XFree86 4.0 and DRI Users Guide

Brian Paul Precision Insight, Inc.


1. Preamble

1.1 Copyright

Copyright © 2000 by Precision Insight, Inc., Cedar Park, Texas. 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 Interactive, Incorporated. All other trademarks mentioned are the property of their respective owners.

2. Introduction

With XFree86 4.0 and Precision Insight's Direct Rendering Interface (DRI), hardware accelerated 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 4.0; it is assumed that you've already installed a Linux distribution which includes XFree86 4.0.

3. Supported Hardware

3D acceleration is currently only available for systems with Intel-compatible CPUs. Support for Alpha, and perhaps other CPUs, should be available in the future.

XFree86 4.0 includes 3D acceleration for the following graphics hardware:

Support for the following hardware is underway:

4. Prerequisite Software

Mesa 3.3 (beta) is included with XFree86 4.0; there is no need to download the stand-alone Mesa distribution.

5. X Server Start-up

This section describes the steps needed to start the X server with 3D acceleration support.

5.1 Kernel module

Before starting the X server you must install the correct kernel module for your hardware.

This can be done by executing the following as root:

          insmod XXX/drivername.o

For example, on 3dfx hardware, the kernel module is called tdfx.o so you you would type insmod XXX/tdfx.o

Verify that the kernel module was installed by checking that /proc/dri/0 exists.

5.2 XF86Config file

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"

Next, the DRI section can be used to restrict access to direct rendering.

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

        Section "DRI"
             Mode 0666

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:


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

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.]

Next, the Device section of the XF86Config file must describe your particular hardware. For example, here's the Device section for a 3dfx Voodoo3 card:

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

Finally, the Screen section of the XF86Config file may have to be specially configured as well. For example, Voodoo3 hardware acceleration is only available in 16bpp mode.

        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

If there are errors in the XF86Config file, the X server will log errors to the file /var/log/XFree86.0.log

6. Using 3D Acceleration

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

6.1 libGL.so

Your OpenGL program must link with the libGL.so.1.2 library provided by XFree86 4.0. The libGL.so.1.2 library contains a GLX protocol encoder for indirect/remote rendering and DRI code for accessing hardware drivers. In particular, 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 appropriate 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.

6.2 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, libGLU.so and X libraries are located.

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

6.3 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.

6.4 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: Precision Insight, Inc.
          OpenGL renderer string: Mesa DRI Voodoo3 20000224
          OpenGL version string: 1.2 Mesa 3.3 beta

or this:

          OpenGL vendor string: Precision Insight, Inc.
          OpenGL renderer string: Mesa GLX Indirect
          OpenGL version string: 1.2 Mesa 3.3 beta

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. Here you can determine which visuals may have depth buffers, stencil buffers, accumulation buffers, etc.

6.5 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 diagnostic messages. This can help to solve problems.
  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_DIR can be used to override the default directory which is searched for 3D drivers. In a typical XFree86 installation, the 3D drivers should be in /usr/X11R6/lib/modules/dri/. This environment variable can be used to specify a different directory. Note that this feature is disabled for set-uid programs.

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.

7. General Trouble Shooting

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

7.1 Starting 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 and not an older version. If you run xdpyinfo and look for the following line near the top:
                vendor release number:    400
  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:

7.2 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 correctly.

  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.


            % 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.

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

8. Hardware-Specific Information and Troubleshooting

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

8.1 3dfx Voodoo3



Known Problems

8.2 Intel i810

8.3 Matrox G400

8.4 ATI Rage 128

8.5 3DLabs Oxygen GMX 2000

The driver for this hardware is experimental and is missing a lot of features.

9. Limitations and Known Bugs

9.1 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 4.0 uses a beta version Mesa 3.3. When newer versions of Mesa are available, the 3D drivers can be updated without reinstalling XFree86 or libGL.so.

9.2 GLX

The GLX 1.3 API is exported but none of the new 1.3 functions are operational.

The new glXGetProcAddressARB function is fully supported.

9.3 Signal Handling

There are several understood, but unresolved problems relating to hardware locking and signal handling. Hitting CTRL-z to suspend a 3D application can sometimes cause the X server to lock-up if executing device driver code at that moment. Also, using a debugger to step through OpenGL/Mesa device driver functions code could cause a lock-up. These problems will be fixed in the future.

9.4 Scheduling

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

9.5 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.

10. Resources

10.1 Software

A collection of useful configuration files, libraries, headers, utilities and demo programs is available from resources/resources.html

10.2 Documentation

10.3 Support