The Mesa 3D Graphics Library

Mesa Frequently Asked Questions

Last updated: 9 October 2012


Index

1. High-level Questions and Answers
2. Compilation and Installation Problems
3. Runtime / Rendering Problems
4. Developer Questions


1. High-level Questions and Answers

1.1 What is Mesa?

Mesa is an open-source implementation of the OpenGL specification. OpenGL is a programming library for writing interactive 3D applications. See the OpenGL website for more information.

Mesa 9.x supports the OpenGL 3.1 specification.

1.2 Does Mesa support/use graphics hardware?

Yes. Specifically, Mesa serves as the OpenGL core for the open-source DRI drivers for X.org.

1.3 What purpose does Mesa serve today?

Hardware-accelerated OpenGL implementations are available for most popular operating systems today. Still, Mesa serves at least these purposes:

1.4 What's the difference between "Stand-Alone" Mesa and the DRI drivers?

Stand-alone Mesa is the original incarnation of Mesa. On systems running the X Window System it does all its rendering through the Xlib API:

Alternately, Mesa acts as the core for a number of OpenGL hardware drivers within the DRI (Direct Rendering Infrastructure):

1.5 How do I upgrade my DRI installation to use a new Mesa release?

This wasn't easy in the past. Now, the DRI drivers are included in the Mesa tree and can be compiled separately from the X server. Just follow the Mesa compilation instructions.

1.6 Are there other open-source implementations of OpenGL?

Yes, SGI's OpenGL Sample Implementation (SI) is available. The SI was written during the time that OpenGL was originally designed. Unfortunately, development of the SI has stagnated. Mesa is much more up to date with modern features and extensions.

Vincent is an open-source implementation of OpenGL ES for mobile devices.

miniGL is a subset of OpenGL for PalmOS devices.

TinyGL is a subset of OpenGL.

SoftGL is an OpenGL subset for mobile devices.

Chromium isn't a conventional OpenGL implementation (it's layered upon OpenGL), but it does export the OpenGL API. It allows tiled rendering, sort-last rendering, etc.

ClosedGL is an OpenGL subset library for TI graphing calculators.

There may be other open OpenGL implementations, but Mesa is the most popular and feature-complete.



2. Compilation and Installation Problems

2.1 What's the easiest way to install Mesa?

If you're using a Linux-based system, your distro CD most likely already has Mesa packages (like RPM or DEB) which you can easily install.

2.2 I get undefined symbols such as bgnpolygon, v3f, etc...

You're application is written in IRIS GL, not OpenGL. IRIS GL was the predecessor to OpenGL and is a different thing (almost) entirely. Mesa's not the solution.

2.3 Where is the GLUT library?

GLUT (OpenGL Utility Toolkit) is no longer in the separate MesaGLUT-x.y.z.tar.gz file. If you don't already have GLUT installed, you should grab freeglut.

2.4 Where is the GLw library?

GLw (OpenGL widget library) is now available from a separate git repository. Unless you're using very old Xt/Motif applications with OpenGL, you shouldn't need it.

2.5 What's the proper place for the libraries and headers?

On Linux-based systems you'll want to follow the Linux ABI standard. Basically you'll want the following:

When configuring Mesa, there are three autoconf options that affect the install location that you should take care with: --prefix, --libdir, and --with-dri-driverdir. To install Mesa into the system location where it will be available for all programs to use, set --prefix=/usr. Set --libdir to where your Linux distribution installs system libraries, usually either /usr/lib or /usr/lib64. Set --with-dri-driverdir to the directory where your Linux distribution installs DRI drivers. To find your system's DRI driver directory, try executing find /usr -type d -name dri. For example, if the find command listed /usr/lib64/dri, then set --with-dri-driverdir=/usr/lib64/dri.

After determining the correct values for the install location, configure Mesa with ./configure --prefix=/usr --libdir=xxx --with-dri-driverdir=xxx and then install with sudo make install.



3. Runtime / Rendering Problems

3.1 Rendering is slow / why isn't my graphics hardware being used?

If Mesa can't use its hardware accelerated drivers it falls back on one of its software renderers. (eg. classic swrast, softpipe or llvmpipe)

You can run the glxinfo program to learn about your OpenGL library. Look for the OpenGL vendor and OpenGL renderer values. That will identify who's OpenGL library with which driver you're using and what sort of hardware it has detected.

If you're using a hardware accelerated driver you want direct rendering: Yes.

If your DRI-based driver isn't working, go to the DRI website for trouble-shooting information.

3.2 I'm seeing errors in depth (Z) buffering. Why?

Make sure the ratio of the far to near clipping planes isn't too great. Look here for details.

Mesa uses a 16-bit depth buffer by default which is smaller and faster to clear than a 32-bit buffer but not as accurate. If you need a deeper you can modify the parameters to glXChooseVisual in your code.

3.3 Why Isn't depth buffering working at all?

Be sure you're requesting a depth buffered-visual. If you set the MESA_DEBUG environment variable it will warn you about trying to enable depth testing when you don't have a depth buffer.

Specifically, make sure glutInitDisplayMode is being called with GLUT_DEPTH or glXChooseVisual is being called with a non-zero value for GLX_DEPTH_SIZE.

This discussion applies to stencil buffers, accumulation buffers and alpha channels too.

3.4 Why does glGetString() always return NULL?

Be sure you have an active/current OpenGL rendering context before calling glGetString.

3.5 GL_POINTS and GL_LINES don't touch the right pixels

If you're trying to draw a filled region by using GL_POINTS or GL_LINES and seeing holes or gaps it's because of a float-to-int rounding problem. But this is not a bug. See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips". Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates will fix the problem.

3.6 How can I change the maximum framebuffer size in Mesa's swrast backend?

These can be overridden by using the --with-max-width and --with-max-height options. The two need not be equal.

Do note that Mesa uses these values to size some internal buffers, so increasing these sizes will cause Mesa to require additional memory. Furthermore, increasing these limits beyond 4096 may introduce rasterization artifacts; see the leading comments in src/mesa/swrast/s_tritemp.h.



4. Developer Questions

4.1 How can I contribute?

First, join the mesa-dev mailing list. That's where Mesa development is discussed.

The OpenGL Specification is the bible for OpenGL implementation work. You should read it.

Most of the Mesa development work involves implementing new OpenGL extensions, writing hardware drivers (for the DRI), and code optimization.

4.2 How do I write a new device driver?

Unfortunately, writing a device driver isn't easy. It requires detailed understanding of OpenGL, the Mesa code, and your target hardware/operating system. 3D graphics are not simple.

The best way to get started is to use an existing driver as your starting point. For a classic hardware driver, the i965 driver is a good example. For a Gallium3D hardware driver, the r300g, r600g and the i915g are good examples.

The DRI website has more information about writing hardware drivers. The process isn't well document because the Mesa driver interface changes over time, and we seldom have spare time for writing documentation. That being said, many people have managed to figure out the process.

Joining the appropriate mailing lists and asking questions (and searching the archives) is a good way to get information.

4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa?

The specification for the extension indicates that there are intellectual property (IP) and/or patent issues to be dealt with.

We've been unsuccessful in getting a response from S3 (or whoever owns the IP nowadays) to indicate whether or not an open source project can implement the extension (specifically the compression/decompression algorithms).

In the mean time, a 3rd party plug-in library is available.