                               DRI User Guide

          VA Linux Systems, Inc. Professional Services - Graphics.

                                15 June 2001

1.  Preamble

1.1  Copyright

Copyright © 2000-2001 by VA Linux Systems, Inc.  All Rights Reserved.

Permission is granted to make and distribute verbatim copies of this document
provided the copyright notice and this permission notice are preserved on all
copies.

1.2  Trademarks

OpenGL is a registered trademark and SGI is a trademark of Silicon Graphics,
Inc.  Unix is a registered trademark of The Open Group.  The `X' device and X
Window System are trademarks of The Open Group.  XFree86 is a trademark of
The XFree86 Project.  Linux is a registered trademark of Linus Torvalds.
Intel is a registered trademark of Intel Corporation.  3Dlabs, GLINT, and
Oxygen are either registered trademarks or trademarks of 3Dlabs Inc. Ltd.
3dfx, Voodoo3, Voodoo4, and Voodoo5 are registered trademarks of 3dfx Inter-
active, Incorporated.  Matrox is a registered trademark of Matrox Electronic
Systems Ltd.  ATI Rage and Radeon are registered trademarks of ATI Technolo-
gies, Inc.  All other trademarks mentioned are the property of their respec-
tive owners.

2.  Introduction

With XFree86 4.x and the Direct Rendering Interface (DRI), hardware acceler-
ated 3D graphics can be considered a standard feature on Linux workstations.
Support for other operating systems, such as FreeBSD, is underway.

This document describes how to use the DRI system and troubleshoot problems
which may occur.  Readers should have a basic understanding of Linux, X and
OpenGL.  See the resources section at the end for more documentation and
software downloads.

This document does not cover compilation or installation of XFree86 4.x.  It
is assumed that you've already installed a Linux distribution which includes
XFree86 4.x or that you're an experienced Linux developer who has compiled
the DRI for himself.  DRI download, compilation and installation instructions
can be found at http://dri.sourceforge.net/DRIcompile.html

Edits, corrections and updates to this document may be mailed to <brian@tung-
stengrahpics.com>.

3.  Supported Architectures & Hardware

3.1  CPU Architectures

The architectures currently supported by the DRI have grown from the initial
Intel i386 systems to now include the Alpha Processor and the Sun SPARC
machines.

Intel's SSE (a.k.a. Katmai) instructions are used in optimized vertex trans-
formation functions in Mesa-based drivers.  This requires a recent Linux ker-
nel both at compile and runtime.  See the DRI Compile Guide for compile-time
requirements.  At runtime a check is made to determine if the CPU can execute
SSE instructions.  They're disabled otherwise.

AMD's 3DNow! instructions are also used in optimized vertex transformation
functions in the Mesa-based DRI drivers.  3DNow! is supported in most ver-
sions of Linux.  Like the SSE optimizations, a runtime check is made to
determine if the CPU can execute 3DNow! instructions.

Alpha-based systems can use Compaq's optimized math library for improved 3D
performance.  See the DRI Compilation Guide for details.

3.2  Graphics Hardware

XFree86 4.2 (or later versions) includes 3D acceleration for the following
graphics hardware:

   o 3dfx, supported on Intel x86, AMD and Alpha:

        o Voodoo5 5500

        o Voodoo4 4500

        o Voodoo3 3500 TV

        o Voodoo3 3000 AGP

        o Voodoo3 3000 PCI

        o Voodoo3 2000 AGP

        o Voodoo3 2000 PCI

        o Voodoo Banshee

        o Velocity 100/200

     There are many configurations of 3dfx cards on the market.  Not all have
     been tested.

   o Matrox, supported on Intel x86 and AMD:

        o Matrox G200

        o Matrox G400

   o Intel i810/i815/i830 (motherboard chipsets)

        o i810

        o i810-dc100

        o i810e

        o i815

        o i830

   o ATI Rage 128, supported on Intel x86, AMD and Alpha:

        o Rage Fury

        o Rage Magnum

        o XPERT 2000

        o XPERT 128

        o XPERT 99

        o All-in-Wonder 128

        o Rage 128 PCI (Alpha-based systems)

     Note that both PCI and AGP versions of Rage 128 based cards are sup-
     ported at this time.

   o ATI Radeon, supported on Intel x86, AMD and Alpha:

        o Radeon SDR AGP

        o Radeon DDR AGP

        o Radeon 32MB SDR PCI (Alpha-based systems)

        o Radeon 7000, M6 (RV100)

        o Radeon 7200 (R100)

        o Radeon 7500, M7 (RV200)

        o Radeon 8500, 9100 (R200)

        o Radeon 9000, M9 (RV250)

   o 3Dlabs, supported on Intel x86 and AMD:

        o Oxygen GMX 2000 (MX/Gamma based).  Note:  this driver is no longer
          being actively developed.

Support for other hardware is underway.  Most of the DRI development work is
funded by contracts with IHVs.  These contracts often prevent us from
announcing drivers before they're released.  Queries about upcoming drivers
may not be answerable.

4.  Prerequisite Software

   o The DRI is available in XFree86 4.0 and later.

   o Some hardware drivers require specific versions of the Linux kernel for
     AGP support, etc.  See section 10 for specifics.

   o You DO NOT need to install Mesa separately.  The parts of Mesa needed
     for hardware acceleration are already in the XFree86/DRI project.

