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 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<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.freedesktop.org/">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> 163<a href="http://www.ticalc.org/archives/files/fileinfo/361/36173.html" 164target="_parent">ClosedGL</a> is an OpenGL subset library for TI 165graphing calculators. 166</p> 167 168<p> 169There may be other open OpenGL implementations, but Mesa is the most 170popular and feature-complete. 171</p> 172 173 174 175<br> 176<br> 177 178 179<a name="part2"> 180</a><h1><a name="part2">2. Compilation and Installation Problems</a></h1> 181 182 183<h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2> 184<p> 185<a name="part2">If you're using a Linux-based system, your distro CD most likely already 186has Mesa packages (like RPM or DEB) which you can easily install. 187</a></p> 188 189 190<h2><a name="part2">2.2 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2> 191<p> 192<a name="part2">You're application is written in IRIS GL, not OpenGL. 193IRIS GL was the predecessor to OpenGL and is a different thing (almost) 194entirely. 195Mesa's not the solution. 196</a></p> 197 198 199<h2><a name="part2">2.3 Where is the GLUT library?</a></h2> 200<p> 201<a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaGLUT-x.y.z.tar.gz file. 202If you don't already have GLUT installed, you should grab the MesaGLUT 203package and compile it with the rest of Mesa. 204</a></p> 205 206 207 208<h2><a name="part2">2.4 What's the proper place for the libraries and headers?</a></h2> 209<p> 210<a name="part2">On Linux-based systems you'll want to follow the 211</a><a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html" 212target="_parent">Linux ABI</a> standard. 213Basically you'll want the following: 214</p> 215<ul> 216<li>/usr/include/GL/gl.h - the main OpenGL header 217</li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header 218</li><li>/usr/include/GL/glx.h - the OpenGL GLX header 219</li><li>/usr/include/GL/glext.h - the OpenGL extensions header 220</li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header 221</li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header 222</li><li>/usr/lib/libGL.so - a symlink to libGL.so.1 223</li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz 224</li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library. xyz denotes the 225Mesa version number. 226</li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1 227</li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz 228</li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library. xyz denotes the Mesa 229version number. 230</li></ul> 231<p> 232After installing XFree86/X.org and the DRI drivers, some of these files 233may be symlinks into the /usr/X11R6/ tree. 234</p> 235<p> 236The old-style Makefile system doesn't install the Mesa libraries; it's 237up to you to copy them (and the headers) to the right place. 238</p> 239<p> 240The GLUT header and library should go in the same directories. 241</p> 242<br> 243<br> 244 245 246<a name="part3"> 247</a><h1><a name="part3">3. Runtime / Rendering Problems</a></h1> 248 249<h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2> 250<p> 251<a name="part3">Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any 252support for hardware acceleration (with the exception of the 3DFX Voodoo 253driver). 254</a></p> 255<p> 256<a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver 257for your particular hardware. 258</a></p> 259<p> 260<a name="part3">You can run the <code>glxinfo</code> program to learn about your OpenGL 261library. 262Look for the GL_VENDOR and GL_RENDERER values. 263That will identify who's OpenGL library you're using and what sort of 264hardware it has detected. 265</a></p> 266<p> 267<a name="part3">If your DRI-based driver isn't working, go to the 268</a><a href="http://dri.sf.net/" target="_parent">DRI website</a> for trouble-shooting information. 269</p> 270 271 272<h2>3.2 I'm seeing errors in depth (Z) buffering. Why?</h2> 273<p> 274Make sure the ratio of the far to near clipping planes isn't too great. 275Look 276<a href="http://www.opengl.org/resources/faq/technical/depthbuffer.htm#0040" 277target="_parent"> here</a> for details. 