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1<html> 2 3<head><title>Mesa FAQ</title></head> 4 5<link rel="stylesheet" type="text/css" href="mesa.css"></head> 6 7<BODY> 8 9 10<center> 11<h1>Mesa Frequently Asked Questions</h1> 12Last updated: 21 October 2004 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<a name="part1"> 32</a><h1><a name="part1">1. High-level Questions and Answers</a></h1> 33 34<h2><a name="part1">1.1 What is Mesa?</a></h2> 35<p> 36<a name="part1">Mesa is an open-source implementation of the OpenGL specification. 37OpenGL is a programming library for writing interactive 3D applications. 38See the </a><a href="http://www.opengl.org/">OpenGL website</a> for more 39information. 40</p> 41<p> 42Mesa 6.x supports the OpenGL 1.5 specification. 43</p> 44 45 46<h2>1.2 Does Mesa support/use graphics hardware?</h2> 47<p> 48Yes. Specifically, Mesa serves as the OpenGL core for the open-source DRI 49drivers for XFree86/X.org. See the <a href="http://dri.sf.net/">DRI 50website</a> for more information. 51</p> 52<p> 53There have been other hardware drivers for Mesa over the years (such as 54the 3Dfx Glide/Voodoo driver, an old S3 driver, etc) but the DRI drivers 55are the modern ones. 56</p> 57 58<h2>1.3 What purpose does Mesa serve today?</h2> 59<p> 60Hardware-accelerated OpenGL implementations are available for most popular 61operating systems today. 62Still, Mesa serves at least these purposes: 63</p> 64<ul> 65<li>Mesa is used as the core of the open-source XFree86/X.org DRI 66 hardware drivers. 67</li> 68<li>Mesa is quite portable and allows OpenGL to be used on systems 69 that have no other OpenGL solution. 70</li> 71<li>Software rendering with Mesa serves as a reference for validating the 72 hardware drivers. 73</li> 74<li>A software implementation of OpenGL is useful for experimentation, 75 such as testing new rendering techniques. 76</li> 77<li>Mesa can render images with deep color channels: 16-bit integer 78 and 32-bit floating point color channels are supported. 79 This capability is only now appearing in hardware. 80</li> 81<li>Mesa's internal limits (max lights, clip planes, texture size, etc) can be 82 changed for special needs (hardware limits are hard to overcome). 83</li> 84</ul> 85 86 87<h2>1.4 What's the difference between"Stand-Alone" Mesa and the DRI drivers?</h2> 88<p> 89<em>Stand-alone Mesa</em> is the original incarnation of Mesa. 90On systems running the X Window System it does all its rendering through 91the Xlib API: 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> 102<p> 103Alternately, Mesa acts as the core for a number of OpenGL hardware drivers 104within the DRI (Direct Rendering Infrastructure): 105<ul> 106<li>The libGL.so library provides the GL and GLX API functions, a GLX 107 protocol encoder, and a device driver loader. 108<li>The device driver modules (such as r200_dri.so) contain a built-in 109 copy of the core Mesa code. 110<li>The X server loads the GLX module. 111 The GLX module decodes incoming GLX protocol and dispatches the commands 112 to a rendering module. 113 For the DRI, this module is basically a software Mesa renderer. 114</ul> 115 116 117 118<h2>1.5 How do I upgrade my DRI installation to use a new Mesa release?</h2> 119<p> 120This wasn't easy in the past. 121Now, the DRI drivers are included in the Mesa tree and can be compiled 122separately from the X server. 123Just follow the Mesa <a href="install.html">compilation instructions</a>. 124</p> 125 126 127<h2>1.6 Are there other open-source implementations of OpenGL?</h2> 128<p> 129Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html" 130target="_parent"> 131OpenGL Sample Implemenation (SI)</a> is available. 132The SI was written during the time that OpenGL was originally designed. 133Unfortunately, development of the SI has stagnated. 134Mesa is much more up to date with modern features and extensions. 135</p> 136 137<p> 138<a href="http://ogl-es.sourceforge.net" target="_parent">Vincent</a> is 139an open-source implementation of OpenGL ES for mobile devices. 140 141<p> 142<a href="http://www.dsbox.com/minigl.html" target="_parent">miniGL</a> 143is a subset of OpenGL for PalmOS devices. 144 145<p> 146<a href="http://fabrice.bellard.free.fr/TinyGL/" 147target="_parent">TinyGL</a> is a subset of OpenGL. 