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  11 <h1>Mesa Frequently Asked Questions</h1>
  12 Last updated: 17 November 2004
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  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.
  37 OpenGL is a programming library for writing interactive 3D applications.
  38 See the </a><a href="http://www.opengl.org/">OpenGL website</a> for more
  39 information.
  40 </p>
  41 <p>
  42 Mesa 5.x supports the OpenGL 1.4 specification.
  43 </p>
  44
  45
  46 <h2>1.2 Does Mesa support/use graphics hardware?</h2>
  47 <p>
  48 Yes.  Specifically, Mesa serves as the OpenGL core for the open-source
  49 XFree86/DRI OpenGL drivers.  See the <a href="http://dri.sf.net/">DRI
  50 website</a> for more information.
  51 </p>
  52 <p>
  53 There have been other hardware drivers for Mesa over the years (such as
  54 the 3Dfx Glide/Voodoo driver, an old S3 driver, etc) but the DRI drivers
  55 are the modern ones.
  56 </p>
  57
  58 <h2>1.3 What purpose does Mesa serve today?</h2>
  59 <p>
  60 Hardware-accelerated OpenGL implementations are available for most popular
  61 operating systems today.
  62 Still, Mesa serves at least these purposes:
  63 </p>
  64 <ul>
  65 <li>Mesa is used as the core of the open-source XFree86/DRI 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.
  89 On systems running the X Window System, it does all its rendering through
  90 the Xlib API.
  91 <ul>
  92 <li>The GLX API is supported, but it's really just an emulation of the
  93      real thing.
  94 <li>The GLX wire protocol is not supported and there's no OpenGL extension
  95     loaded by the X server.
  96 <li>There is no hardware acceleration.
  97 <li>The OpenGL library, libGL.so, contains everything (the programming API,
  98     the GLX functions and all the rendering code).
  99 </ul>
 100 </p>
 101 <p>
 102 Alternately, Mesa acts as the core for a number of OpenGL hardware drivers
 103 within 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>
 119 You don't!  A copy of the Mesa source code lives inside the XFree86/DRI source
 120 tree and gets compiled into the individual DRI driver modules.
 121 If you try to install Mesa over an XFree86/DRI installation, you'll lose
 122 hardware rendering (because stand-alone Mesa's libGL.so is different than
 123 the XFree86 libGL.so).
 124 </p>
 125 <p>
 126 The DRI developers will incorporate the latest release of Mesa into the
 127 DRI drivers when the time is right.
 128 </p>
 129 <p>
 130 To upgrade, either look for a new release of <a href="http://www.xfree86.org"
 131 target="_parent">XFree86</a> or visit the
 132 <a href="http://dri.sf.net" target="_parent">DRI website</a> to see
 133 if there's newer drivers.
 134 </p>
 135
 136
 137 <h2>1.6 Are there other open-source implementations of OpenGL?</h2>
 138 <p>
 139 Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html"
 140 target="_parent">
 141 OpenGL Sample Implemenation (SI)</a> is available.
 142 The SI was written during the time that OpenGL was originally designed.
 143 Unfortunately, development of the SI has stagnated.
 144 Mesa is much more up to date with modern features and extensions.
 145 </p>
 146
 147 <p>
 148 <a href="http://ogl-es.sourceforge.net" target="_parent">Vincent</a> is
 149 an open-source implementation of OpenGL ES for mobile devices.
 150
 151 <p>
 152 <a href="http://www.dsbox.com/minigl.html" target="_parent">miniGL</a>
 153 is a subset of OpenGL for PalmOS devices.
 154
 155 <p>
 156 <a href="http://fabrice.bellard.free.fr/TinyGL/"
 157 target="_parent">TinyGL</a> is a subset of OpenGL.
 158 </p>
 159
 160 <p>
 161 <a href="http://softgl.studierstube.org/" target="_parent">SoftGL</a>
 162 is an OpenGL subset for mobile devices.
 163 </p>
 164
 165 <p>
 166 <a href="http://chromium.sourceforge.net/" target="_parent">Chromium</a>
 167 isn't a conventional OpenGL implementation (it's layered upon OpenGL),
 168 but it does export the OpenGL API.  It allows tiled rendering, sort-last
 169 rendering, etc.
