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1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html lang="en"> 3<head> 4 <meta http-equiv="content-type" content="text/html; charset=utf-8"> 5 <title>Mesa FAQ</title> 6 <link rel="stylesheet" type="text/css" href="mesa.css"> 7</head> 8<body> 9 10<center> 11<h1>Mesa Frequently Asked Questions</h1> 12Last updated: 21 August 2006 13</center> 14 15<br> 16<br> 17<h2>Index</h2> 18<a href="#part1">1. High-level Questions and Answers</a> 19<br> 20<a href="#part2">2. Compilation and Installation Problems</a> 21<br> 22<a href="#part3">3. Runtime / Rendering Problems</a> 23<br> 24<a href="#part4">4. Developer Questions</a> 25<br> 26<br> 27<br> 28 29 30 31<h1 id="part1">1. High-level Questions and Answers</h1> 32 33<h2>1.1 What is Mesa?</h2> 34<p> 35Mesa is an open-source implementation of the OpenGL specification. 36OpenGL is a programming library for writing interactive 3D applications. 37See the <a href="http://www.opengl.org/">OpenGL website</a> for more 38information. 39</p> 40<p> 41Mesa 6.x supports the OpenGL 1.5 specification. 42</p> 43 44 45<h2>1.2 Does Mesa support/use graphics hardware?</h2> 46<p> 47Yes. Specifically, Mesa serves as the OpenGL core for the open-source DRI 48drivers for XFree86/X.org. See the <a href="http://dri.freedesktop.org/">DRI 49website</a> for more information. 50</p> 51<p> 52There have been other hardware drivers for Mesa over the years (such as 53the 3Dfx Glide/Voodoo driver, an old S3 driver, etc) but the DRI drivers 54are the modern ones. 55</p> 56 57<h2>1.3 What purpose does Mesa serve today?</h2> 58<p> 59Hardware-accelerated OpenGL implementations are available for most popular 60operating systems today. 61Still, Mesa serves at least these purposes: 62</p> 63<ul> 64<li>Mesa is used as the core of the open-source XFree86/X.org DRI 65 hardware drivers. 66</li> 67<li>Mesa is quite portable and allows OpenGL to be used on systems 68 that have no other OpenGL solution. 69</li> 70<li>Software rendering with Mesa serves as a reference for validating the 71 hardware drivers. 72</li> 73<li>A software implementation of OpenGL is useful for experimentation, 74 such as testing new rendering techniques. 75</li> 76<li>Mesa can render images with deep color channels: 16-bit integer 77 and 32-bit floating point color channels are supported. 78 This capability is only now appearing in hardware. 79</li> 80<li>Mesa's internal limits (max lights, clip planes, texture size, etc) can be 81 changed for special needs (hardware limits are hard to overcome). 82</li> 83</ul> 84 85 86<h2>1.4 What's the difference between"Stand-Alone" Mesa and the DRI drivers?</h2> 87<p> 88<em>Stand-alone Mesa</em> is the original incarnation of Mesa. 89On systems running the X Window System it does all its rendering through 90the Xlib API: 91</p> 92<ul> 93<li>The GLX API is supported, but it's really just an emulation of the 94 real thing. 95<li>The GLX wire protocol is not supported and there's no OpenGL extension 96 loaded by the X server. 97<li>There is no hardware acceleration. 98<li>The OpenGL library, libGL.so, contains everything (the programming API, 99 the GLX functions and all the rendering code). 100</ul> 101<p> 102Alternately, Mesa acts as the core for a number of OpenGL hardware drivers 103within the DRI (Direct Rendering Infrastructure): 104<ul> 105<li>The libGL.so library provides the GL and GLX API functions, a GLX 106 protocol encoder, and a device driver loader. 107<li>The device driver modules (such as r200_dri.so) contain a built-in 108 copy of the core Mesa code. 109<li>The X server loads the GLX module. 110 The GLX module decodes incoming GLX protocol and dispatches the commands 111 to a rendering module. 112 For the DRI, this module is basically a software Mesa renderer. 113</ul> 114 115 116 117<h2>1.5 How do I upgrade my DRI installation to use a new Mesa release?</h2> 118<p> 119This wasn't easy in the past. 120Now, the DRI drivers are included in the Mesa tree and can be compiled 121separately from the X server. 122Just follow the Mesa <a href="install.html">compilation instructions</a>. 123</p> 124 125 126<h2>1.6 Are there other open-source implementations of OpenGL?</h2> 127<p> 128Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html" 129target="_parent"> 130OpenGL Sample Implemenation (SI)</a> is available. 131The SI was written during the time that OpenGL was originally designed. 132Unfortunately, development of the SI has stagnated. 133Mesa is much more up to date with modern features and extensions. 