5.  Kernel Modules

3D hardware acceleration requires a DRI kernel module that's specific to your
graphics hardware.

The DRI kernel module version must exactly match your running kernel version.
Since there are so many versions of the kernel, it's difficult to provide
precompiled kernel modules.

While the Linux source tree includes the DRI kernel module sources, the lat-
est DRI kernel sources will be found in the DRI source tree.

See the DRI Compilation Guide for information on compiling the DRI kernel
modules.

XFree86 4.0.1 added automatic kernel module loading to the X server.  On
Linux, the X server uses modprobe to load kernel modules.  In Linux 2.4.x the
DRM kernel modules should be kept in /lib/modules/2.4.x/ker-
nel/drivers/char/drm/ for automatic loading to work.

Optionally, DRM kernel modules can be loaded manually with insmod prior to
starting the X server.

You can verify that the kernel module was installed with lsmod, checking the
X server startup log, and checking that /proc/dri/0 exists.

6.  XF86Config file

The XFree86 configuration file is usually found in /etc/X11/XF86Config.  This
section describes the parts which must be specially set for the DRI.

First, the XF86Config file must load the GLX and DRI modules:

          Section "Module"
          ...
          # This loads the GLX module
              Load       "glx"
          # This loads the DRI module
              Load       "dri"
          EndSection

Next, the DRI section can be used to restrict access to direct rendering.  A
client can only use direct rendering if it has permission to open the
/dev/dri/card? file(s).  The permissions on these DRI device files is con-
trolled by the "DRI" section in the XF86Config file.

If you want all of the users on your system to be able to use direct-render-
ing, then use a simple DRI section like this:

          Section "DRI"
               Mode 0666
          EndSection

This section will allow any user with a current connection to the X server to
use direct rendering.

If you want to restrict the use of direct-rendering to a certain group of
users, then create a group for those users by editing the /etc/group file on
your system.  For example, you may want to create a group called xf86dri and
place two users (e.g., fred and jane) in that group.  To do that, you might
add the following line to /etc/group:

             xf86dri:x:8000:fred,jane

You have to be careful that the group id (8000 in this example) is unique.

Then you would use the following DRI section:

             Section "DRI"
                  Group "xf86dri"
                  Mode 0660
             EndSection

This would limit access to direct-rendering to those users in the xf86dri
group (fred and jane in this example).  When other users tried to use direct
rendering, they would fall back to unaccelerated indirect rendering.

[Note that there is a known bug in XFree86 4.0 that prevents some changes to
the DRI section from taking effect.  Until this bug is fixed, if you change
the DRI section, please also remove the /dev/dri directory with the rm -rf
/dev/dri command.]

Finally, the XF86Config file needs Device and Screen sections specific to
your hardware.  Look in section 10: Hardware-Specific Information and Trou-
bleshooting for details.

7.  Memory usage

Using the 3D features of a graphics card requires more memory than when it's
just used as a 2D device.  Double buffering, depth buffering, stencil
buffers, textures, etc. all require extra graphics memory.  These features
may require four times the memory used for a simple 2D display.

If your graphics card doesn't have a lot of memory (less than 16MB, for exam-
ple), you may have to reduce your screen size and/or color depth in order to
use 3D features.  Reducing the screen resolution will also leave more space
for texture images, possibly improving 3D performance.  If, for example, you
play Quake3 at 1024x768 but start your display at 1600x1200 you might con-
sider restarting X at 1024x768 in order to maximize your texture memory
space.

The documentation included with your card should have information about maxi-
mum screen size when using 3D.

8.  Using 3D Acceleration

This section describes how to link your application with libGL.so and verify
that you are in fact using 3D acceleration.

8.1  libGL.so

Your OpenGL program must link with the libGL.so.1.2 library provided by
XFree86.  The libGL.so.1.2 library contains a GLX protocol encoder for indi-
rect/remote rendering and DRI code for accessing hardware drivers.  In par-
ticular, be sure you're not using libGL.so from another source such as Mesa
or the Utah GLX project.

Unless it was built in a special way, the libGL.so library does not contain
any 3D hardware driver code.  Instead, libGL.so dynamically loads the appro-
priate 3D driver during initialization.

Most simple OpenGL programs also use the GLUT and GLU libraries.  A source
for these libraries is listed in the Resources section below.

8.2  Compiling and linking an OpenGL program

A simple GLUT/OpenGL program may be compiled and linked as follows:

             gcc program.c -I/usr/local/include -L/usr/local/lib -L/usr/X11R6/lib -lglut -lGLU -lGL -o program

The -I option is used to specify where the GL/glut.h (and possibly the
GL/gl.h and GL/glu.h) header file may be found.

The -L options specify where the libglut.so and the X libraries are located.
libGL.so and libGLU.so should be in /usr/lib, as specified by the
Linux/OpenGL ABI standard.

The -lglut -lGLU -lGL arguments specify that the application should link with
the GLUT, GLU and GL libraries, in that order.

8.3  Running your OpenGL program

Simply typing ./program in your shell should execute the program.

If you get an error message such as

             gears: error in loading shared libraries: libGL.so.1: cannot
             open shared object file: No such file or directory

if means that the libGL.so.1 file is not the right location.  Proceed to the
trouble shooting section.

