+XChangeKeyboardControl: Tests 9, 10
+XGetDefault: Test 5
+XRebindKeysym: Test 1
+</literallayout>
+</para>
+</sect4>
+
+<sect4>
+<title>XFree86 with XTEST</title>
+
+<para>When using the XTEST extension, the XFree86 4.3.0 server reported the
+following errors:
+<literallayout>
+XListPixmapFormats: Test 1
+XChangeKeyboardControl: Tests 9, 10
+XGetDefault: Test 5
+XRebindKeysym: Test 1
+
+XAllowEvents: Tests 20, 21, 24
+XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
+XGrabKey: Test 8
+XSetPointerMapping: Test 3
+XUngrabButton: Test 4
+</literallayout>
+</para>
+
+<para>While these errors may be important, they will probably be fixed
+eventually in the XFree86 source tree. We are particularly interested
+in demonstrating that the Xdmx server does not introduce additional
+failures that are not known Xinerama failures.
+</para>
+</sect4>
+
+<sect4>
+<title>Xdmx with XTEST, without Xinerama, without GLX</title>
+
+<para>Without Xinerama, but using the XTEST extension, the following errors
+were reported from Xdmx (note that these are the same as for the XFree86
+4.3.0, except that XGetDefault no longer fails):
+<literallayout>
+XListPixmapFormats: Test 1
+XChangeKeyboardControl: Tests 9, 10
+XRebindKeysym: Test 1
+
+XAllowEvents: Tests 20, 21, 24
+XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
+XGrabKey: Test 8
+XSetPointerMapping: Test 3
+XUngrabButton: Test 4
+</literallayout>
+</para>
+</sect4>
+
+<sect4>
+<title>Xdmx with XTEST, with Xinerama, without GLX</title>
+
+<para>With Xinerama, using the XTEST extension, the following errors
+were reported from Xdmx:
+<literallayout>
+XListPixmapFormats: Test 1
+XChangeKeyboardControl: Tests 9, 10
+XRebindKeysym: Test 1
+
+XAllowEvents: Tests 20, 21, 24
+XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
+XGrabKey: Test 8
+XSetPointerMapping: Test 3
+XUngrabButton: Test 4
+
+XCopyPlane: Tests 13, 22, 31 (well-known XTEST/Xinerama interaction issue)
+XDrawLine: Test 67
+XDrawLines: Test 91
+XDrawSegments: Test 68
+</literallayout>
+Note that the first two sets of errors are the same as for the XFree86
+4.3.0 server, and that the XCopyPlane error is a well-known error
+resulting from an XTEST/Xinerama interaction when the request crosses a
+screen boundary. The XDraw* errors are resolved when the tests are run
+individually and they do not cross a screen boundary. We will
+investigate these errors further to determine their cause.
+</para>
+</sect4>
+
+<sect4>
+<title>Xdmx with XTEST, with Xinerama, with GLX</title>
+
+<para>With GLX enabled, using the XTEST extension, the following errors
+were reported from Xdmx (these results are from early during the Phase
+IV development, but were confirmed with a late Phase IV snapshot):
+<literallayout>
+XListPixmapFormats: Test 1
+XChangeKeyboardControl: Tests 9, 10
+XRebindKeysym: Test 1
+
+XAllowEvents: Tests 20, 21, 24
+XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
+XGrabKey: Test 8
+XSetPointerMapping: Test 3
+XUngrabButton: Test 4
+
+XClearArea: Test 8
+XCopyArea: Tests 4, 5, 11, 14, 17, 23, 25, 27, 30
+XCopyPlane: Tests 6, 7, 10, 19, 22, 31
+XDrawArcs: Tests 89, 100, 102
+XDrawLine: Test 67
+XDrawSegments: Test 68
+</literallayout>
+Note that the first two sets of errors are the same as for the XFree86
+4.3.0 server, and that the third set has different failures than when
+Xdmx does not include GLX support. Since the GLX extension adds new
+visuals to support GLX's visual configs and the X Test Suite runs tests
+over the entire set of visuals, additional rendering tests were run and
+presumably more of them crossed a screen boundary. This conclusion is
+supported by the fact that nearly all of the rendering errors reported
+are resolved when the tests are run individually and they do no cross a
+screen boundary.