148</p> 149 150<p> 151<a href="http://softgl.studierstube.org/" target="_parent">SoftGL</a> 152is an OpenGL subset for mobile devices. 153</p> 154 155<p> 156<a href="http://chromium.sourceforge.net/" target="_parent">Chromium</a> 157isn't a conventional OpenGL implementation (it's layered upon OpenGL), 158but it does export the OpenGL API. It allows tiled rendering, sort-last 159rendering, etc. 160</p> 161 162<p> 163There may be other open OpenGL implementations, but Mesa is the most 164popular and feature-complete. 165</p> 166 167 168 169<br> 170<br> 171 172 173<a name="part2"> 174</a><h1><a name="part2">2. Compilation and Installation Problems</a></h1> 175 176 177<h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2> 178<p> 179<a name="part2">If you're using a Linux-based system, your distro CD most likely already 180has Mesa packages (like RPM or DEB) which you can easily install. 181</a></p> 182 183 184<h2><a name="part2">2.2 Running <code>configure; make</code> doesn't Work</a></h2> 185<p> 186Mesa no longer supports GNU autoconf/automake. Why? 187<ul> 188<li>It seemed to seldom work on anything but Linux 189<li>The config files were hard to maintain and hard to understand 190<li>libtool caused a lot of grief 191</ul> 192 193<p> 194Now Mesa again uses a conventional Makefile system (as it did originally). 195Basically, each Makefile in the tree includes one of the configuration 196files from the config/ directory. 197The config files specify all the variables for a variety of popular systems. 198</p> 199 200 201<h2><a name="part2">2.3 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2> 202<p> 203<a name="part2">You're application is written in IRIS GL, not OpenGL. 204IRIS GL was the predecessor to OpenGL and is a different thing (almost) 205entirely. 206Mesa's not the solution. 207</a></p> 208 209 210<h2><a name="part2">2.4 Where is the GLUT library?</a></h2> 211<p> 212<a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaGLUT-x.y.z.tar.gz file. 213If you don't already have GLUT installed, you should grab the MesaGLUT 214package and compile it with the rest of Mesa. 215</a></p> 216 217 218 219<h2><a name="part2">2.5 What's the proper place for the libraries and headers?</a></h2> 220<p> 221<a name="part2">On Linux-based systems you'll want to follow the 222</a><a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html" 223target="_parent">Linux ABI</a> standard. 224Basically you'll want the following: 225</p> 226<ul> 227<li>/usr/include/GL/gl.h - the main OpenGL header 228</li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header 229</li><li>/usr/include/GL/glx.h - the OpenGL GLX header 230</li><li>/usr/include/GL/glext.h - the OpenGL extensions header 231</li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header 232</li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header 233</li><li>/usr/lib/libGL.so - a symlink to libGL.so.1 234</li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz 235</li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library. xyz denotes the 236Mesa version number. 237</li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1 238</li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz 239</li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library. xyz denotes the Mesa 240version number. 241</li></ul> 242<p> 243After installing XFree86/X.org and the DRI drivers, some of these files 244may be symlinks into the /usr/X11R6/ tree. 245</p> 246<p> 247The old-style Makefile system doesn't install the Mesa libraries; it's 248up to you to copy them (and the headers) to the right place. 249</p> 250<p> 251The GLUT header and library should go in the same directories. 252</p> 253<br> 254<br> 255 256 257<a name="part3"> 258</a><h1><a name="part3">3. Runtime / Rendering Problems</a></h1> 259 260<h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2> 261<p> 262<a name="part3">Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any 263support for hardware acceleration (with the exception of the 3DFX Voodoo 264driver). 265</a></p> 266<p> 267<a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver 268for your particular hardware. 269</a></p> 270<p> 271<a name="part3">You can run the <code>glxinfo</code> program to learn about your OpenGL 272library. 273Look for the GL_VENDOR and GL_RENDERER values. 