8.4  libOSMesa.so

OSMesa (Off-Screen Mesa) is an interface and driver for rendering 3D images
into a user-allocated block of memory rather than an on-screen window.  It
was originally developed for Mesa before Mesa became part of the XFree86/DRI
project.  It can now be used with the XFree86/DRI libGL.so as well.

libOSMesa.so implements the OSMesa interface and it must be linked with your
application if you want to use the OSMesa functions.  You must also link with
libGL.so.  For example:

             gcc osdemo.c -lOSMesa -lGLU -lGL -o osdemo

In stand-alone Mesa this interface was compiled into the monolithic libGL.so
(formerly libMesaGL.so) library.  In XFree86 4.0.1 and later this interface
is implemented in a separate library.

8.5  glxinfo

glxinfo is a useful program for checking which version of libGL you're using
as well as which DRI-based driver.  Simply type glxinfo and examine the
OpenGL vendor, renderer, and version lines.  Among the output you should see
something like this:

               OpenGL vendor string: VA Linux Systems, Inc.
               OpenGL renderer string: Mesa DRI Voodoo3 20000224
               OpenGL version string: 1.2 Mesa 3.4

or this:

               OpenGL vendor string: VA Linux Systems, Inc.
               OpenGL renderer string: Mesa GLX Indirect
               OpenGL version string: 1.2 Mesa 3.4

The first example indicates that the 3dfx driver is using Voodoo3 hardware.
The second example indicates that no hardware driver was found and indirect,
unaccelerated rendering is being used.

If you see that indirect rendering is being used when direct rendering was
expected, proceed to the troubleshooting section.

glxinfo also lists all of the GLX-enhanced visuals available so you can
determine which visuals are double-bufferd, have depth (Z) buffers, stencil
buffers, accumulation buffers, etc.

8.6  Environment Variables

The libGL.so library recognizes three environment variables.  Normally, none
of them need to be defined.  If you're using the csh or tcsh shells, type
setenv VARNAME value to set the variable.  Otherwise, if you're using sh or
bash, type export VARNAME=value.

  1.  LIBGL_DEBUG, if defined will cause libGL.so to print error and diagnos-
      tic messages.  This can help to solve problems.  Setting LIBGL_DEBUG to
      verbose may provide additional information.

  2.  LIBGL_ALWAYS_INDIRECT, if defined this will force libGL.so to always
      use indirect rendering instead of hardware acceleration.  This can be
      useful to isolate rendering errors.

  3.  LIBGL_DRIVERS_PATH can be used to override the default directories
      which are searched for 3D drivers.  The value is one or more paths sep-
      arated by colons.  In a typical XFree86 installation, the 3D drivers
      should be in /usr/X11R6/lib/modules/dri/ and LIBGL_DRIVERS_PATH need
      not be defined.  Note that this feature is disabled for set-uid pro-
      grams.  This variable replaces the LIBGL_DRIVERS_DIR env var used in
      XFree86 4.0.

  4.  MESA_DEBUG, if defined, will cause Mesa-based 3D drivers to print user
      error messages to stderr.  These are errors that you'd otherwise detect
      by calling glGetError.

Mesa-based drivers (this includes most of the drivers listed above) also
observe many of the existing Mesa environment variables.  These include the
MESA_DEBUG and MESA_INFO variables.

9.  General Trouble Shooting

This section contains information to help you diagnose general problems.  See
below for additional information for specific hardware.

9.1  Bus Mastering

DMA-based DRI drivers (that's most DRI drivers) cannot function unless bus
mastering is enabled for your graphics card.  By default, some systems don't
having bus mastering on.  You should enable it in your BIOS.

Alternately, you can check the status of bus mastering and change the setting
from within Linux.  There may be similar procedures for other operating sys-
tems.

Run lspci (as root) and find the information describing your graphics
adapter.  For example:

         00:00.0 Host bridge: Intel Corporation 440BX/ZX - 82443BX/ZX Host bridge (rev 03)
         00:01.0 PCI bridge: Intel Corporation 440BX/ZX - 82443BX/ZX AGP bridge (rev 03)
         00:07.0 ISA bridge: Intel Corporation 82371AB PIIX4 ISA (rev 02)
         00:07.1 IDE interface: Intel Corporation 82371AB PIIX4 IDE (rev 01)
         00:07.2 USB Controller: Intel Corporation 82371AB PIIX4 USB (rev 01)
         00:07.3 Bridge: Intel Corporation 82371AB PIIX4 ACPI (rev 02)
         00:11.0 Ethernet controller: Intel Corporation 82557 [Ethernet Pro 100] (rev 08)
         00:12.0 SCSI storage controller: Symbios Logic Inc. (formerly NCR) 53c895 (rev 02)
         00:14.0 Multimedia audio controller: Ensoniq ES1371 [AudioPCI-97] (rev 08)
         01:00.0 VGA compatible controller: 3Dfx Interactive, Inc.: Unknown device 0009 (rev 01)

The bus, device, and function number comprise the device id, which is conven-
tionally written in the form bus:dev.func, or in this case 01:00.0.

Use the setpci command to examine bit two of register 4 for your graphics
card.  This will indicate whether or not bus mastering is enabled.

             setpci -s 01:00.0 4.w

A hexadecimal value will be printed.  Convert the least significant digit to
binary.  For example, if you see 3, that's 0011 in binary (bit two is 0).  If
you see 7, that's 0111 in binary (bit two is 1).  In the first example, bus
mastering is disabled.  It's enabled in the second example.

