  Distributed Multihead X design
  Kevin E. Martin, David H. Dawes, and Rickard E. Faith

  29 June 2004 (created 25 July 2001)

  This document covers the motivation, background, design, and implemen-
  tation 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.
  Copyright 2001 by VA Linux Systems, Inc., Fremont, California.  Copy-
  right 2001-2004 by Red Hat, Inc., Raleigh, North Carolina

  ______________________________________________________________________

  Table of Contents



  1. Introduction
     1.1 The Distributed Multihead X Server
     1.2 Layout of Paper

  2. Development plan
     2.1 Bootstrap code
     2.2 Input device handling
     2.3 Output device handling
        2.3.1 Initialization
        2.3.2 Handling rendering requests
     2.4 Optimizing DMX
     2.5 DMX X extension support
     2.6 Common X extension support
     2.7 OpenGL support

  3. Current issues
     3.1 Fonts
     3.2 Zero width rendering primitives
     3.3 Output scaling
     3.4 Per-screen colormaps

  A. Background
     A.1 Core input device handling
        A.1.1 InitInput()
        A.1.2 InitAndStartDevices()
        A.1.3 devReadInput()
        A.1.4 ProcessInputEvents()
        A.1.5 DisableDevice()
        A.1.6 CloseDevice()
        A.1.7 LegalModifier()
     A.2 Output handling
        A.2.1 InitOutput()
        A.2.2 AddScreen()
        A.2.3 ScreenInit()
        A.2.4 CloseScreen()
        A.2.5 GC operations
        A.2.6 Xnest
        A.2.7 Shadow framebuffer
     A.3 Xinerama
        A.3.1 Xinerama-specific changes to the DIX code
        A.3.2 Xinerama-specific changes to the MI code
        A.3.3 Intercepted DIX core requests

  B. Development Results
     B.1 Phase I
        B.1.1 Scope
        B.1.2 Results
        B.1.3 X Test Suite
           B.1.3.1 Introduction
           B.1.3.2 Expected Failures for a Single Head
           B.1.3.3 Expected Failures for Xinerama
           B.1.3.4 Additional Failures from Xdmx
           B.1.3.5 Summary and Future Work
        B.1.4 Fonts
        B.1.5 Performance
        B.1.6 Pixmaps
     B.2 Phase II
        B.2.1 Moving from XFree86 4.1.99.1 to 4.2.0.0
        B.2.2 Global changes
        B.2.3 XSync() Batching
        B.2.4 Offscreen Optimization
        B.2.5 Lazy Window Creation Optimization
        B.2.6 Subdividing Rendering Primitives
        B.2.7 Summary of x11perf Data
        B.2.8 Profiling with OProfile
        B.2.9 X Test Suite
     B.3 Phase III
        B.3.1 SHAPE
        B.3.2 RENDER
        B.3.3 XKEYBOARD
        B.3.4 XInput
        B.3.5 DPMS
        B.3.6 Other Extensions
     B.4 Phase IV
        B.4.1 Moving to XFree86 4.3.0
        B.4.2 Extensions
           B.4.2.1 XC-MISC (supported)
           B.4.2.2 Extended-Visual-Information (supported)
           B.4.2.3 RES (supported)
           B.4.2.4 BIG-REQUESTS (supported)
           B.4.2.5 XSYNC (supported)
           B.4.2.6 XTEST, RECORD, DEC-XTRAP (supported) and XTestExtension1 (not supported)
           B.4.2.7 MIT-MISC (not supported)
           B.4.2.8 SCREENSAVER (not supported)
           B.4.2.9 GLX (supported)
           B.4.2.10 RENDER (supported)
           B.4.2.11 Summary
        B.4.3 Additional Testing with the X Test Suite
           B.4.3.1 XFree86 without XTEST
           B.4.3.2 XFree86 with XTEST
           B.4.3.3 Xdmx with XTEST, without Xinerama, without GLX
           B.4.3.4 Xdmx with XTEST, with Xinerama, without GLX
           B.4.3.5 Xdmx with XTEST, with Xinerama, with GLX
           B.4.3.6 Conclusion
        B.4.4 Dynamic Reconfiguration
           B.4.4.1 Dynamic reconfiguration extension
           B.4.4.2 Bounding box
           B.4.4.3 Sample applications
           B.4.4.4 Additional notes
        B.4.5 Doxygen documentation
        B.4.6 Valgrind
        B.4.7 RATS


