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diff --git a/docs/faq.rst b/docs/faq.rst new file mode 100644 index 0000000000..8420409df8 --- /dev/null +++ b/docs/faq.rst @@ -0,0 +1,390 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html lang="en"><head> + <meta content="text/html; charset=utf-8" http-equiv="content-type"/> + <title>Mesa FAQ</title> + <link href="mesa.css" rel="stylesheet" type="text/css"/> +</head> +<body> + + + + + + +<center> +<h1>Mesa Frequently Asked Questions</h1> +Last updated: 9 October 2012 +</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/> + + + +<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="https://www.opengl.org/">OpenGL website</a> for more +information. +</p> +<p> +Mesa 9.x supports the OpenGL 3.1 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 X.org. +</p> +<ul> + <li>See the <a href="https://dri.freedesktop.org/">DRI website</a> + for more information.</li> + <li>See <a href="https://01.org/linuxgraphics">01.org</a> + for more information about Intel drivers.</li> + <li>See <a href="https://nouveau.freedesktop.org">nouveau.freedesktop.org</a> + for more information about Nouveau drivers.</li> + <li>See <a href="https://www.x.org/wiki/RadeonFeature">www.x.org/wiki/RadeonFeature</a> + for more information about Radeon drivers.</li> +</ul> + +<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> + + +<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><li>The GLX wire protocol is not supported and there's no OpenGL extension + loaded by the X server. +</li><li>There is no hardware acceleration. +</li><li>The OpenGL library, libGL.so, contains everything (the programming API, + the GLX functions and all the rendering code). +</li></ul> +<p> +Alternately, Mesa acts as the core for a number of OpenGL hardware drivers +within the DRI (Direct Rendering Infrastructure): +</p><ul> +<li>The libGL.so library provides the GL and GLX API functions, a GLX + protocol encoder, and a device driver loader. +</li><li>The device driver modules (such as r200_dri.so) contain a built-in + copy of the core Mesa code. +</li><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. +</li></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"> +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> + +<p> +<a href="https://sourceforge.net/projects/ogl-es/">Vincent</a> is +an open-source implementation of OpenGL ES for mobile devices. + +</p><p> +<a href="http://www.dsbox.com/minigl.html">miniGL</a> +is a subset of OpenGL for PalmOS devices. + +</p><p> +<a href="http://bellard.org/TinyGL/">TinyGL</a> +is a subset of OpenGL. +</p> + +<p> +<a href="https://sourceforge.net/projects/softgl/">SoftGL</a> +is an OpenGL subset for mobile devices. +</p> + +<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> + +<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> + +<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="https://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">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> +<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> +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="https://dri.freedesktop.org/">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="https://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> + + +<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/> + + +<h1 id="part4">4. Developer Questions</h1> + +<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="https://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> + +<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> + + +<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="https://dri.freedesktop.org/wiki/S3TC"> +plug-in library</a> is available. +</p> + + + + +</body></html>
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