+</para>
+
+<para>Further, when hardware rendering is disabled on the back-end displays,
+many of the errors in the third set are eliminated, leaving only:
+<literallayout>
+XClearArea: Test 8
+XCopyArea: Test 4, 5, 11, 14, 17, 23, 25, 27, 30
+XCopyPlane: Test 6, 7, 10, 19, 22, 31
+</literallayout>
+</para>
+</sect4>
+
+<sect4>
+<title>Conclusion</title>
+
+<para>We conclude that all of the X Test Suite errors reported for Xdmx are
+the result of errors in the back-end X server or the Xinerama
+implementation. Further, all of these errors that can be reasonably
+fixed at the Xdmx layer have been. (Where appropriate, we have
+submitted patches to the XFree86 and Xinerama upstream maintainers.)
+</para>
+</sect4>
+</sect3>
+
+<sect3>
+<title>Dynamic Reconfiguration</title>
+
+<para>During this development phase, dynamic reconfiguration support was
+added to DMX. This support allows an application to change the position
+and offset of a back-end server's screen. For example, if the
+application would like to shift a screen slightly to the left, it could
+query Xdmx for the screen's <x,y> position and then dynamically
+reconfigure that screen to be at position <x+10,y>. When a screen
+is dynamically reconfigured, input handling and a screen's root window
+dimensions are adjusted as needed. These adjustments are transparent to
+the user.
+</para>
+
+<sect4>
+<title>Dynamic reconfiguration extension</title>
+
+<para>The application interface to DMX's dynamic reconfiguration is through
+a function in the DMX extension library:
+<programlisting>
+Bool DMXReconfigureScreen(Display *dpy, int screen, int x, int y)
+</programlisting>
+where <parameter>dpy</parameter> is DMX server's display, <parameter>screen</parameter> is the number of the
+screen to be reconfigured, and <parameter>x</parameter> and <parameter>y</parameter> are the new upper,
+left-hand coordinates of the screen to be reconfigured.
+</para>
+
+<para>The coordinates are not limited other than as required by the X
+protocol, which limits all coordinates to a signed 16 bit number. In
+addition, all coordinates within a screen must also be legal values.
+Therefore, setting a screen's upper, left-hand coordinates such that the
+right or bottom edges of the screen is greater than 32,767 is illegal.
+</para>
+</sect4>
+
+<sect4>
+<title>Bounding box</title>
+
+<para>When the Xdmx server is started, a bounding box is calculated from
+the screens' layout given either on the command line or in the
+configuration file. This bounding box is currently fixed for the
+lifetime of the Xdmx server.
+</para>
+
+<para>While it is possible to move a screen outside of the bounding box, it
+is currently not possible to change the dimensions of the bounding box.
+For example, it is possible to specify coordinates of <-100,-100>
+for the upper, left-hand corner of the bounding box, which was
+previously at coordinates <0,0>. As expected, the screen is moved
+down and to the right; however, since the bounding box is fixed, the
+left side and upper portions of the screen exposed by the
+reconfiguration are no longer accessible on that screen. Those
+inaccessible regions are filled with black.
+</para>
+
+<para>This fixed bounding box limitation will be addressed in a future
+development phase.
+</para>
+</sect4>
+
+<sect4>
+<title>Sample applications</title>
+
+<para>An example of where this extension is useful is in setting up a video
+wall. It is not always possible to get everything perfectly aligned,
+and sometimes the positions are changed (e.g., someone might bump into a
+projector). Instead of physically moving projectors or monitors, it is
+now possible to adjust the positions of the back-end server's screens
+using the dynamic reconfiguration support in DMX.
+</para>
+
+<para>Other applications, such as automatic setup and calibration tools,
+can make use of dynamic reconfiguration to correct for projector
+alignment problems, as long as the projectors are still arranged
+rectilinearly. Horizontal and vertical keystone correction could be
+applied to projectors to correct for non-rectilinear alignment problems;
+however, this must be done external to Xdmx.
+</para>
+
+<para>A sample test program is included in the DMX server's examples
+directory to demonstrate the interface and how an application might use
+dynamic reconfiguration. See <filename>dmxreconfig.c</filename> for details.