  ______________________________________________________________________

  1.  Introduction

  1.1.  The Distributed Multihead X Server

  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.


  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.).


  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.


  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.


  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.


  1.2.  Layout of Paper

  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.


  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.


  2.  Development plan

  This section describes the development plan from approximately June
  2001 through July 2003.



  2.1.  Bootstrap code

  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.


  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.


  Status: The boot strap code is complete.



  2.2.  Input device handling

  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'',


  There are some options as to how the front-end X server gets its core
  input devices:


  1. 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.


     The following options are available for implementing local input
     devices:


     a. 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.


     b. The kdrive 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 gpm 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
        kdrive drivers were not used for the DMX implementation.

     c. 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.


  2. 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.

  3. 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.

  4. Other options were initially explored, but they were all partial
     subsets of the options listed above and, hence, are irrelevant.


  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.


  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.


  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):

  1. A "dummy" device drive that never generates events.

  2. "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):

     o  Linux keyboard

     o  Linux serial mouse (MS)

     o  Linux PS/2 mouse

     o  USB keyboard

     o  USB mouse

     o  USB generic device (e.g., joystick, gamepad, etc.)


  3. "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.

  4. "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.



  2.3.  Output device handling

  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.


  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.


  2.3.1.  Initialization

  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.


  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.


  2.3.2.  Handling rendering requests

  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:


  1. 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.


     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.


     The initial DMX implementation used a shadow framebuffer by
     default.


  2. 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.


     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.


     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).



  Status: Both the shadow framebuffer and Xnest-style code is complete.



  2.4.  Optimizing DMX

  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.


  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).


  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.


  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.


  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.


  Other potential optimizations will be determined from the performance
  analysis.

  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.


  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.


  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.



  2.5.  DMX X extension support

  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.


  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:

  1. Screen information (clipping rectangle for each screen relative to
     the virtual screen)

  2. Window information (window IDs and clipping information for each
     back-end window that corresponds to each DMX window)

  3. Input device information (mappings from DMX device IDs to back-end
     device IDs)

  4. Force window creation (so that a client can override the server-
     side lazy window creation optimization)

  5. Reconfiguration (so that a client can request that a screen
     position be changed)

  6. Addition and removal of back-end servers and back-end and console
     inputs.
  2.6.  Common X extension support

  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.


  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.


  Support for the XTest extension was added during the first development
  phase.


  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.


  2.7.  OpenGL support

  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.


  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.


  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.


  1. 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.

  2. 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.


  These, and other, options will be investigated in this phase of the
  work.


  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.


  Status: OpenGL support by the glxProxy extension was implemented by
  SGI and has been integrated into the DMX code base.



  3.  Current issues

  In this sections the current issues are outlined that require further
  investigation.


  3.1.  Fonts

  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.


  3.2.  Zero width rendering primitives

  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.


  3.3.  Output scaling

  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.



  3.4.  Per-screen colormaps

  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.


  A.  Background

  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.


  A.1.  Core input device handling

  The following is a description of how core input devices are handled
  by an X server.


  A.1.1.  InitInput()

  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().


  InitInput() usually has implementation specific code to determine
  which input devices are available.  For each input device it will be
  using, it calls AddInputDevice():


     AddInputDevice()
        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.


  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).


     Register{Pointer,Keyboard}Device()
        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.
  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.


     miRegisterPointerDevice()
        This MI function registers the core pointer's input handle with
        with the miPointer code.


