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HTML
344 lines
11 KiB
HTML
<html>
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<head><title>Mesa FAQ</title></head>
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<BODY text="#000000" bgcolor="#55bbff" link="#111188">
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<center>
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<h1>Mesa Frequently Asked Questions</h1>
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Last updated: 6 August 2003
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</center>
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<br>
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<br>
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<h2>Index</h2>
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<a href="#part1">1. High-level Questions and Answers</a>
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<br>
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<a href="#part2">2. Compilation and Installation Problems</a>
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<br>
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<a href="#part3">3. Runtime / Rendering Problems</a>
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<br>
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<a href="#part4">4. Developer Questions</a>
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<br>
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<br>
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<br>
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<a name="part1">
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</a><h1><a name="part1">1. High-level Questions and Answers</a></h1>
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<h2><a name="part1">1.1 What is Mesa?</a></h2>
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<p>
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<a name="part1">Mesa is an open-source implementation of the OpenGL specification.
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OpenGL is a programming library for writing interactive 3D applications.
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See the </a><a href="http://www.opengl.org/">OpenGL website</a> for more
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information.
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</p>
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<p>
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Mesa 5.x supports the OpenGL 1.4 specification.
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</p>
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<h2>1.2 Does Mesa support/use graphics hardware?</h2>
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<p>
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Yes. Specifically, Mesa serves as the OpenGL core for the open-source
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XFree86/DRI OpenGL drivers. See the <a href="http://dri.sf.net/">DRI
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website</a> for more information.
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</p>
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<p>
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There have been other hardware drivers for Mesa over the years (such as
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the 3Dfx Glide/Voodoo driver, an old S3 driver, etc) but the DRI drivers
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are the modern ones.
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</p>
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<h2>1.3 What purpose does Mesa (software-based rendering) serve today?</h2>
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<p>
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Hardware-accelerated OpenGL implementations are available for most popular
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operating systems today.
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Still, Mesa serves at least these purposes:
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</p>
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<ul>
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<li>Mesa is used as the core of the open-source XFree86/DRI hardware drivers.
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</li>
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<li>Mesa is quite portable and allows OpenGL to be used on systems
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that have no other OpenGL solution.
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</li>
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<li>Software rendering with Mesa serves as a reference for validating the
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hardware drivers.
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</li>
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<li>A software implementation of OpenGL is useful for experimentation,
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such as testing new rendering techniques.
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</li>
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<li>Mesa can render images with deep color channels: 16-bit integer
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and 32-bit floating point color channels are supported.
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This capability is only now appearing in hardware.
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</li>
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<li>Mesa's internal limits (max lights, clip planes, texture size, etc) can be
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changed for special needs (hardware limits are hard to overcome).
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</li>
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</ul>
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<h2>1.4 How do I upgrade my DRI installation to use a new Mesa release?</h2>
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<p>
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You don't! A copy of the Mesa source code lives inside the XFree86/DRI source
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tree and gets compiled into the individual DRI driver modules.
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If you try to install Mesa over an XFree86/DRI installation, you'll lose
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hardware rendering (because stand-alone Mesa's libGL.so is different than
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the XFree86 libGL.so).
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</p>
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<p>
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The DRI developers will incorporate the latest release of Mesa into the
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DRI drivers when the time is right.
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</p>
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<p>
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To upgrade, either look for a new release of <a href="http://www.xfree86.org"
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target="_parent">XFree86</a> or visit the
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<a href="http://dri.sf.net" target="_parent">DRI website</a> to see
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if there's newer drivers.
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</p>
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<h2>1.5 Are there other open-source implementations of OpenGL?</h2>
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<p>
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Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html">
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OpenGL Sample Implemenation (SI)</a> is available.
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The SI was written during the time that OpenGL was originally designed.
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Unfortunately, development of the SI has stagnated.
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Mesa is much more up to date with modern features and extensions.
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</p>
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<p>
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<a href="http://www.dsbox.com/minigl.html">miniGL</a> is a subset of OpenGL
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for PalmOS devices.
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<a href="http://fabrice.bellard.free.fr/TinyGL/">TinyGL</a> is another
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subset of OpenGL.
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</p>
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<p>
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There may be others but Mesa is the most popular and feature-complete.
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</p>
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<br>
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<br>
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<a name="part2">
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</a><h1><a name="part2">2. Compilation and Installation Problems</a></h1>
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<h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2>
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<p>
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<a name="part2">If you're using a Linux-based system, your distro CD most likely already
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has Mesa packages (like RPM or DEB) which you can easily install.
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</a></p>
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<h2><a name="part2">2.2 Running <code>configure; make</code> Doesn't Work</a></h2>
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<p>
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<a name="part2">Unfortunately, the GNU autoconf/automake/libtool system doesn't seem to work
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too well on non GNU/Linux systems, even after installing gmake, gcc, etc.
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For that reason, Mesa's <b>old-style</b> makefile system is still included.
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The old-style system uses good old traditional Makefiles. Try the following:
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</a></p><pre><a name="part2"> cd Mesa-x.y.z
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cp Makefile.X11 Makefile
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make
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</a></pre>
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<a name="part2">You'll see a list of system configurations from which to choose.
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For example:
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</a><pre><a name="part2"> make linux-x86
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</a></pre>
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<p>
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<a name="part2">If you're experienced with GNU autoconf/automake/libtool and think you can help
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with maintence, contact the Mesa developers.
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FYI, the Mesa developers generally don't use the autoconf/automake system.
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We're especially annoyed with the fact that a +5000-line script (libtool)
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is needed to make shared libraries (ugh).