+</para>
+</sect4>
+
+<sect4>
+<title>Additional notes</title>
+
+<para>In the original development plan, Phase IV was primarily devoted to
+adding OpenGL support to DMX; however, SGI became interested in the DMX
+project and developed code to support OpenGL/GLX. This code was later
+donated to the DMX project and integrated into the DMX code base, which
+freed the DMX developers to concentrate on dynamic reconfiguration (as
+described above).
+</para>
+</sect4>
+</sect3>
+
+<sect3>
+<title>Doxygen documentation</title>
+
+<para>Doxygen is an open-source (GPL) documentation system for generating
+browseable documentation from stylized comments in the source code. We
+have placed all of the Xdmx server and DMX protocol source code files
+under Doxygen so that comprehensive documentation for the Xdmx source
+code is available in an easily browseable format.
+</para>
+</sect3>
+
+<sect3>
+<title>Valgrind</title>
+
+<para>Valgrind, an open-source (GPL) memory debugger for Linux, was used to
+search for memory management errors. Several memory leaks were detected
+and repaired. The following errors were not addressed:
+<orderedlist>
+ <listitem><para>
+ When the X11 transport layer sends a reply to the client, only
+ those fields that are required by the protocol are filled in --
+ unused fields are left as uninitialized memory and are therefore
+ noted by valgrind. These instances are not errors and were not
+ repaired.
+ </para></listitem>
+ <listitem><para>
+ At each server generation, glxInitVisuals allocates memory that
+ is never freed. The amount of memory lost each generation
+ approximately equal to 128 bytes for each back-end visual.
+ Because the code involved is automatically generated, this bug
+ has not been fixed and will be referred to SGI.
+ </para></listitem>
+ <listitem><para>
+ At each server generation, dmxRealizeFont calls XLoadQueryFont,
+ which allocates a font structure that is not freed.
+ dmxUnrealizeFont can free the font structure for the first
+ screen, but cannot free it for the other screens since they are
+ already closed by the time dmxUnrealizeFont could free them.
+ The amount of memory lost each generation is approximately equal
+ to 80 bytes per font per back-end. When this bug is fixed in
+ the the X server's device-independent (dix) code, DMX will be
+ able to properly free the memory allocated by XLoadQueryFont.
+ </para></listitem>
+</orderedlist>
+</para>
+</sect3>
+
+<sect3>
+<title>RATS</title>
+
+<para>RATS (Rough Auditing Tool for Security) is an open-source (GPL)
+security analysis tool that scans source code for common
+security-related programming errors (e.g., buffer overflows and TOCTOU
+races). RATS was used to audit all of the code in the hw/dmx directory
+and all "High" notations were checked manually. The code was either
+re-written to eliminate the warning, or a comment containing "RATS" was
+inserted on the line to indicate that a human had checked the code.
+Unrepaired warnings are as follows:
+<orderedlist>
+ <listitem><para>
+ Fixed-size buffers are used in many areas, but code has been
+ added to protect against buffer overflows (e.g., XmuSnprint).
+ The only instances that have not yet been fixed are in
+ config/xdmxconfig.c (which is not part of the Xdmx server) and
+ input/usb-common.c.
+ </para></listitem>
+ <listitem><para>
+ vprintf and vfprintf are used in the logging routines. In
+ general, all uses of these functions (e.g., dmxLog) provide a
+ constant format string from a trusted source, so the use is
+ relatively benign.
+ </para></listitem>
+ <listitem><para>
+ glxProxy/glxscreens.c uses getenv and strcat. The use of these
+ functions is safe and will remain safe as long as
+ ExtensionsString is longer then GLXServerExtensions (ensuring
+ this may not be ovious to the casual programmer, but this is in
+ automatically generated code, so we hope that the generator
+ enforces this constraint).
+ </para></listitem>
+</orderedlist>
+
+</para>
+
+</sect3>
+
+</sect2>
+
+</sect1>
+
+</appendix>
+
+ </article>
+
+ <!-- Local Variables: -->
+ <!-- fill-column: 72 -->
+ <!-- End: -->
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