  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():


     mieqInit()
        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.


  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.)


  A.1.2.  InitAndStartDevices()

  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.


  Each registered device is initialized by calling its callback
  (dev->deviceProc) with the DEVICE_INIT argument:


     (*dev->deviceProc)(dev, DEVICE_INIT)
        This function initializes the device structs with core
        information relevant to the device.


        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.


        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).


  Each initialized device is enabled by calling EnableDevice():


     EnableDevice()
        EnableDevice() calls the device callback with DEVICE_ON:

        (*dev->deviceProc)(dev, DEVICE_ON)
           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.


        EnableDevice() then adds the device handle to the X server's
        global list of enabled devices.


  InitAndStartDevices() then verifies that a valid core keyboard and
  pointer has been initialized and enabled.  It returns failure if
  either are missing.


  A.1.3.  devReadInput()

  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).


  Events are queued by calling mieqEnqueue():


     mieqEnqueue()
        This MI function is used to add input events to the event queue.
        It is simply passed the event to be queued.


  The cursor position should be updated when motion events are enqueued,
  by calling either miPointerAbsoluteCursor() or miPointerDeltaCursor():


     miPointerAbsoluteCursor()
        This MI function is used to move the cursor to the absolute
        coordinates provided.

     miPointerDeltaCursor()
        This MI function is used to move the cursor relative to its
        current position.


  A.1.4.  ProcessInputEvents()

  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.


  Enqueued events are processed by mieqProcessInputEvents() and passed
  to the DIX layer for transmission to clients:


     mieqProcessInputEvents()
        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.

     miPointerUpdate()
        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.



  A.1.5.  DisableDevice()

  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.


  DisableDevice() calls the device's callback function with DEVICE_OFF:


     (*dev->deviceProc)(dev, DEVICE_OFF)
        This typically closes the relevant physical device, and when
        appropriate, unregisters the device's file descriptor (or
        equivalent) as a valid input source.


  DisableDevice() then removes the device handle from the X server's
  global list of enabled devices.



  A.1.6.  CloseDevice()

  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.


  CloseDevice() calls the device's callback function with DEVICE_CLOSE:


     (*dev->deviceProc)(dev, DEVICE_CLOSE)
        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.

  CloseDevice() then frees the data structures that were allocated for
  the device when it was registered/initialized.



  A.1.7.  LegalModifier()

  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.



  A.2.  Output handling

  The following sections describe the main functions required to
  initialize, use and close the output device(s) for each screen in the
  X server.


  A.2.1.  InitOutput()

  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.


  The primary tasks for this function are outlined below:


  1. Parse configuration info: 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.

  2. Initialize screen info: 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.

  3. Set pixmap formats: 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.

  4. Unify screen info: 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.

  Once these tasks are complete, the valid screens are known and each of
  these screens can be initialized by calling AddScreen().


  A.2.2.  AddScreen()

  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.


  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.


  A.2.3.  ScreenInit()

  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).


  The screen init function usually calls several functions to perform
  certain screen initialization functions.  They are described below:


     {mi,*fb}ScreenInit()
        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.


        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().


     miInitializeBackingStore()
        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.


     miDCInitialize()
        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.


  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.

  A.2.4.  CloseScreen()

  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.


  A.2.5.  GC operations

  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.


  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.


  Note that some pointers to functions that draw to the screen are
  stored in the Screen structure.  They include GetImage(), GetSpans(),
  PaintWindowBackground(), PaintWindowBorder(), CopyWindow() and
  RestoreAreas().


  A.2.6.  Xnest

  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.


  The Xnest server implements all of the standard input and output
  initialization steps outlined above.


     InitOutput()
        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.


        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.
     ScreenInit()
        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.


     CloseScreen()
        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.


     GC operations
        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.


        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.


        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.


  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.


  A.2.7.  Shadow framebuffer

  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.