The following shell script will enabled bus mastering for your graphics card
and host bridge.  Run it as root.

         #!/bin/bash
         dev=01:00.0   # change as appropriate
         echo Enabling bus mastering on device $dev
         setpci -s $dev 4.w=$(printf %x $((0x$(setpci -s $dev 4.w)|4)))
         dev=00:00.0
         echo Enabling bus mastering on host bridge $dev
         setpci -s $dev 4.w=$(printf %x $((0x$(setpci -s $dev 4.w)|4)))

You can check if this worked by running the first setpci command again.

9.2  The X Server

  1.  Before you start the X server, verify the appropriate 3D kernel module
      is installed.  Type lsmod and look for the appropriate kernel module.
      For 3dfx hardware you should see tdfx, for example.

  2.  Verify you're running XFree86 4.0 (or newer) and not an older version.
      If you run xdpyinfo and look for the following line near the top:

                       vendor release number:    4000

  3.  Verify that your XF86Config file (usually found at /etc/X11/XF86Config)
      loads the glx and dri modules and has a DRI section.

      See the Software Resources section below for sample XF86Config files.

  4.  Examine the messages printed during X server startup and check that the
      DRM module loaded.  Using the Voodoo3 as an example:

                   (==) TDFX(0): Write-combining range (0xf0000000,0x2000000)
                   (II) TDFX(0): Textures Memory 7.93 MB
                   (0): [drm] created "tdfx" driver at busid "PCI:1:0:0"
                   (0): [drm] added 4096 byte SAREA at 0xc65dd000
                   (0): [drm] mapped SAREA 0xc65dd000 to 0x40013000
                   (0): [drm] framebuffer handle = 0xf0000000
                   (0): [drm] added 1 reserved context for kernel
                   (II) TDFX(0): [drm] Registers = 0xfc000000
                   (II) TDFX(0): visual configs initialized
                   (II) TDFX(0): Using XFree86 Acceleration Architecture (XAA)
                           Screen to screen bit blits
                           Solid filled rectangles
                           8x8 mono pattern filled rectangles
                           Indirect CPU to Screen color expansion
                           Solid Lines
                           Dashed Lines
                           Offscreen Pixmaps
                           Driver provided NonTEGlyphRenderer replacement
                           Setting up tile and stipple cache:
                                   10 128x128 slots
                   (==) TDFX(0): Backing store disabled
                   (==) TDFX(0): Silken mouse enabled
                   (0): X context handle = 0x00000001
                   (0): [drm] installed DRM signal handler
                   (0): [DRI] installation complete
                   (II) TDFX(0): direct rendering enabled

  5.  After the X server has started, verify that the required X server
      extensions are loaded.  Run xdpyinfo and look for the following entries
      in the extensions list:

                  GLX
                  SGI-GLX
                  XFree86-DRI

9.3  Linking, running and verifying 3D acceleration

After you've verified that the X server and DRI have started correctly it's
time to verify that the GL library and hardware drivers are working cor-
rectly.

  1.  Verify that you're using the correct libGL.so library with ldd.  The
      /usr/lib and /usr/X11R6/lib directories are expected locations for
      libGL.so.

      Example:

                   % ldd /usr/local/bin/glxinfo
                           libglut.so.3 => /usr/local/lib/libglut.so.3 (0x40019000)
                           libGLU.so.1 => /usr/local/lib/libGLU.so.1 (0x40051000)
                           libGL.so.1 => /usr/lib/libGL.so.1 (0x40076000)
                           libXmu.so.6 => /usr/X11R6/lib/libXmu.so.6 (0x402ee000)
                           libXi.so.6 => /usr/X11R6/lib/libXi.so.6 (0x40301000)
                           libm.so.6 => /lib/libm.so.6 (0x40309000)
                           libc.so.6 => /lib/libc.so.6 (0x40325000)
                           libX11.so.6 => /usr/X11R6/lib/libX11.so.6 (0x40419000)
                           libXt.so.6 => /usr/X11R6/lib/libXt.so.6 (0x404bd000)
                           libSM.so.6 => /usr/X11R6/lib/libSM.so.6 (0x40509000)
                           libICE.so.6 => /usr/X11R6/lib/libICE.so.6 (0x40512000)
                           libXext.so.6 => /usr/X11R6/lib/libXext.so.6 (0x40529000)
                           libvga.so.1 => /usr/lib/libvga.so.1 (0x40537000)
                           libpthread.so.0 => /lib/libpthread.so.0 (0x4057d000)
                           /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)

  2.  You may also double check that libGL.so is in fact DRI-capable.  Run
      strings libGL.so.1.2 | grep DRI and look for symbols prefixed with
      "XF86DRI", such as "XF86DRIQueryExtension".

  3.  To be safe one should run ldconfig after installing libGL.so to be sure
      the runtime loader will find the proper library.

  4.  Verify that the appropriate 3D driver is in /usr/X11R6/lib/modules/dri/
      For example, the 3dfx driver will be named tdfx_dri.so.

  5.  Set the LIBGL_DEBUG environment variable.  This will cause libGL.so to
      print an error message if it fails to load a DRI driver.  Any error
      message printed should be self-explanatory.

  6.  Run glxinfo.  Note the line labeled "OpenGL renderer string".  It
      should have a value which starts with "Mesa DRI" followed by the name
      of your hardware.

