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<h1>The Mesa 3D Graphics Library</h1> |
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<h1>Mesa Frequently Asked Questions</h1> |
Last updated: 9 October 2012 |
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<h2>Index</h2> |
<a href="#part1">1. High-level Questions and Answers</a> |
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<a href="#part2">2. Compilation and Installation Problems</a> |
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<a href="#part3">3. Runtime / Rendering Problems</a> |
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<a href="#part4">4. Developer Questions</a> |
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<h1 id="part1">1. High-level Questions and Answers</h1> |
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<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 9.x supports the OpenGL 3.1 specification. |
</p> |
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<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 X.org. |
</p> |
<ul> |
<li>See the <a href="http://dri.freedesktop.org/">DRI website</a> |
for more information.</li> |
<li>See <a href="http://intellinuxgraphics.org">intellinuxgraphics.org</a> |
for more information about Intel drivers.</li> |
<li>See <a href="http://nouveau.freedesktop.org">nouveau.freedesktop.org</a> |
for more information about Nouveau drivers.</li> |
<li>See <a href="http://www.x.org/wiki/RadeonFeature">www.x.org/wiki/RadeonFeature</a> |
for more information about Radeon drivers.</li> |
</ul> |
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<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 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> |
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<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> |
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<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> |
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<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"> |
OpenGL Sample Implementation (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> |
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<p> |
<a href="http://sourceforge.net/projects/ogl-es/">Vincent</a> is |
an open-source implementation of OpenGL ES for mobile devices. |
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<p> |
<a href="http://www.dsbox.com/minigl.html">miniGL</a> |
is a subset of OpenGL for PalmOS devices. |
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<p> |
<a href="http://bellard.org/TinyGL/">TinyGL</a> |
is a subset of OpenGL. |
</p> |
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<p> |
<a href="http://sourceforge.net/projects/softgl/">SoftGL</a> |
is an OpenGL subset for mobile devices. |
</p> |
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<p> |
<a href="http://chromium.sourceforge.net/">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> |
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<p> |
<a href="http://www.ticalc.org/archives/files/fileinfo/361/36173.html">ClosedGL</a> |
is an OpenGL subset library for TI graphing calculators. |
</p> |
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<p> |
There may be other open OpenGL implementations, but Mesa is the most |
popular and feature-complete. |
</p> |
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<h1 id="part2">2. Compilation and Installation Problems</h1> |
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<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> |
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<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> |
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<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> |
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<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> |
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<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">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> |
When configuring Mesa, there are three autoconf options that affect the install |
location that you should take care with: <code>--prefix</code>, |
<code>--libdir</code>, and <code>--with-dri-driverdir</code>. To install Mesa |
into the system location where it will be available for all programs to use, set |
<code>--prefix=/usr</code>. Set <code>--libdir</code> to where your Linux |
distribution installs system libraries, usually either <code>/usr/lib</code> or |
<code>/usr/lib64</code>. Set <code>--with-dri-driverdir</code> to the directory |
where your Linux distribution installs DRI drivers. To find your system's DRI |
driver directory, try executing <code>find /usr -type d -name dri</code>. For |
example, if the <code>find</code> command listed <code>/usr/lib64/dri</code>, |
then set <code>--with-dri-driverdir=/usr/lib64/dri</code>. |
</p> |
<p> |
After determining the correct values for the install location, configure Mesa |
with <code>./configure --prefix=/usr --libdir=xxx --with-dri-driverdir=xxx</code> |
and then install with <code>sudo make install</code>. |
</p> |
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<h1 id="part3">3. Runtime / Rendering Problems</h1> |
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<h2>3.1 Rendering is slow / why isn't my graphics hardware being used?</h2> |
<p> |
If Mesa can't use its hardware accelerated drivers it falls back on one of its software renderers. |
(eg. classic swrast, softpipe or llvmpipe) |
</p> |
<p> |
You can run the <code>glxinfo</code> program to learn about your OpenGL |
library. |
Look for the <code>OpenGL vendor</code> and <code>OpenGL renderer</code> values. |
That will identify who's OpenGL library with which driver you're using and what sort of |
hardware it has detected. |
</p> |
<p> |
If you're using a hardware accelerated driver you want <code>direct rendering: Yes</code>. |
</p> |
<p> |
If your DRI-based driver isn't working, go to the |
<a href="http://dri.freedesktop.org/">DRI website</a> for trouble-shooting information. |
</p> |
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<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">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> |
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<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> |
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<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> |
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<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> |
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<h1 id="part4">4. Developer Questions</h1> |
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<h2>4.1 How can I contribute?</h2> |
<p> |
First, join the <a href="lists.html">mesa-dev mailing list</a>. |
That's where Mesa development is discussed. |
</p> |
<p> |
The <a href="http://www.opengl.org/documentation"> |
OpenGL Specification</a> is the bible for OpenGL implementation 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> |
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<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 classic hardware driver, the i965 driver is a good example. |
For a Gallium3D hardware driver, the r300g, r600g and the i915g 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 seldom 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> |
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<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">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 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). |
</p> |
<p> |
In the mean time, a 3rd party <a href="http://dri.freedesktop.org/wiki/S3TC"> |
plug-in library</a> is available. |
</p> |
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