  There are two main entry points to the shadow framebuffer code:


     shadowAlloc(width, height, bpp)
        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.


     shadowInit(pScreen, updateProc, windowProc)
        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).


  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.


  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.



  A.3.  Xinerama

  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.


  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.


  The following is a code-level description of how Xinerama functions.


  Note: Because the Xinerama extension was originally called the
  PanoramiX extension, many of the Xinerama functions still have the
  PanoramiX prefix.


     PanoramiXExtensionInit()
        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.


        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.


        The Xinerama extension is registered by calling AddExtension().


        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.


        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).


        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.


     PanoramiXConsolidate()
        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.


        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.


     PanoramiXCreateConnectionBlock()
        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.


        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 xdpyinfo shows).
        The connection block is initialized with the combined single
        screen values that were calculated in the above two functions.


        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().


  A.3.1.  Xinerama-specific changes to the DIX code

  There are a few types of Xinerama-specific changes within the DIX
  code.  The main ones are described here.


  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.


  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.


  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.


  A.3.2.  Xinerama-specific changes to the MI code

  The only Xinerama-specific change to the MI code is in
  miSendExposures() to handle the coordinate (and window ID) translation
  for expose events.



  A.3.3.  Intercepted DIX core requests

  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.



  B.  Development Results

  In this section the results of each phase of development are
  discussed.  This development took place between approximately June
  2001 and July 2003.


  B.1.  Phase I

  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.


  B.1.1.  Scope

  The goal of Phase I is to provide fundamental functionality that can
  act as a foundation for ongoing work:

  1. Develop the proxy X server

     o  The proxy X server will operate on the X11 protocol and relay
        requests as necessary to correctly perform the request.

     o  Work will be based on the existing work for Xinerama and Xnest.

     o  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.

     o  The multiple screen layout (including support for overlapping
        screens) will be user configurable via a configuration file or
        through the configuration tool.

  2. Develop graphical configuration tool

     o  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.

  3. Pass the X Test Suite

     o  The X Test Suite covers the basic X11 operations.  All tests
        known to succeed must correctly operate in the distributed X
        environment.


  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).


  B.1.2.  Results

  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.


  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.


  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.


  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 -configfile and -config command-line
  options can be used to start Xdmx using a configuration file.


  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.


  B.1.3.  X Test Suite

  B.1.3.1.  Introduction

  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.

  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.


  B.1.3.2.  Expected Failures for a Single Head

  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:

  XDrawArc: Tests 42, 63, 66, 73
  XDrawArcs: Tests 45, 66, 69, 76



  The following failures occur because of the high-level X server
  implementation:

  XLoadQueryFont: Test 1
  XListFontsWithInfo: Tests 3, 4
  XQueryFont: Tests 1, 2



  The following test fails when running the X server as root under Linux
  because of the way directory modes are interpreted:

  XWriteBitmapFile: Test 3



  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.


  B.1.3.3.  Expected Failures for Xinerama

  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.

  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.

  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:

  These failures were noted with multiple Xinerama configurations:

  XCopyPlane: Tests 13, 22, 31 (well-known Xinerama implementation issue)
  XSetFontPath: Test 4
  XGetDefault: Test 5
  XMatchVisualInfo: Test 1



  These failures were noted only when using one dual-head video card
  with a 4.2.99.x XFree86 server:

  XListPixmapFormats: Test 1
  XDrawRectangles: Test 45



  These failures were noted only when using two video cards from
  different vendors with a 4.1.99.x XFree86 server:

  XChangeWindowAttributes: Test 32
  XCreateWindow: Test 30
  XDrawLine: Test 22
  XFillArc: Test 22
  XChangeKeyboardControl: Tests 9, 10
  XRebindKeysym: Test 1



  B.1.3.4.  Additional Failures from Xdmx

  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:

  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)



  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.


  B.1.3.5.  Summary and Future Work

  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.

  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.



