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<h1>Mesa Frequently Asked Questions</h1>
Last updated: 21 August 2006
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<br>
<br>
<h2>Index</h2>
<a href="#part1">1. High-level Questions and Answers</a>
<br>
<a href="#part2">2. Compilation and Installation Problems</a>
<br>
<a href="#part3">3. Runtime / Rendering Problems</a>
<br>
<a href="#part4">4. Developer Questions</a>
<br>
<br>
<br>


<h1 id="part1">1. High-level Questions and Answers</h1>

<h2>1.1 What is Mesa?</h2>
<p>
Mesa is an open-source implementation of the OpenGL specification.
OpenGL is a programming library for writing interactive 3D applications.
See the <a href="http://www.opengl.org/">OpenGL website</a> for more
information.
</p>
<p>
Mesa 6.x supports the OpenGL 1.5 specification.
</p>


<h2>1.2 Does Mesa support/use graphics hardware?</h2>
<p>
Yes.  Specifically, Mesa serves as the OpenGL core for the open-source DRI
drivers for XFree86/X.org.  See the <a href="http://dri.freedesktop.org/">DRI
website</a> for more information.
</p>
<p>
There have been other hardware drivers for Mesa over the years (such as
the 3Dfx Glide/Voodoo driver, an old S3 driver, etc) but the DRI drivers
are the modern ones.
</p>

<h2>1.3 What purpose does Mesa serve today?</h2>
<p>
Hardware-accelerated OpenGL implementations are available for most popular
operating systems today.
Still, Mesa serves at least these purposes:
</p>
<ul>
<li>Mesa is used as the core of the open-source XFree86/X.org DRI
    hardware drivers.
</li>
<li>Mesa is quite portable and allows OpenGL to be used on systems
    that have no other OpenGL solution.
</li>
<li>Software rendering with Mesa serves as a reference for validating the
    hardware drivers.
</li>
<li>A software implementation of OpenGL is useful for experimentation,
    such as testing new rendering techniques.
</li>
<li>Mesa can render images with deep color channels: 16-bit integer
    and 32-bit floating point color channels are supported.
    This capability is only now appearing in hardware.
</li>
<li>Mesa's internal limits (max lights, clip planes, texture size, etc) can be
    changed for special needs (hardware limits are hard to overcome).
</li>
</ul>


<h2>1.4 What's the difference between"Stand-Alone" Mesa and the DRI drivers?</h2>
<p>
<em>Stand-alone Mesa</em> is the original incarnation of Mesa.
On systems running the X Window System it does all its rendering through
the Xlib API:
</p>
<ul>
<li>The GLX API is supported, but it's really just an emulation of the
     real thing.
<li>The GLX wire protocol is not supported and there's no OpenGL extension
    loaded by the X server.
<li>There is no hardware acceleration.
<li>The OpenGL library, libGL.so, contains everything (the programming API,
    the GLX functions and all the rendering code).
</ul>
<p>
Alternately, Mesa acts as the core for a number of OpenGL hardware drivers
within the DRI (Direct Rendering Infrastructure):
<ul>
<li>The libGL.so library provides the GL and GLX API functions, a GLX
    protocol encoder, and a device driver loader.
<li>The device driver modules (such as r200_dri.so) contain a built-in
    copy of the core Mesa code.
<li>The X server loads the GLX module.
    The GLX module decodes incoming GLX protocol and dispatches the commands
    to a rendering module.
    For the DRI, this module is basically a software Mesa renderer.
</ul>


<h2>1.5 How do I upgrade my DRI installation to use a new Mesa release?</h2>
<p>
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 <a href="install.html">compilation instructions</a>.
</p>


<h2>1.6 Are there other open-source implementations of OpenGL?</h2>
<p>
Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html"
target="_parent">
OpenGL Sample Implemenation (SI)</a> 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.
</p>

<p>
<a href="http://ogl-es.sourceforge.net" target="_parent">Vincent</a> is
an open-source implementation of OpenGL ES for mobile devices.

<p>
<a href="http://www.dsbox.com/minigl.html" target="_parent">miniGL</a>
is a subset of OpenGL for PalmOS devices.

<p>
<a href="http://fabrice.bellard.free.fr/TinyGL/"
target="_parent">TinyGL</a> is a subset of OpenGL.
</p>

<p>
<a href="http://softgl.studierstube.org/" target="_parent">SoftGL</a>
is an OpenGL subset for mobile devices.
</p>

<p>
<a href="http://chromium.sourceforge.net/" target="_parent">Chromium</a>
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.
</p>

<p>
<a href="http://www.ticalc.org/archives/files/fileinfo/361/36173.html"
target="_parent">ClosedGL</a> is an OpenGL subset library for TI
graphing calculators.
</p>

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


<br>
<br>


<h1 id="part2">2. Compilation and Installation Problems</h1>


<h2>2.1 What's the easiest way to install Mesa?</h2>
<p>
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.
</p>