  7.  Older Linux OpenGL applications may have been linked against Mesa's GL
      library and will not automatically use libGL.so.  In some cases, making
      symbolic links from the Mesa GL library to libGL.so.1 will solve the
      problem:

                   ln -s libGL.so.1 libMesaGL.so.3

      In other cases, the application will have to be relinked against the
      new XFree86 libGL.so.

      It is reported that part of the problem is that running ldconfig will
      silently rewrite symbolic links based on the SONAME field in libraries.

If you're still having trouble, look in the next section for information spe-
cific to your graphics card.

10.  Hardware-Specific Information and Troubleshooting

This section presents hardware-specific information for normal use and trou-
bleshooting.

10.1  3dfx Banshee, Voodoo3, Voodoo4 and Voodoo5 Series

10.1.1  Requirements

The 3dfx DRI driver requires special versions of the 3dfx Glide library.
Different versions of Glide are needed for Banshee/Voodoo3 than for
Voodoo4/5.  The Glide libraries can be downloaded from the DRI website.

10.1.2  Configuration

Your XF86Config file's device section must specify the tdfx device.  For
example:

             Section "Device"
                 Identifier  "Voodoo3"
                 VendorName  "3dfx"
                 Driver      "tdfx"
             EndSection

Or,

             Section "Device"
                 Identifier  "Voodoo5"
                 VendorName  "3dfx"
                 Driver      "tdfx"
             EndSection

The Screen section should then reference the Voodoo device:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "Voodoo3"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

Or,

          Section "Screen"
              Identifier  "Screen 1"
              Device      "Voodoo5"
              Monitor     "High Res Monitor"
              DefaultDepth 24
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
              Subsection "Display"
               Depth       24
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

The kernel module for 3dfx hardware is named tdfx.o and should be installed
in /lib/modules/2.4.x/kernel/drivers/char/drm/.  It will be automatically
loaded by the Xserver if needed.

The DRI 3D driver for 3dfx hardware should be in /usr/X11R6/lib/mod-
ules/dri/tdfx_dri.so.  This will be automatically loaded by libGL.so.

The Voodoo5 supports 3D rendering in 16 and 32 bpp modes.  When running in
32bpp mode an 8-bit stencil buffer and 24-bit Z (depth) buffer are offered.
When running in 16bpp mode only a 16-bit Z (depth) buffer is offered and
stencil is implemented in software.

A software-based accumulation buffer is available in both 16 and 32bpp modes.

10.1.3  Troubleshooting

   o If you try to run an OpenGL application and see an error message similar
     to

                gd error (glide): gd error (glide): grSstSelect:  non-existent SSTgd error (glide): grSstSelect:  non-existent SSTS

     it means that you have the wrong version of the Glide library for your
     hardware.

   o 3D acceleration for Banshee and Voodoo3 is only supported in the 16
     bit/pixel screen mode.  Use xdpyinfo to verify that all your visuals are
     depth 16.  Edit your XF86Config file if needed.

   o The /dev/3dfx device is not used for DRI; it's only for Glide on older
     3dfx hardware.

   o Different versions of Glide are needed for Voodoo3 and Voodoo5.  See the
     DRI website's resources page to download the right version of Glide.

   o Voodoo4/5 may be run at 24bpp (instead of 32bpp, the default) but 3D
     acceleration is not supported in that mode.  32bpp mode is fully 3D
     accelerated.

10.1.4  Performance and Features

   o Normally, buffer swapping in double-buffered applications is synchro-
     nized to your monitor's refresh rate.  This may be overridden by setting
     the FX_GLIDE_SWAPINTERVAL environment variable.  The value of this vari-
     able indicates the maximum number of swap buffer commands can be
     buffered.  Zero allows maximum frame rate.

   o On Voodoo4/5, rendering with 16-bits/texel textures is faster than using
     32-bit per texel textures.  The internalFormat parameter to glTexImage2D
     can be used to control texel size.  Quake3 and other games let you con-
     trol this as well.

   o The glTexEnv mode GL_BLEND is not directly supported by the Voodoo3
     hardware.  It can be accomplished with a multipass algorithm but it's
     not implemented at this time.  Applications which use that mode, such as
     the Performer Town demo, may become sluggish when falling back to soft-
     ware rendering to render in that mode.

   o The Voodoo3/Banshee driver reverts to software rendering under the fol-
     lowing conditions:

        o Setting GL_LIGHT_MODEL_COLOR_CONTROL to GL_SEPARATE_SPECULAR_COLOR.

        o Enabling line stippling or polygon stippling.

        o Enabling point smoothing or polygon smoothing.

        o Enabling line smoothing when line width is not 1.0.  That is,
          antialiased lines are done in hardware only when the line width is
          1.0.

        o Using 1-D or 3-D texture maps.

        o Using the GL_BLEND texture environment.

        o Using stencil operations.

        o Using the accumulation buffer.

        o Using glBlendEquation(GL_LOGIC_OP).

        o Using glDrawBuffer(GL_FRONT_AND_BACK).

        o Using glPolygonMode(face, GL_POINT) or glPolygonMode(face,
          GL_LINE).

        o Using point size attenuation (i.e. GL_DISTANCE_ATTENUATION_EXT).

        o Using glColorMask(r, g, b, a) when r!=g or g!=b.