134</p> 135 136<p> 137<a href="http://ogl-es.sourceforge.net" target="_parent">Vincent</a> is 138an open-source implementation of OpenGL ES for mobile devices. 139 140<p> 141<a href="http://www.dsbox.com/minigl.html" target="_parent">miniGL</a> 142is a subset of OpenGL for PalmOS devices. 143 144<p> 145<a href="http://fabrice.bellard.free.fr/TinyGL/" 146target="_parent">TinyGL</a> is a subset of OpenGL. 147</p> 148 149<p> 150<a href="http://softgl.studierstube.org/" target="_parent">SoftGL</a> 151is an OpenGL subset for mobile devices. 152</p> 153 154<p> 155<a href="http://chromium.sourceforge.net/" target="_parent">Chromium</a> 156isn't a conventional OpenGL implementation (it's layered upon OpenGL), 157but it does export the OpenGL API. It allows tiled rendering, sort-last 158rendering, etc. 159</p> 160 161<p> 162<a href="http://www.ticalc.org/archives/files/fileinfo/361/36173.html" 163target="_parent">ClosedGL</a> is an OpenGL subset library for TI 164graphing calculators. 165</p> 166 167<p> 168There may be other open OpenGL implementations, but Mesa is the most 169popular and feature-complete. 170</p> 171 172 173 174<br> 175<br> 176 177 178<h1 id="part2">2. Compilation and Installation Problems</h1> 179 180 181<h2>2.1 What's the easiest way to install Mesa?</h2> 182<p> 183If you're using a Linux-based system, your distro CD most likely already 184has Mesa packages (like RPM or DEB) which you can easily install. 185</p> 186 187 188<h2>2.2 I get undefined symbols such as bgnpolygon, v3f, etc...</h2> 189<p> 190You're application is written in IRIS GL, not OpenGL. 191IRIS GL was the predecessor to OpenGL and is a different thing (almost) 192entirely. 193Mesa's not the solution. 194</p> 195 196 197<h2>2.3 Where is the GLUT library?</h2> 198<p> 199GLUT (OpenGL Utility Toolkit) is no longer in the separate MesaGLUT-x.y.z.tar.gz file. 200If you don't already have GLUT installed, you should grab 201<a href="http://freeglut.sourceforge.net/">freeglut</a>. 202</p> 203 204 205<h2>2.4 Where is the GLw library?</h2> 206<p> 207GLw (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. 208</p> 209 210 211<h2>2.5 What's the proper place for the libraries and headers?</h2> 212<p> 213On Linux-based systems you'll want to follow the 214<a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html" 215target="_parent">Linux ABI</a> standard. 216Basically you'll want the following: 217</p> 218<ul> 219<li>/usr/include/GL/gl.h - the main OpenGL header 220</li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header 221</li><li>/usr/include/GL/glx.h - the OpenGL GLX header 222</li><li>/usr/include/GL/glext.h - the OpenGL extensions header 223</li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header 224</li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header 225</li><li>/usr/lib/libGL.so - a symlink to libGL.so.1 226</li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz 227</li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library. xyz denotes the 228Mesa version number. 229</li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1 230</li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz 231</li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library. xyz denotes the Mesa 232version number. 233</li></ul> 234<p> 235After installing XFree86/X.org and the DRI drivers, some of these files 236may be symlinks into the /usr/X11R6/ tree. 237</p> 238<p> 239The old-style Makefile system doesn't install the Mesa libraries; it's 240up to you to copy them (and the headers) to the right place. 241</p> 242<p> 243The GLUT header and library should go in the same directories. 244</p> 245<br> 246<br> 247 248 249<h1 id="part3">3. Runtime / Rendering Problems</h1> 250 251<h2>3.1 Rendering is slow / why isn't my graphics hardware being used?</h2> 252<p> 253Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any 254support for hardware acceleration (with the exception of the 3DFX Voodoo 255driver). 256</p> 257<p> 258What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver 259for your particular hardware. 260</p> 261<p> 262You can run the <code>glxinfo</code> program to learn about your OpenGL 263library. 264Look for the GL_VENDOR and GL_RENDERER values. 265That will identify who's OpenGL library you're using and what sort of 266hardware it has detected. 267</p> 268<p> 269If your DRI-based driver isn't working, go to the 270<a href="http://dri.sf.net/" target="_parent">DRI website</a> for trouble-shooting information. 271</p> 272 273 274<h2>3.2 I'm seeing errors in depth (Z) buffering. Why?