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</a></p>
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<h2><a name="part2">2.3 Mesa still doesn't compile</a></h2>
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<p>
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<a name="part2">If the old-style Makefile system doesn't work either, make sure you have
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the most recent version of Mesa.
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Otherwise, file a bug report or post to the Mesa3d-users mailing list.
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Give as much info as possible when describing your problem.
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</a></p>
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<h2><a name="part2">2.4 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2>
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<p>
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<a name="part2">You're application is written in IRIS GL, not OpenGL.
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IRIS GL was the predecessor to OpenGL and is a different thing (almost)
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entirely.
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Mesa's not the solution.
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</a></p>
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<h2><a name="part2">2.5 Where is the GLUT library?</a></h2>
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<p>
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<a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaDemos-x.y.z.tar.gz file.
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If you don't already have GLUT installed, you should grab the MesaDemos
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package and unpack it before compiling Mesa.
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</a></p>
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<h2><a name="part2">2.6 What's the proper place for the libraries and headers?</a></h2>
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<p>
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<a name="part2">On Linux-based systems you'll want to follow the
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</a><a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html">Linux ABI</a>
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standard.
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Basically you'll want the following:
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</p>
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<ul>
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<li>/usr/include/GL/gl.h - the main OpenGL header
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</li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
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</li><li>/usr/include/GL/glx.h - the OpenGL GLX header
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</li><li>/usr/include/GL/glext.h - the OpenGL extensions header
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</li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
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</li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
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</li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
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</li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
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</li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library. xyz denotes the
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Mesa version number.
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</li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1
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</li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz
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</li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library. xyz denotes the Mesa
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version number.
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</li></ul>
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<p>
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After installing XFree86 and the DRI drivers, some of these files
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may be symlinks into the /usr/X11R6/ tree.
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</p>
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<p>
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The old-style Makefile system doesn't install the Mesa libraries; it's
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up to you to copy them (and the headers) to the right place.
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</p>
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<p>
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The GLUT header and library should go in the same directories.
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</p>
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<br>
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<br>
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<a name="part3">
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</a><h1><a name="part3">3. Runtime / Rendering Problems</a></h1>
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<h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2>
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<p>
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<a name="part3">Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any
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support for hardware acceleration (with the exception of the 3DFX Voodoo
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driver).
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</a></p>
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<p>
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<a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
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for your particular hardware.
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</a></p>
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<p>
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<a name="part3">You can run the <code>glxinfo</code> program to learn about your OpenGL
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library.
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Look for the GL_VENDOR and GL_RENDERER values.
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That will identify who's OpenGL library you're using and what sort of
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hardware it has detected.
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</a></p>
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<p>
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<a name="part3">If your DRI-based driver isn't working, go to the
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</a><a href="http://dri.sf.net/">DRI website</a> for trouble-shooting information.
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</p>
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<h2>3.2 I'm seeing errors in depth (Z) buffering. Why?</h2>
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<p>
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Make sure the ratio of the far to near clipping planes isn't too great.
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Look
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<a href="http://www.sgi.com/software/opengl/advanced97/notes/node18.html">
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here</a> for details.
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</p>
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<p>
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Mesa uses a 16-bit depth buffer by default which is smaller and faster
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to clear than a 32-bit buffer but not as accurate.
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If you need a deeper you can modify the parameters to
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<code> glXChooseVisual</code> in your code.
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</p>
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<h2>3.3 Why Isn't depth buffering working at all?</h2>
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<p>
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Be sure you're requesting a depth buffered-visual. If you set the MESA_DEBUG
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environment variable it will warn you about trying to enable depth testing
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when you don't have a depth buffer.
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</p>
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<p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
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with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
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called with a non-zero value for GLX_DEPTH_SIZE.
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</p>
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<p>This discussion applies to stencil buffers, accumulation buffers and
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alpha channels too.
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</p>
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<h2>3.4 Why does glGetString() always return NULL?</h2>
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<p>
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Be sure you have an active/current OpenGL rendering context before
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calling glGetString.
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</p>
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<h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
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<p>
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If you're trying to draw a filled region by using GL_POINTS or GL_LINES
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and seeing holes or gaps it's because of a float-to-int rounding problem.
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But this is not a bug.
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See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
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Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
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will fix the problem.
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</p>
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<br>
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<br>
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<a name="part4">
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</a><h1><a name="part4">4. Developer Questions</a></h1>
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<h2><a name="part4">4.1 How can I contribute?</a></h2>
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<p>
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<a name="part4">First, join the Mesa3d-dev mailing list. That's where Mesa development
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is discussed.
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</a></p>
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<p>
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<a name="part4">The </a><a href="http://www.opengl.org/developers/documentation/specs.html">
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OpenGL Specification</a> is the bible for OpenGL implemention work.
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You should read it.
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</p>
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<p>Most of the Mesa development work involves implementing new OpenGL
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extensions, writing hardware drivers (for the DRI), and code optimization.
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</p>
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<h2>4.2 How do I write a new device driver?</h2>
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<p>
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Unfortunately, writing a device driver isn't easy.
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It requires detailed understanding of OpenGL, the Mesa code, and your
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target hardware/operating system.
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3D graphics are not simple.
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</p>
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<p>
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The best way to get started is to use an existing driver as your starting
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point.
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For a software driver, the X11 and OSMesa drivers are good examples.
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For a hardware driver, the Radeon and R200 DRI drivers are good examples.
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</p>
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<p>The DRI website has more information about writing hardware drivers.
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The process isn't well document because the Mesa driver interface changes
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over time, and we seldome have spare time for writing documentation.
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That being said, many people have managed to figure out the process.
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</p>
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<p>
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Joining the appropriate mailing lists and asking questions (and searching
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the archives) is a good way to get information.
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</p>
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</body>
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</html>
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