docs/faq.html - fp2-dev/platform/external/mesa3d - Gitiles

 <html>

 <head><title>Mesa FAQ</title></head>

 <BODY text="#000000" bgcolor="#55bbff" link="#111188">


 <center>
 <h1>Mesa Frequently Asked Questions</h1>
 Last updated: 27 April 2004
 </center>

 <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>


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

 <h2><a name="part1">1.1 What is Mesa?</a></h2>
 <p>
 <a name="part1">Mesa is an open-source implementation of the OpenGL specification.
 OpenGL is a programming library for writing interactive 3D applications.
 See the </a><a href="http://www.opengl.org/">OpenGL website</a> for more
 information.
 </p>
 <p>
 Mesa 5.x supports the OpenGL 1.4 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
 XFree86/DRI OpenGL drivers.  See the <a href="http://dri.sf.net/">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 (software-based rendering) 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/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 How do I upgrade my DRI installation to use a new Mesa release?</h2>
 <p>
 You don't!  A copy of the Mesa source code lives inside the XFree86/DRI source
 tree and gets compiled into the individual DRI driver modules.
 If you try to install Mesa over an XFree86/DRI installation, you'll lose
 hardware rendering (because stand-alone Mesa's libGL.so is different than
 the XFree86 libGL.so).
 </p>
 <p>
 The DRI developers will incorporate the latest release of Mesa into the
 DRI drivers when the time is right.
 </p>
 <p>
 To upgrade, either look for a new release of <a href="http://www.xfree86.org"
 target="_parent">XFree86</a> or visit the
 <a href="http://dri.sf.net" target="_parent">DRI website</a> to see
 if there's newer drivers.
 </p>


 <h2>1.5 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>
 There may be other open OpenGL implementations, but Mesa is the most
 popular and feature-complete.
 </p>

 <br>
 <br>


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


 <h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2>
 <p>
 <a name="part2">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.
 </a></p>


 <h2><a name="part2">2.2 Running <code>configure; make</code> Doesn't Work</a></h2>
 <p>
 <a name="part2">Unfortunately, the GNU autoconf/automake/libtool system doesn't seem to work
 too well on non GNU/Linux systems, even after installing gmake, gcc, etc.
 For that reason, Mesa's <b>old-style</b> makefile system is still included.
 The old-style system uses good old traditional Makefiles.  Try the following:
 </a></p><pre><a name="part2">  cd Mesa-x.y.z
   cp Makefile.X11 Makefile
   make
 </a></pre>
 <a name="part2">You'll see a list of system configurations from which to choose.
 For example:
 </a><pre><a name="part2">  make linux-x86
 </a></pre>
 <p>
 <a name="part2">If you're experienced with GNU autoconf/automake/libtool and think you can help
 with maintence, contact the Mesa developers.
 FYI, the Mesa developers generally don't use the autoconf/automake system.
 We're especially annoyed with the fact that a +5000-line script (libtool)
 is needed to make shared libraries (ugh).
 </a></p>

 <h2><a name="part2">2.3 Mesa still doesn't compile</a></h2>
 <p>
 <a name="part2">If the old-style Makefile system doesn't work either, make sure you have
 the most recent version of Mesa.
 Otherwise, file a bug report or post to the Mesa3d-users mailing list.
 Give as much info as possible when describing your problem.
 </a></p>


 <h2><a name="part2">2.4 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2>
 <p>
 <a name="part2">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.
 </a></p>


 <h2><a name="part2">2.5 Where is the GLUT library?</a></h2>
 <p>
 <a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaDemos-x.y.z.tar.gz file.
 If you don't already have GLUT installed, you should grab the MesaDemos
 package and unpack it before compiling Mesa.
 </a></p>


 <h2><a name="part2">2.6 What's the proper place for the libraries and headers?</a></h2>
 <p>
 <a name="part2">On Linux-based systems you'll want to follow the
 </a><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><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1
 </li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz
 </li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library.  xyz denotes the Mesa
 version number.
 </li></ul>
 <p>
 After installing XFree86 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>


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

 <h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2>
 <p>
 <a name="part3">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).
 </a></p>
 <p>
 <a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
 for your particular hardware.
 </a></p>
 <p>
 <a name="part3">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.
 </a></p>
 <p>
 <a name="part3">If your DRI-based driver isn't working, go to the
 </a><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.sgi.com/software/opengl/advanced97/notes/node18.html"
 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>

 <br>
 <br>


 <a name="part4">
 </a><h1><a name="part4">4. Developer Questions</a></h1>

 <h2><a name="part4">4.1 How can I contribute?</a></h2>
 <p>
 <a name="part4">First, join the Mesa3d-dev mailing list.  That's where Mesa development
 is discussed.
 </a></p>
 <p>
 <a name="part4">The </a><a href="http://www.opengl.org/developers/documentation/specs.html" 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 and/or the DRI drivers?</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>
 Until we can get official permission to do so, this extension will not
 be implemented in Mesa.
 </p>