  B.1.4.  Fonts

  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 the front- and back-end servers must share the exact same font
  path.  There are two ways to help make sure that all servers share the
  same font path:


  1. 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.

  2. 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.


  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.


  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.


  B.1.5.  Performance

  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.


  1. 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.

  2. Sending drawing requests to only the screens that they overlap
     should improve performance.


  B.1.6.  Pixmaps

  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.



  B.2.  Phase II

  The second phase of development concentrates on performance
  optimizations.  These optimizations are documented here, with x11perf
  data to show how the optimizations improve performance.


  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.


  B.2.1.  Moving from XFree86 4.1.99.1 to 4.2.0.0

  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:

  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)



  And the following tests were noted to be more than 10% slower:

  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)



  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 x11perf tests.


  B.2.2.  Global changes

  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:



  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)



  The following tests were noted to be more than 10% slower:

  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)



  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.


  B.2.3.  XSync() Batching

  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.


  Out of more than 300 x11perf 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.


  The following tests were noted to be more than 10% slower with XSync()
  batching on:

  0.88   500x500 tiled rectangle (161x145 tile)
  0.89   Copy 500x500 from window to window



  B.2.4.  Offscreen Optimization

  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.


  Out of more than 300 x11perf 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:

  0.88   Hide/expose window via popup (4 kids)
  0.89   Resize unmapped window (75 kids)



  B.2.5.  Lazy Window Creation Optimization

  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.


  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.


  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.


  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.



  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.


  This optimization improved the following x11perf tests by more than
  10%:

  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)



  B.2.6.  Subdividing Rendering Primitives

  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.


  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.


  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.


  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.


  This optimization improved the following x11perf tests by more than
  10%:

  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)



  The following test was noted to be more than 10% slower with this
  optimization:

  0.88   10-pixel fill chord partial circle



  B.2.7.  Summary of x11perf Data

  With all of the optimizations on, 53 x11perf 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 x11perf tests.)


  The following table summarizes relative x11perf test changes for all
  optimizations individually and collectively.  Note that some of the
  optimizations have a synergistic effect when used together.



  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)



  B.2.8.  Profiling with OProfile

  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 gprof, 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 x11perf test individually.


  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 gprof output.  This
  investigation has not produced results that yield performance
  increases in x11perf numbers.



  B.2.9.  X Test Suite

  The X Test Suite was run on the fully optimized DMX server using the
  configuration described above.  The following failures were noted:

  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.



  B.3.  Phase III

  During the third phase of development, support was provided for the
  following extensions: SHAPE, RENDER, XKEYBOARD, XInput.


  B.3.1.  SHAPE

  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.


  B.3.2.  RENDER

  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.


  B.3.3.  XKEYBOARD

  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.


  B.3.4.  XInput

  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.


  Currently, back-end extension devices are not available as Xdmx
  extension devices, but this limitation should be removed in the
  future.


  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.


  B.3.5.  DPMS

  The DPMS extension is exported but does not do anything at this time.


  B.3.6.  Other Extensions

  The LBX, SECURITY, XC-APPGROUP, and XFree86-Bigfont extensions do not
  require any special Xdmx support and have been exported.


  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 not supported at
  this time, but will be evaluated for inclusion in future DMX releases.
  See below for additional work on extensions after Phase III.


  B.4.  Phase IV

  B.4.1.  Moving to XFree86 4.3.0

  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.


  B.4.2.  Extensions

  B.4.2.1.  XC-MISC (supported)

  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.


  B.4.2.2.  Extended-Visual-Information (supported)

  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 hw/dmx/examples/evi example
  program.  Note that this extension is not Xinerama-aware -- it will
  return visual information for each screen even though Xinerama is
  causing the X server to export a single logical screen.


  B.4.2.3.  RES (supported)

  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 hw/dmx/examples/res program.  The X Test
  Suite passed and failed the exact same tests before and after this
  extension was enabled.