   o The Voodoo5 driver reverts to software rendering under the same condi-
     tions Voodoo3 with three exceptions.  First, stencil operations are
     implemented in hardware when the screen is configured for 32 bits/pixel.
     Second, the GL_BLEND texture env mode is fully supported in hardware.
     Third, glColorMask is fully supported in hardware when the screen is
     configured for 32 bits/pixel.

   o As of January, 2001 the second VSA-100 chip on the Voodoo5 is not yet
     operational.  Therefore, the board isn't being used to its full capac-
     ity.  The second VSA-100 chip will allow Scan-Line Interleave (SLI) mode
     for full-screen applications and games, potentially doubling the sys-
     tem's fill rate.  When the second VSA-100 chip is activated glGet-
     String(GL_RENDERER) will report Voodoo5 instead of Voodoo4.

   o The lowest mipmap level is sometimes miscolored in trilinear- sampled
     polygons.

   o The GL_EXT_texture_env_combine extension is supported on the Voodoo4 and
     Voodoo5.

10.1.5  Known Problems

   o The lowest mipmap level is sometimes miscolored in trilinear- sampled
     polygons (Voodoo3/Banshee).

   o Fog doesn't work with orthographic projections.

   o The accuracy of blending operations on Voodoo4/5 isn't always very good.
     If you run Glean, you'll find some test failures.

   o The Glide library cannot be used directly; it's only meant to be used
     via the tdfx DRI driver.

   o SSystem has problems because of poorly set near and far clipping planes.
     The office.unc Performer model also suffers from this problem.

10.2  Intel i810

10.2.1  Requirements

A kernel with AGP GART support (such as Linux 2.4.x) is needed.

10.2.2  Configuration

Your XF86Config file's device section must specify the i810 device, and spec-
ify a usable amount of video ram to reserve.

             Section "Device"
                 Identifier  "i810"
                 VendorName  "Intel"
                 Driver      "i810"
              Option     "AGPMode" "1"
              VideoRam    10000
             EndSection

The Screen section should then reference the i810 device:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "i810"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

The kernel module for the i810 is named i810.o and should be installed in
/lib/modules/2.4.x/kernel/drivers/char/drm/.  It will be automatically loaded
by the Xserver if needed.

The DRI 3D driver for the i810 should be in /usr/X11R6/lib/mod-
ules/dri/i810_dri.so.  This will be automatically loaded by libGL.so.

10.2.3  Troubleshooting

   o 3D acceleration for the i810 is only available in the 16 bit/pixel
     screen mode at this time.  32bpp acceleration is not supported by this
     hardware.  Use xdpyinfo to verify that all your visuals are depth 16.
     Edit your XF86Config file if needed.

   o The i810 uses system ram for video and 3d graphics.  The X server will
     ordinarily reserve 4mb of ram for graphics, which is too little for an
     effective 3d setup.  To tell the driver to use a larger amount, specify
     a VideoRam option in the Device section of your XF86Config file.  A num-
     ber between 10000 and 16384 seems adequate for most requirements.  If
     too little memory is available for DMA buffers, back and depth buffers
     and textures, direct rendering will be disabled.

10.2.4  Performance and Features

Basically all of the i810 features which can be exposed through OpenGL 1.2
are implemented.  However, the following OpenGL features are implemented in
software and will be slow:

   o Stencil buffer and accumulation buffer operations

   o Blend subtract, min/max and logic op blend modes

   o glColorMask when any mask is set to false

   o GL_SEPARATE_SPECULAR_COLOR lighting mode

   o glDrawBuffer(GL_FRONT_AND_BACK)

   o Using 1D or 3D textures

   o Using texture borders

10.3  Matrox G200 and G400

10.3.1  Requirements

A kernel with AGP GART support (such as Linux 2.4.x) is needed.

10.3.2  Configuration

Your XF86Config file's device section must specify the mga device:

             Section "Device"
                 Identifier  "MGA"
                 VendorName  "Matrox"
                 Driver      "mga"
              Option     "AGPMode" "1"
              VideoRam    32768
             EndSection

The Screen section should then reference the MGA device:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "MGA"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

To use a 32bpp screen mode, use this Screen section instead:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "MGA"
              Monitor     "High Res Monitor"
              DefaultDepth 24
                 DefaultFbBpp 32
              Subsection "Display"
               Depth       24
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

The kernel module for the G200/G400 is named mga.o and should be installed in
/lib/modules/2.4.x/kernel/drivers/char/drm/.  It will be automatically loaded
by the Xserver if needed.

The DRI 3D driver for the G200/G400 should be in /usr/X11R6/lib/mod-
ules/dri/mga_dri.so.  This will be automatically loaded by libGL.so.

10.3.3  Performance and Features

Software rendering will be used under any of the following conditions:

   o Using glDrawBuffer(GL_FRONT_AND_BACK).

   o Using point, line, or triangle smoothing.

   o Using glLogicOp.

   o Using glPolygonStipple or glLineStipple.

   o Using 1D or 3D textures.

   o Using texture borders.

   o Using glDepthFunc(GL_NEVER).

   o Using the accumulation buffer.

The AGP mode may be set to 1, 2, or 4.  One is used by default.  Higher AGP
speeds may result in unreliable performance depending on your motherboard.

