With hardware 3D acceleration, three-dimensional rendering uses the graphics processor on your video card instead of taking up valuable CPU resources drawing 3D images. It's also referred to as "hardware acceleration" instead of "software acceleration" because without this 3D acceleration your CPU is forced to draw everything itself using the Mesa software rendering libraries, which takes up quite a bit of processing power. While XFree86 typically supports 2D hardware acceleration, it often lacks hardware 3D acceleration. Three-dimensional hardware acceleration is valuable in situations requiring rendering of 3D objects such as games, 3D CAD and modeling.

In many cases, both binary and open-source drivers exist. Open-source drivers are preferable since we're using Linux and open source is one of its underlying principles. Sometimes, binary drivers are the only option, like with nVidia's cards. Binary drivers include media-video/nvidia-kernel and media-video/nvidia-glx for nVidia cards, media-video/mgavideo for Matrox cards and media-video/ati-drivers for ATI cards. Other open-source drivers include media-video/kyro-kernel for KyroII cards and media-video/ati-gatos for ATI cards, which aim to support ATI's video capabilities more fully.

The Direct Rendering Infrastructure (dri.sourceforge.net), also known as the DRI, is a framework for allowing direct access to graphics hardware in a safe and efficient manner. It includes changes to the X server, to several client libraries and to the kernel. The first major use for the DRI is to create fast OpenGL implementations.

XFree-DRM is an enhancement to XFree86 that adds 3D acceleration for cards by adding the kernel module necessary for direct rendering.

This guide is for people who can't get direct rendering working with just XFree. XFree-DRM works for 3dfx, gamma, i8x0, matrox, rage128, radeon, mach64 (as of xfree-drm-4.3.0-r7) and sis300 series drivers. Since the 2.4 kernels' Direct Rendering Manager (DRM) doesn't support XFree 4.3, the xfree-drm package is needed. If you're using a 2.6 kernel, its DRM supports XFree 4.3; Gentoo's XFree-DRM package is not yet working on 2.6 kernels. See the DRI homepage for more info and documentation.

With suggestions, questions, etc., e-mail Donnie Berkholz.

# emerge x11-base/xfree

Probe for your chipset and enable just that one.

# emerge pciutils; lspci | grep AGP
# 00:01.0 PCI bridge: Intel Corp. 440BX/ZX/DX - 82443BX/ZX/DX AGP bridge (rev 03)
Your output may not match the above due to different hardware.

Most, if not all, kernels should have these options. This was configured using gentoo-sources-2.4.20-r5.

# ls -l /usr/src/linux 
lrwxrwxrwx    1 root     root           22 May 29 18:20 /usr/src/linux -> linux-2.4.20-gentoo-r5
Make sure /usr/src/linux links to your current kernel.
# cd /usr/src/linux
# make menuconfig

Processor type and features --->
<*> MTRR (Memory Type Range Register) support
Character devices --->
<*> /dev/agpgart (AGP Support)
[M] Intel 440LX/BX/GX and I815/I820/I830M/I830MP/I840/I845/I850/I860 support
Enable your chipset instead of the above.
[ ] Direct Rendering Manager (XFree86 DRI support)

Make sure the Direct Rendering Manager (DRM) is off. The XFree-DRM package will provide its own. The 2.4 kernel's version is for XFree 4.2.

# make dep && make clean bzImage modules modules_install
# mount /boot
# cp arch/i386/boot/bzImage /boot

If you want your kernel to be named something other than bzImage, be sure to copy to /boot/yourname instead. Don't forget to set up grub.conf or lilo.conf and run /sbin/lilo if you use LILO.

# ACCEPT_KEYWORDS="~x86" emerge xfree-drm

Open /etc/X11/XF86Config with your favorite text editor and edit it to enable DRI and GLX.

...
Section "Module"
  Load "dri"
  Load "glx"
  ...
EndSection
...
Section "Device"
  Driver "radeon"
  ...
EndSection
...
Section "dri"
  Mode 0666
EndSection

If you are using a different driver, replace "radeon" with yours.

Reboot your computer to your new kernel. It's time to see if you have direct rendering and how good it is.

# startx
No need to load modules for your driver or agpgart, if you compiled agpgart as a module.
They will be loaded automatically.
# glxinfo | grep rendering
direct rendering: Yes
If it says "No," you don't have 3D acceleration.
# glxgears
Test your frames per second (FPS) at the default size. The number should be 
significantly higher than before installing xfree-drm. Do this while the CPU is as idle as possible.

First you have to check whether the xfree-drm package works. If it doesn't and you have checked your logs to verify it's not a configuration error, you might want to consider the CVS sources. There are also daily driver snapshots available if you do not wish to build the full CVS.

Check the DRI supported cards list to see if the CVS supports your card. Even if it doesn't, but it supports a similar card, try it.

Follow this guide through "Compile and install your kernel." Then continue with this guide, which tracks step 6 of the DRI compilation guide and follows it through step 8.3.

Create a directory to store the CVS files:

# cd ~
# mkdir DRI-CVS

Check out the CVS sources:

# cd ~/DRI-CVS
# cvs -d:pserver:anonymous@cvs.dri.sourceforge.net:/cvsroot/dri login
(hit ENTER when prompted for a password)
# cvs -z3 -d:pserver:anonymous@cvs.dri.sourceforge.net:/cvsroot/dri co xc
The -z3 flag causes compression to be used to reduce the download time.

In the future you'll want to occasionally update your local copy of the DRI source code to get the latest changes. This can be done with:

# cd ~/DRI-CVS
# cvs -z3 update -dA xc
The -d flag causes any new subdirectories to be created.
The -A flag causes most recent trunk sources to be fetched, not branch sources.