</h2> 275<p> 276Make sure the ratio of the far to near clipping planes isn't too great. 277Look 278<a href="http://www.opengl.org/resources/faq/technical/depthbuffer.htm#0040" 279target="_parent"> here</a> for details. 280</p> 281<p> 282Mesa uses a 16-bit depth buffer by default which is smaller and faster 283to clear than a 32-bit buffer but not as accurate. 284If you need a deeper you can modify the parameters to 285<code> glXChooseVisual</code> in your code. 286</p> 287 288 289<h2>3.3 Why Isn't depth buffering working at all?</h2> 290<p> 291Be sure you're requesting a depth buffered-visual. If you set the MESA_DEBUG 292environment variable it will warn you about trying to enable depth testing 293when you don't have a depth buffer. 294</p> 295<p>Specifically, make sure <code>glutInitDisplayMode</code> is being called 296with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being 297called with a non-zero value for GLX_DEPTH_SIZE. 298</p> 299<p>This discussion applies to stencil buffers, accumulation buffers and 300alpha channels too. 301</p> 302 303 304<h2>3.4 Why does glGetString() always return NULL?</h2> 305<p> 306Be sure you have an active/current OpenGL rendering context before 307calling glGetString. 308</p> 309 310 311<h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2> 312<p> 313If you're trying to draw a filled region by using GL_POINTS or GL_LINES 314and seeing holes or gaps it's because of a float-to-int rounding problem. 315But this is not a bug. 316See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips". 317Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates 318will fix the problem. 319</p> 320 321<h2>3.6 How can I change the maximum framebuffer size in Mesa's 322<tt>swrast</tt> backend?</h2> 323<p> 324These can be overridden by using the <tt>--with-max-width</tt> and 325<tt>--with-max-height</tt> options. The two need not be equal. 326</p><p> 327Do note that Mesa uses these values to size some internal buffers, 328so increasing these sizes will cause Mesa to require additional 329memory. Furthermore, increasing these limits beyond <tt>4096</tt> 330may introduce rasterization artifacts; see the leading comments in 331<tt>src/mesa/swrast/s_tritemp.h</tt>. 332</p> 333 334<br> 335<br> 336 337 338<h1 id="part4">4. Developer Questions</h1> 339 340<h2>4.1 How can I contribute?</h2> 341<p> 342First, join the <a href="http://www.mesa3d.org/lists.html">Mesa3d-dev 343mailing list</a>. 344That's where Mesa development is discussed. 345</p> 346<p> 347The <a href="http://www.opengl.org/documentation" target="_parent"> 348OpenGL Specification</a> is the bible for OpenGL implemention work. 349You should read it. 350</p> 351<p>Most of the Mesa development work involves implementing new OpenGL 352extensions, writing hardware drivers (for the DRI), and code optimization. 353</p> 354 355<h2>4.2 How do I write a new device driver?</h2> 356<p> 357Unfortunately, writing a device driver isn't easy. 358It requires detailed understanding of OpenGL, the Mesa code, and your 359target hardware/operating system. 3603D graphics are not simple. 361</p> 362<p> 363The best way to get started is to use an existing driver as your starting 364point. 365For a software driver, the X11 and OSMesa drivers are good examples. 366For a hardware driver, the Radeon and R200 DRI drivers are good examples. 367</p> 368<p>The DRI website has more information about writing hardware drivers. 369The process isn't well document because the Mesa driver interface changes 370over time, and we seldome have spare time for writing documentation. 371That being said, many people have managed to figure out the process. 372</p> 373<p> 374Joining the appropriate mailing lists and asking questions (and searching 375the archives) is a good way to get information. 376</p> 377 378 379<h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa?</h2> 380<p> 381The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a> 382indicates that there are intellectual property (IP) and/or patent issues 383to be dealt with. 384</p> 385<p>We've been unsucessful in getting a response from S3 (or whoever owns 386the IP nowadays) to indicate whether or not an open source project can 387implement the extension (specifically the compression/decompression 388algorithms). 389</p> 390<p> 391In the mean time, a 3rd party <a href= 392"http://homepage.hispeed.ch/rscheidegger/dri_experimental/s3tc_index.html" 393target="_parent">plug-in library</a> is available. 394</p> 395 396 397</body> 398</html> 399