Compaq has funded the implementation of AGP accelerated ReadPixels and Draw-
Pixels in this driver.  With this implementation, on a G400 drawing directly
from AGP memory (exported to the client), throughput of up to 1 GB/sec has
been measured.

Additionally Compaq's funding has produced several new extensions in Mesa,
including one (packed_depth_stencil_MESA) which enables Read/DrawPixels func-
tionality to operate directly on the packed 24/8 depth/stencil buffers of
this hardware.

In order to access this functionality, the application must ensure that all
pixel processing operations are disabled.  There are in addition a fairly
complex set of rules regarding which packing/unpacking modes must be used,
and which data formats are supported, and alignment constraints.  See the
files in lib/GL/mesa/src/drv/mga/DOCS for a summary of these.  The extension
definitions are included in the Mesa 3.4 source distribution.

10.3.4  IRQ Assignment

There have been problems in the past with the MGA driver being very sluggish
when the DRI is enabled (to the point of being unusable.)  This is caused by
the graphics card not having an interrupt assigned to it.  The current DRI
trunk will attempt to detect this condition and bail out gracefully.

The solution to the above problem is to assign an interrupt to your graphics
card.  This is something you must turn on in your system BIOS configuration.
Please consult your system BIOS manual for instructions on how to enable an
interrupt for your graphics card.

10.3.5  MGA HAL lib

MGAHALlib.a is a binary library Matrox has provided for use under Linux to
expose functionality for which they can not provide documentation.  (For
example TV-Out requires MacroVision be enabled on the output.)  This binary
library also sets the pixel/memory clocks to the optimal settings for your
Matrox card.

Currently the MGAHAL library is required for the G450 to work.  You can down-
load this from the driver section on Matrox's website: www.matrox.com/mga

Here modifications to the DRI build instructions which make the mga ddx
driver use the MGAHAL library:

            1.Put the following define in your host.def file
                 #define UseMatroxHal YES
            2. Place mgaHALlib.a in the following directory
                 xc/programs/Xserver/hw/xfree86/drivers/mga/HALlib/

You can use DualHead on the G400/G450 DH cards by creating two device sec-
tions which both point to the same BusID.  For most AGP devices the BusID
will be "PCI:1:0:0".  Configure your screen section as you would normally
configure XFree86 4.x Multihead.  It should be noted that currently the sec-
ond head does not support direct rendering.

10.3.6  Known Problems

None.

10.4  ATI Rage 128

10.4.1  Requirements

A kernel with AGP GART support (such as Linux 2.4.x) is needed.

10.4.2  Configuration

Your XF86Config file's device section must specify the ati device:

             Section "Device"
                 Identifier  "Rage128"
                 VendorName  "ATI"
                 Driver      "ati"
              Option     "AGPMode" "1"
              Option     "UseCCEFor2D" "false"
             EndSection

The Screen section should then reference the Rage 128 device:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "Rage128"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
              Subsection "Display"
               Depth       32
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

The kernel module for the Rage 128 is named r128.o and should be installed in
/lib/modules/2.4.x/kernel/drivers/char/drm/.  It will be automatically loaded
by the Xserver if needed.

The DRI 3D driver for the Rage 128 should be in /usr/X11R6/lib/mod-
ules/dri/r128_dri.so.  This will be automatically loaded by libGL.so.

You may also set your screen depth to 32 for 32bpp mode.

10.4.3  Performance and Features

While PCI Rage 128 based cards are supported, they do not yet support PCI
GART, so they will not perform as well as their AGP counterparts.

For AGP cards, the AGP mode may be set to 1, 2, or 4.  One is used by
default.  Higher AGP speeds may result in unreliable performance depending on
your motherboard.

Note that even at 32bpp there is no alpha channel.

The following OpenGL features are implemented in software and will be slow:

   o accumulation buffer operations

   o stencil, when using a 16bpp screen

   o Blend subtract, min/max and logic op blend modes

   o GL_SEPARATE_SPECULAR_COLOR lighting mode

   o glDrawBuffer(GL_FRONT_AND_BACK)

   o Using 1D or 3D textures

   o Using texture borders

10.4.4  Known Problems

If you experience stability problems you may try setting the UseCCEFor2D
option to true.  This will effectively disable 2D hardware acceleration.
Performance will be degraded, of course.

10.5  ATI Radeon

10.5.1  Requirements

A kernel with AGP GART support (such as Linux 2.4.x) is needed.

10.5.2  Configuration

Your XF86Config file's device section must specify the ati device:

             Section "Device"
                 Identifier  "Radeon"
                 VendorName  "ATI"
                 Driver      "ati"
              Option     "AGPMode" "1"
             EndSection

The Screen section should then reference the Radeon device:

          Section "Screen"
              Identifier  "Screen 1"
              Device      "Radeon"
              Monitor     "High Res Monitor"
              DefaultDepth 16
              Subsection "Display"
               Depth       16
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
              Subsection "Display"
               Depth       32
               Modes       "1280x1024" "1024x768" "800x600" "640x480"
               ViewPort    0 0
              EndSubsection
             EndSection

The kernel module for the Radeon is named radeon.o and should be installed in
/lib/modules/2.4.x/kernel/drivers/char/drm/.  It will be automatically loaded
by the Xserver if needed.

The DRI 3D driver for the Radeon should be in /usr/X11R6/lib/mod-
ules/dri/radeon_dri.so.  This will be automatically loaded by libGL.so.