<h2>2.2 I get undefined symbols such as bgnpolygon, v3f, etc...</h2>
<p>
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.
</p>


<h2>2.3 Where is the GLUT library?</h2>
<p>
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
<a href="http://freeglut.sourceforge.net/">freeglut</a>.
</p>


<h2>2.4 Where is the GLw library?</h2>
<p>
GLw (OpenGL widget library) is now available from a separate <a href="http://cgit.freedesktop.org/mesa/glw/">git repository</a>.  Unless you're using very old Xt/Motif applications with OpenGL, you shouldn't need it.
</p>


<h2>2.5 What's the proper place for the libraries and headers?</h2>
<p>
On Linux-based systems you'll want to follow the
<a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html"
target="_parent">Linux ABI</a> standard.
Basically you'll want the following:
</p>
<ul>
<li>/usr/include/GL/gl.h - the main OpenGL header
</li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
</li><li>/usr/include/GL/glx.h - the OpenGL GLX header
</li><li>/usr/include/GL/glext.h - the OpenGL extensions header
</li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
</li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
</li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
</li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
</li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library.  xyz denotes the
Mesa version number.
</li></ul>
<p>
After installing XFree86/X.org and the DRI drivers, some of these files
may be symlinks into the /usr/X11R6/ tree.
</p>
<p>
The old-style Makefile system doesn't install the Mesa libraries; it's
up to you to copy them (and the headers) to the right place.
</p>
<p>
The GLUT header and library should go in the same directories.
</p>
<br>
<br>


<h1 id="part3">3. Runtime / Rendering Problems</h1>

<h2>3.1 Rendering is slow / why isn't my graphics hardware being used?</h2>
<p>
Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any
support for hardware acceleration (with the exception of the 3DFX Voodoo
driver).
</p>
<p>
What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
for your particular hardware.
</p>
<p>
You can run the <code>glxinfo</code> program to learn about your OpenGL
library.
Look for the GL_VENDOR and GL_RENDERER values.
That will identify who's OpenGL library you're using and what sort of
hardware it has detected.
</p>
<p>
If your DRI-based driver isn't working, go to the
<a href="http://dri.sf.net/" target="_parent">DRI website</a> for trouble-shooting information.
</p>


<h2>3.2 I'm seeing errors in depth (Z) buffering.  Why?</h2>
<p>
Make sure the ratio of the far to near clipping planes isn't too great.
Look
<a href="http://www.opengl.org/resources/faq/technical/depthbuffer.htm#0040"
target="_parent"> here</a> for details.
</p>
<p>
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
<code> glXChooseVisual</code> in your code.
</p>


<h2>3.3 Why Isn't depth buffering working at all?</h2>
<p>
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.
</p>
<p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
called with a non-zero value for GLX_DEPTH_SIZE.
</p>
<p>This discussion applies to stencil buffers, accumulation buffers and
alpha channels too.
</p>


<h2>3.4 Why does glGetString() always return NULL?</h2>
<p>
Be sure you have an active/current OpenGL rendering context before
calling glGetString.
</p>


<h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
<p>
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.
</p>

<h2>3.6 How can I change the maximum framebuffer size in Mesa's
<tt>swrast</tt> backend?</h2>
<p>
These can be overridden by using the <tt>--with-max-width</tt> and
<tt>--with-max-height</tt> options.  The two need not be equal.
</p><p>
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 <tt>4096</tt>
may introduce rasterization artifacts; see the leading comments in
<tt>src/mesa/swrast/s_tritemp.h</tt>.
</p>

<br>
<br>


<h1 id="part4">4. Developer Questions</h1>

<h2>4.1 How can I contribute?</h2>
<p>
First, join the <a href="http://www.mesa3d.org/lists.html">Mesa3d-dev
mailing list</a>.
That's where Mesa development is discussed.
</p>
<p>
The <a href="http://www.opengl.org/documentation" target="_parent">
OpenGL Specification</a> is the bible for OpenGL implemention work.
You should read it.
</p>
<p>Most of the Mesa development work involves implementing new OpenGL
extensions, writing hardware drivers (for the DRI), and code optimization.
</p>

<h2>4.2 How do I write a new device driver?</h2>
<p>
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.
</p>
<p>
The best way to get started is to use an existing driver as your starting
point.
For a software driver, the X11 and OSMesa drivers are good examples.
For a hardware driver, the Radeon and R200 DRI drivers are good examples.
</p>
<p>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 seldome have spare time for writing documentation.
That being said, many people have managed to figure out the process.
</p>
<p>
Joining the appropriate mailing lists and asking questions (and searching
the archives) is a good way to get information.
</p>


<h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa?</h2>
<p>
The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a>
indicates that there are intellectual property (IP) and/or patent issues
to be dealt with.
</p>
<p>We've been unsucessful 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).
</p>
<p>
In the mean time, a 3rd party <a href=
"http://dri.freedesktop.org/wiki/S3TC"
target="_parent">plug-in library</a> is available.
</p>

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