  B.4.2.4.  BIG-REQUESTS (supported)

  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.


  B.4.2.5.  XSYNC (supported)

  This extension provides facilities for two different X clients to
  synchronize their requests.  This extension was minimally tested with
  xdpyinfo and the X Test Suite passed and failed the exact same tests
  before and after this extension was enabled.


  B.4.2.6.  XTEST, RECORD, DEC-XTRAP (supported) and XTestExtension1
  (not supported)

  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 rcrdtest
  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.


  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.


  The DEC-XTRAP extension is available from Xdmx and has been tested
  with the xtrap* tools which are distributed as standard X11R6 clients.


  The XTestExtension1 is not 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).


  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:

     XRECORD
        Martha Zimet. Extending X For Recording.  8th Annual X Technical
        Conference Boston, MA January 24-26, 1994.

     DEC-XTRAP
        Dick Annicchiarico, Robert Chesler, Alan Jamison. XTrap
        Architecture. Digital Equipment Corporation, July 1991.

     XTestExtension1
        Larry Woestman. X11 Input Synthesis Extension Proposal. Hewlett
        Packard, November 1991.


  B.4.2.7.  MIT-MISC (not supported)

  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 not support MIT-MISC.


  B.4.2.8.  SCREENSAVER (not supported)

  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, beforelight behaved as
  expected.  However, when Xinerama was active, beforelight did not
  behave as expected.  Further, when this extension is not active,
  xscreensaver (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.

  B.4.2.9.  GLX (supported)

  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.


  B.4.2.10.  RENDER (supported)

  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.


  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.


  B.4.2.11.  Summary

  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.


  The following extensions are not 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.


  B.4.3.  Additional Testing with the X Test Suite

  B.4.3.1.  XFree86 without XTEST

  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 not 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:

  XListPixmapFormats: Test 1
  XChangeKeyboardControl: Tests 9, 10
  XGetDefault: Test 5
  XRebindKeysym: Test 1



  B.4.3.2.  XFree86 with XTEST

  When using the XTEST extension, the XFree86 4.3.0 server reported the
  following errors:

  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



  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.


  B.4.3.3.  Xdmx with XTEST, without Xinerama, without GLX

  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):

  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



  B.4.3.4.  Xdmx with XTEST, with Xinerama, without GLX

  With Xinerama, using the XTEST extension, the following errors were
  reported from Xdmx:

  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



  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.


  B.4.3.5.  Xdmx with XTEST, with Xinerama, with GLX

  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):

  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


  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 con-
  clusion 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.


  Further, when hardware rendering is disabled on the back-end displays,
  many of the errors in the third set are eliminated, leaving only:

  XClearArea: Test 8
  XCopyArea: Test 4, 5, 11, 14, 17, 23, 25, 27, 30
  XCopyPlane: Test 6, 7, 10, 19, 22, 31



  B.4.3.6.  Conclusion

  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.)


  B.4.4.  Dynamic Reconfiguration

  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.


  B.4.4.1.  Dynamic reconfiguration extension

  The application interface to DMX's dynamic reconfiguration is through
  a function in the DMX extension library:

  Bool DMXReconfigureScreen(Display *dpy, int screen, int x, int y)


  where dpy is DMX server's display, screen is the number of the screen
  to be reconfigured, and x and y are the new upper, left-hand coordi-
  nates of the screen to be reconfigured.


  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.


  B.4.4.2.  Bounding box

  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.


  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.


  This fixed bounding box limitation will be addressed in a future
  development phase.


  B.4.4.3.  Sample applications

  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.


  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.


  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 dmxreconfig.c for details.


  B.4.4.4.  Additional notes

  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).


  B.4.5.  Doxygen documentation

  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.


  B.4.6.  Valgrind

  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:

  1. 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.

  2. 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.

  3. 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.


  B.4.7.  RATS

  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:

  1. 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.

  2. 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.

  3. 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).