274That will identify who's OpenGL library you're using and what sort of 275hardware it has detected. 276</a></p> 277<p> 278<a name="part3">If your DRI-based driver isn't working, go to the 279</a><a href="http://dri.sf.net/" target="_parent">DRI website</a> for trouble-shooting information. 280</p> 281 282 283<h2>3.2 I'm seeing errors in depth (Z) buffering. Why?</h2> 284<p> 285Make sure the ratio of the far to near clipping planes isn't too great. 286Look 287<a href="http://www.sgi.com/software/opengl/advanced97/notes/node18.html" 288target="_parent"> 289here</a> for details. 290</p> 291<p> 292Mesa uses a 16-bit depth buffer by default which is smaller and faster 293to clear than a 32-bit buffer but not as accurate. 294If you need a deeper you can modify the parameters to 295<code> glXChooseVisual</code> in your code. 296</p> 297 298 299<h2>3.3 Why Isn't depth buffering working at all?</h2> 300<p> 301Be sure you're requesting a depth buffered-visual. If you set the MESA_DEBUG 302environment variable it will warn you about trying to enable depth testing 303when you don't have a depth buffer. 304</p> 305<p>Specifically, make sure <code>glutInitDisplayMode</code> is being called 306with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being 307called with a non-zero value for GLX_DEPTH_SIZE. 308</p> 309<p>This discussion applies to stencil buffers, accumulation buffers and 310alpha channels too. 311</p> 312 313 314<h2>3.4 Why does glGetString() always return NULL?</h2> 315<p> 316Be sure you have an active/current OpenGL rendering context before 317calling glGetString. 318</p> 319 320 321<h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2> 322<p> 323If you're trying to draw a filled region by using GL_POINTS or GL_LINES 324and seeing holes or gaps it's because of a float-to-int rounding problem. 325But this is not a bug. 326See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips". 327Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates 328will fix the problem. 329</p> 330 331<br> 332<br> 333 334 335<a name="part4"> 336</a><h1><a name="part4">4. Developer Questions</a></h1> 337 338<h2><a name="part4">4.1 How can I contribute?</a></h2> 339<p> 340<a name="part4">First, join the Mesa3d-dev mailing list. That's where Mesa development 341is discussed. 342</a></p> 343<p> 344<a name="part4">The </a><a href="http://www.opengl.org/developers/documentation/specs.html" target="_parent"> 345OpenGL Specification</a> is the bible for OpenGL implemention work. 346You should read it. 347</p> 348<p>Most of the Mesa development work involves implementing new OpenGL 349extensions, writing hardware drivers (for the DRI), and code optimization. 350</p> 351 352<h2>4.2 How do I write a new device driver?</h2> 353<p> 354Unfortunately, writing a device driver isn't easy. 355It requires detailed understanding of OpenGL, the Mesa code, and your 356target hardware/operating system. 3573D graphics are not simple. 358</p> 359<p> 360The best way to get started is to use an existing driver as your starting 361point. 362For a software driver, the X11 and OSMesa drivers are good examples. 363For a hardware driver, the Radeon and R200 DRI drivers are good examples. 364</p> 365<p>The DRI website has more information about writing hardware drivers. 366The process isn't well document because the Mesa driver interface changes 367over time, and we seldome have spare time for writing documentation. 368That being said, many people have managed to figure out the process. 369</p> 370<p> 371Joining the appropriate mailing lists and asking questions (and searching 372the archives) is a good way to get information. 373</p> 374 375 376<h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa and/or the DRI drivers?</h2> 377<p> 378The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a> 379indicates that there are intellectual property (IP) and/or patent issues 380to be dealt with. 381</p> 382<p>We've been unsucessful in getting a response from S3 (or whoever owns 383the IP nowadays) to indicate whether or not an open source project can 384implement the extension (specifically the compression/decompression 385algorithms). 386</p> 387<p> 388Until we can get official permission to do so, this extension will not 389be implemented in Mesa. 390</p> 391 392 393</body> 394</html> 395