Rather than placing object files and library files right in the source tree, they're instead put into a parallel build tree. The build tree is made with the lndir command:

# cd ~/DRI-CVS
# ln -s xc XFree40
# mkdir build; cd build
# lndir -silent -ignorelinks ../XFree40

The build tree will be populated with symbolic links which point back into the CVS source tree. Advanced users may have several build trees for compiling and testing with different options.

The ~/DRI-CVS/build/xc/config/cf/host.def file is used to configure the XFree86 build process. You can change it to customize your build options or make adjustments for your particular system configuration. The default host.def file will look something like this:

#define DefaultCCOptions -Wall
For i386:
#define DefaultGcc2i386Opt -O2
For Alpha:
#define DefaultGcc2AxpOpt -O2 -mcpu=ev6 (or similar)
For all architectures
#define LibraryCDebugFlags -O2
#define BuildServersOnly YES
#define XF86CardDrivers vga tdfx mga ati i810
#define LinuxDistribution LinuxRedHat
#define DefaultCCOptions -ansi GccWarningOptions -pipe
#define BuildXF86DRI YES
/* Optionally turn these on for debugging */
/* #define GlxBuiltInTdfx YES */
/* #define GlxBuiltInMga YES */
/* #define GlxBuiltInR128 YES */
/* #define GlxBuiltInRadeon YES */
/* #define DoLoadableServer NO */
#define SharedLibFont NO

Note the XF86CardDrivers line to be sure your card's driver is listed.
If you want to enable 3DNow! optimizations in Mesa and the DRI drivers, you should add the following:
#define MesaUse3DNow YES
You don't have to be using an AMD processor to enable this option.
The DRI will look for 3DNow! support at runtime and only enable it if applicable.

If you want to enable SSE optimizations in Mesa and the DRI drivers, you must upgrade to a Linux 2.4.x kernel. Mesa will verify that SSE is supported by both your processor and your operating system, but to build Mesa inside the DRI you need to have the Linux 2.4.x kernel headers in /usr/src/linux. If you enable SSE optimizations with an earlier version of the Linux kernel in /usr/src/linux, Mesa will not compile. You have been warned. If you do have a 2.4.x kernel, you should add the following:

#define MesaUseKatmai YES

To compile the complete DRI tree:

# cd ~/DRI-CVS/build/xc/
# make World >& world.log

It may also be necessary to do the following, depending on what you placed in host.def:

# cd ~/DRI-CVS/build/xc/programs/Xserver/hw/xfree86/os-support/linux/drm/kernel
# make -f Makefile.linux radeon.o
Replace radeon with your driver.

With the default compilation flags it's normal to get a lot of warnings during compilation. Building will take some time so you may want to go check your email or visit slashdot.

Using your text editor, examine world.log for errors by searching for the pattern ***.

Verify that the DRI kernel module(s) for your system were built:

# cd ~/DRI-CVS/build/xc/programs/Xserver/hw/xfree86/os-support/linux/drm/kernel; ls

For the 3dfx Voodoo, you should see tdfx.o. For the Matrox G200/G400, you should see mga.o. For the ATI Rage 128, you should see r128.o. For the ATI Radeon, you should see radeon.o. For the Intel i810, you should see i810.o. If the DRI kernel module(s) failed to build, you should verify that you're using the right version of the Linux kernel. The most recent kernels are not always supported.

Install over your XFree86 installation. You may wish to back up xfree.

# quickpkg xfree
This backs up your XFree86 package.
# make install

Follow the "Configure XF86Config" section above.

To load the appropriate DRM module in your running kernel, copy the kernel module to /lib/modules/`uname -r`/kernel/drivers/char/drm/ then run modules-update and restart your X server. If you're not running the kernel you'll be using it in, instead of `uname -r`, use that kernel's name.

A few options may increase performance by up to 30 percent (or more) over the default. Set them in /etc/X11/XF86Config.

Section "Device"
  Option     "AGPMode" "4"
  This increased FPS from 609 to 618.
  Option     "AGPFastWrite" "True"
  This had no measurable effect, but it may increase instability of your computer.
  You may also need to set it in your BIOS.
  Option     "EnablePageFlip" "True"
  This improved FPS from 618 to 702. It also is "risky" but few people have reported problems.
  ...
EndSection

If you want to set even more features, check out the features listing on the DRI Web site.

Whenever you rebuild your kernel or switch to another kernel, you'll have to rebuild the kernel module. Note that you don't need to remerge xfree, but you will need to remerge xfree-drm.

Try insmod radeon before you start the X server. Also, try building agpgart into the kernel instead of as a module.

That's because you compiled agpgart into the kernel instead of as a module. Ignore it unless you're having problems.

You aren't using the xfree-drm driver. Check if you compiled DRM and the driver into the kernel; you shouldn't have.

Check out ati-gatos drivers. emerge -s gatos.

Try out the binary drivers. For ati-drivers, a listing is at http://www.schneider-digital.de/html/download_ati.html. If those don't support it, use fbdev. It's slow, but it works.

In section "Device" enable ForcePCIMode.

Option "ForcePCIMode" "True"

1. Christopher Webber for suggesting a troubleshooting question about changing or recompiling kernels
2. Steve, for suggesting consistency between the cases of dri and DRI in XF86Config

1. http://forums.gentoo.org/viewtopic.php?t=46681
2. http://forums.gentoo.org/viewtopic.php?t=29264
3. http://dri.sourceforge.net/
4. http://www.retinalburn.net/linux/dri_status.html