You may also set your screen depth to 32 for 32bpp mode.

10.5.3  Performance and Features

While this driver supports many of the features of ATI Radeon cards, we do
not yet fully support the card's TCL features.  This work is progressing, but
is not yet ready.

The AGP mode may be set to 1, 2, or 4.  One is used by default.  Higher AGP
speeds may result in unreliable performance depending on your motherboard.

The following OpenGL features are implemented in software and will be slow:

   o Blend subtract, blend min/max and blend logicops

   o Stencil and accumulation operations

   o 1D and 3D textures

   o Texture borders

The GL_EXT_texture_env_combine, GL_EXT_texture_env_add and GL_EXT_tex-
ture_env_dot3 extensions are supported (or will be soon supported in the new
driver based on Mesa 3.5).

We hope to implement support for the following features in the future:

   o Vertex transformation, clipping and lighting (TCL)

   o Hardware stencil buffer

   o Cube map textures

   o 3D textures

   o Three texture units

10.5.4  Known Problems

Certain (early?) revisions of the AMD Irongate chipset have AGPGART problems
which effect Radeon, and other graphics cards.  The card may work unreliably,
or not work at all.  If the DRM kernel module is not loaded, the 2D Xserver
may work.  There's hope that this can be fixed in the future.

10.6  3DLabs Oxygen GMX 2000

The driver for this hardware was experimental and is no longer being devel-
oped or supported.

11.  General Limitations and Known Bugs

11.1  OpenGL

The following OpenGL features are not supported at this time: overlays,
stereo, hardware-accelerated indirect rendering.

OpenGL-like functionality is provided with the Mesa library.  XFree86 4.1.0
uses Mesa 3.4.2.  Subsequent releases of XFree86 will use newer versions of
Mesa.  When newer versions of Mesa are available, the 3D drivers can be
updated without reinstalling XFree86 or libGL.so.

11.2  GLX

The GLX 1.3 API is exported but none of the new 1.3 functions are opera-
tional.

The new glXGetProcAddressARB function is fully supported.

GLXPixmap rendering is only supported for indirect rendering contexts.  This
is a common OpenGL limitation.  Attempting to use a direct rendering context
with a GLXPixmap will result in an X protocol error.

11.3  Debugging

Debugging DRI drivers with gdb can be difficult because of the locking
involved.  When debugging OpenGL applications, you should avoid stepping
inside the GL functions.  If you're trying to debug a DRI driver it's recom-
mended that you do so remotely, from a second system.

11.4  Scheduling

When you run multiple GL applications at once you may notice poor time slic-
ing.  This is due to an interaction problem with the Linux scheduler which
will be addressed in the future.

11.5  libGL.so and dlopen()

A number of popular OpenGL applications on Linux (such as Quake3, HereticII,
Heavy Gear 2, etc) dynamically open the libGL.so library at runtime with
dlopen(), rather than linking with -lGL at compile/link time.

If dynamic loading of libGL.so is not implemented carefully, there can be a
number of serious problems.  Here are the things to be careful of in your
application:

   o Specify the RTLD_GLOBAL flag to dlopen().  If you don't do this then
     you'll likely see a runtime error message complaining that _glapi_Con-
     text is undefined when libGL.so tries to open a hardware-specific
     driver.  Without this flag, nested opening of dynamic libraries does not
     work.

   o Do not close the library with dlclose() until after XCloseDisplay() has
     been called.  When libGL.so initializes itself it registers several
     callbacks functions with Xlib.  When XCloseDisplay() is called those
     callback functions are called.  If libGL.so has already been unloaded
     with dlclose() this will cause a segmentation fault.

   o Your application should link with -lpthread.  On Linux, libGL.so uses
     the pthreads library in order to provide thread safety.  There is appar-
     ently a bug in the dlopen()/dlclose() code which causes crashes if the
     library uses pthreads but the parent application doesn't.  The only
     known work-around is to link the application with -lpthread.

Some applications don't yet incorporate these procedures and may fail.  For
example, changing the graphics settings in some video games will expose this
problem.  The DRI developers are working with game vendors to prevent this
problem in the future.

11.6  Bug Database

The DRI bug database which includes bugs related to specific drivers is at
the SourceForge DRI Bug Database

Please scan both the open and closed bug lists to determine if your problem
has already been reported and perhaps fixed.

12.  Resources

12.1  Software

A collection of useful configuration files, libraries, headers, utilities and
demo programs is available from http://dri.sourceforge.net/res.phtml

12.2  Documentation

   o General OpenGL information is available at the OpenGL Home Page

   o XFree86 information is available at the XFree86 Home Page

   o Information about the design of the DRI is available from Precision
     Insight, Inc.

   o Visit the DRI project on SourceForge.net for the latest development news
     about the DRI and 3D drivers.

   o The DRI Compilation Guide explains how to download, compile and install
     the DRI for yourself.

12.3  Support

   o The DRI-users mailing list at SourceForge is a forum for people to dis-
     cuss DRI problems.

   o In the future there may be IHV and Linux vendor support resources for
     the DRI.

     Generated from XFree86: xc/programs/Xserver/hw/xfree86/doc/sgml/DRI.sgml,v 1.29 dawes Exp $


$XFree86: xc/programs/Xserver/hw/xfree86/doc/README.DRI,v 1.22 2003/07/15 02:28:28 dawes Exp $