 </body>
 </html>
	<html>

	<head><title>Mesa FAQ</title></head>

	<BODY text="#000000" bgcolor="#55bbff" link="#111188">


	<center>
	<h1>Mesa Frequently Asked Questions</h1>
	Last updated: 27 April 2004
	</center>

	<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>



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

	<h2><a name="part1">1.1 What is Mesa?</a></h2>
	<p>
	<a name="part1">Mesa is an open-source implementation of the OpenGL specification.
	OpenGL is a programming library for writing interactive 3D applications.
	See the </a><a href="http://www.opengl.org/">OpenGL website</a> for more
	information.
	</p>
	<p>
	Mesa 5.x supports the OpenGL 1.4 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
	XFree86/DRI OpenGL drivers. See the <a href="http://dri.sf.net/">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 (software-based rendering) 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/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 How do I upgrade my DRI installation to use a new Mesa release?</h2>
	<p>
	You don't! A copy of the Mesa source code lives inside the XFree86/DRI source
	tree and gets compiled into the individual DRI driver modules.
	If you try to install Mesa over an XFree86/DRI installation, you'll lose
	hardware rendering (because stand-alone Mesa's libGL.so is different than
	the XFree86 libGL.so).
	</p>
	<p>
	The DRI developers will incorporate the latest release of Mesa into the
	DRI drivers when the time is right.
	</p>
	<p>
	To upgrade, either look for a new release of <a href="http://www.xfree86.org"
	target="_parent">XFree86</a> or visit the
	<a href="http://dri.sf.net" target="_parent">DRI website</a> to see
	if there's newer drivers.
	</p>


	<h2>1.5 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>
	There may be other open OpenGL implementations, but Mesa is the most
	popular and feature-complete.
	</p>

	<br>
	<br>


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


	<h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2>
	<p>
	<a name="part2">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.
	</a></p>


	<h2><a name="part2">2.2 Running <code>configure; make</code> Doesn't Work</a></h2>
	<p>
	<a name="part2">Unfortunately, the GNU autoconf/automake/libtool system doesn't seem to work
	too well on non GNU/Linux systems, even after installing gmake, gcc, etc.
	For that reason, Mesa's <b>old-style</b> makefile system is still included.
	The old-style system uses good old traditional Makefiles. Try the following:
	</a></p><pre><a name="part2"> cd Mesa-x.y.z
	cp Makefile.X11 Makefile
	make
	</a></pre>
	<a name="part2">You'll see a list of system configurations from which to choose.
	For example:
	</a><pre><a name="part2"> make linux-x86
	</a></pre>
	<p>
	<a name="part2">If you're experienced with GNU autoconf/automake/libtool and think you can help
	with maintence, contact the Mesa developers.
	FYI, the Mesa developers generally don't use the autoconf/automake system.
	We're especially annoyed with the fact that a +5000-line script (libtool)
	is needed to make shared libraries (ugh).
	</a></p>

	<h2><a name="part2">2.3 Mesa still doesn't compile</a></h2>
	<p>
	<a name="part2">If the old-style Makefile system doesn't work either, make sure you have
	the most recent version of Mesa.
	Otherwise, file a bug report or post to the Mesa3d-users mailing list.
	Give as much info as possible when describing your problem.
	</a></p>


	<h2><a name="part2">2.4 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2>
	<p>
	<a name="part2">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.
	</a></p>


	<h2><a name="part2">2.5 Where is the GLUT library?</a></h2>
	<p>
	<a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaDemos-x.y.z.tar.gz file.
	If you don't already have GLUT installed, you should grab the MesaDemos
	package and unpack it before compiling Mesa.
	</a></p>



	<h2><a name="part2">2.6 What's the proper place for the libraries and headers?</a></h2>
	<p>
	<a name="part2">On Linux-based systems you'll want to follow the
	</a><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><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1
	</li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz
	</li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library. xyz denotes the Mesa
	version number.
	</li></ul>
	<p>
	After installing XFree86 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>


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

	<h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2>
	<p>
	<a name="part3">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).
	</a></p>
	<p>
	<a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
	for your particular hardware.
	</a></p>
	<p>
	<a name="part3">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.
	</a></p>
	<p>
	<a name="part3">If your DRI-based driver isn't working, go to the
	</a><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.sgi.com/software/opengl/advanced97/notes/node18.html"
	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>

	<br>
	<br>


	<a name="part4">
	</a><h1><a name="part4">4. Developer Questions</a></h1>

	<h2><a name="part4">4.1 How can I contribute?</a></h2>
	<p>
	<a name="part4">First, join the Mesa3d-dev mailing list. That's where Mesa development
	is discussed.
	</a></p>
	<p>
	<a name="part4">The </a><a href="http://www.opengl.org/developers/documentation/specs.html" 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 and/or the DRI drivers?</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>
	Until we can get official permission to do so, this extension will not
	be implemented in Mesa.
	</p>


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