278</p> 279<p> 280Mesa uses a 16-bit depth buffer by default which is smaller and faster 281to clear than a 32-bit buffer but not as accurate. 282If you need a deeper you can modify the parameters to 283<code> glXChooseVisual</code> in your code. 284</p> 285 286 287<h2>3.3 Why Isn't depth buffering working at all?</h2> 288<p> 289Be sure you're requesting a depth buffered-visual. If you set the MESA_DEBUG 290environment variable it will warn you about trying to enable depth testing 291when you don't have a depth buffer. 292</p> 293<p>Specifically, make sure <code>glutInitDisplayMode</code> is being called 294with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being 295called with a non-zero value for GLX_DEPTH_SIZE. 296</p> 297<p>This discussion applies to stencil buffers, accumulation buffers and 298alpha channels too. 299</p> 300 301 302<h2>3.4 Why does glGetString() always return NULL?</h2> 303<p> 304Be sure you have an active/current OpenGL rendering context before 305calling glGetString. 306</p> 307 308 309<h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2> 310<p> 311If you're trying to draw a filled region by using GL_POINTS or GL_LINES 312and seeing holes or gaps it's because of a float-to-int rounding problem. 313But this is not a bug. 314See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips". 315Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates 316will fix the problem. 317</p> 318 319<h2>3.6 How can I change the maximum framebuffer size in Mesa's 320<tt>swrast</tt> backend?</h2> 321<p> 322These can be overridden by using the <tt>--with-max-width</tt> and 323<tt>--with-max-height</tt> options. The two need not be equal. 324</p><p> 325Do note that Mesa uses these values to size some internal buffers, 326so increasing these sizes will cause Mesa to require additional 327memory. Furthermore, increasing these limits beyond <tt>4096</tt> 328may introduce rasterization artifacts; see the leading comments in 329<tt>src/mesa/swrast/s_tritemp.h</tt>. 330</p> 331 332<br> 333<br> 334 335 336<a name="part4"> 337</a><h1><a name="part4">4. Developer Questions</a></h1> 338 339<h2>4.1 How can I contribute?</a></h2> 340<p> 341First, join the <a href="http://www.mesa3d.org/lists.html">Mesa3d-dev 342mailing list</a>. 343That's where Mesa development is discussed. 344</p> 345<p> 346The <a href="http://www.opengl.org/documentation" target="_parent"> 347OpenGL Specification</a> is the bible for OpenGL implemention work. 348You should read it. 349</p> 350<p>Most of the Mesa development work involves implementing new OpenGL 351extensions, writing hardware drivers (for the DRI), and code optimization. 352</p> 353 354<h2>4.2 How do I write a new device driver?</h2> 355<p> 356Unfortunately, writing a device driver isn't easy. 357It requires detailed understanding of OpenGL, the Mesa code, and your 358target hardware/operating system. 3593D graphics are not simple. 360</p> 361<p> 362The best way to get started is to use an existing driver as your starting 363point. 364For a software driver, the X11 and OSMesa drivers are good examples. 365For a hardware driver, the Radeon and R200 DRI drivers are good examples. 366</p> 367<p>The DRI website has more information about writing hardware drivers. 368The process isn't well document because the Mesa driver interface changes 369over time, and we seldome have spare time for writing documentation. 370That being said, many people have managed to figure out the process. 371</p> 372<p> 373Joining the appropriate mailing lists and asking questions (and searching 374the archives) is a good way to get information. 375</p> 376 377 378<h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa?</h2> 379<p> 380The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a> 381indicates that there are intellectual property (IP) and/or patent issues 382to be dealt with. 383</p> 384<p>We've been unsucessful in getting a response from S3 (or whoever owns 385the IP nowadays) to indicate whether or not an open source project can 386implement the extension (specifically the compression/decompression 387algorithms). 388</p> 389<p> 390In the mean time, a 3rd party <a href= 391"http://homepage.hispeed.ch/rscheidegger/dri_experimental/s3tc_index.html" 392target="_parent">plug-in library</a> is available. 393</p> 394 395 396</body> 397</html> 398