 170 </p>
 171
 172 <p>
 173 There may be other open OpenGL implementations, but Mesa is the most
 174 popular and feature-complete.
 175 </p>
 176
 177
 178
 179 <br>
 180 <br>
 181
 182
 183 <a name="part2">
 184 </a><h1><a name="part2">2. Compilation and Installation Problems</a></h1>
 185
 186
 187 <h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2>
 188 <p>
 189 <a name="part2">If you're using a Linux-based system, your distro CD most likely already
 190 has Mesa packages (like RPM or DEB) which you can easily install.
 191 </a></p>
 192
 193
 194 <h2><a name="part2">2.2 Running <code>configure; make</code> doesn't Work</a></h2>
 195 <p>
 196 Mesa no longer supports GNU autoconf/automake.  Why?
 197 <ul>
 198 <li>It seemed to seldom work on anything but Linux
 199 <li>The config files were hard to maintain and hard to understand
 200 <li>libtool caused a lot of grief
 201 </ul>
 202
 203 <p>
 204 Now, Mesa again uses a conventional Makefile system (as it did originally).
 205 Basically, each Makefile in the tree includes one of the configuration
 206 files from the config/ directory.
 207 The config files specify all the variables for a variety of popular systems.
 208 </p>
 209
 210
 211 <h2><a name="part2">2.3 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2>
 212 <p>
 213 <a name="part2">You're application is written in IRIS GL, not OpenGL.
 214 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 215 entirely.
 216 Mesa's not the solution.
 217 </a></p>
 218
 219
 220 <h2><a name="part2">2.4 Where is the GLUT library?</a></h2>
 221 <p>
 222 <a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaDemos-x.y.z.tar.gz file.
 223 If you don't already have GLUT installed, you should grab the MesaDemos
 224 package and unpack it before compiling Mesa.
 225 </a></p>
 226
 227
 228
 229 <h2><a name="part2">2.5 What's the proper place for the libraries and headers?</a></h2>
 230 <p>
 231 <a name="part2">On Linux-based systems you'll want to follow the
 232 </a><a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html"
 233 target="_parent">Linux ABI</a> standard.
 234 Basically you'll want the following:
 235 </p>
 236 <ul>
 237 <li>/usr/include/GL/gl.h - the main OpenGL header
 238 </li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
 239 </li><li>/usr/include/GL/glx.h - the OpenGL GLX header
 240 </li><li>/usr/include/GL/glext.h - the OpenGL extensions header
 241 </li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
 242 </li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
 243 </li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
 244 </li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
 245 </li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library.  xyz denotes the
 246 Mesa version number.
 247 </li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1
 248 </li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz
 249 </li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library.  xyz denotes the Mesa
 250 version number.
 251 </li></ul>
 252 <p>
 253 After installing XFree86 and the DRI drivers, some of these files
 254 may be symlinks into the /usr/X11R6/ tree.
 255 </p>
 256 <p>
 257 The old-style Makefile system doesn't install the Mesa libraries; it's
 258 up to you to copy them (and the headers) to the right place.
 259 </p>
 260 <p>
 261 The GLUT header and library should go in the same directories.
 262 </p>
 263 <br>
 264 <br>
 265
 266
 267 <a name="part3">
 268 </a><h1><a name="part3">3. Runtime / Rendering Problems</a></h1>
 269
 270 <h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2>
 271 <p>
 272 <a name="part3">Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any
 273 support for hardware acceleration (with the exception of the 3DFX Voodoo
 274 driver).
 275 </a></p>
 276 <p>
 277 <a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
 278 for your particular hardware.
 279 </a></p>
 280 <p>
 281 <a name="part3">You can run the <code>glxinfo</code> program to learn about your OpenGL
 282 library.
 283 Look for the GL_VENDOR and GL_RENDERER values.
 284 That will identify who's OpenGL library you're using and what sort of
 285 hardware it has detected.
 286 </a></p>
 287 <p>
 288 <a name="part3">If your DRI-based driver isn't working, go to the
 289 </a><a href="http://dri.sf.net/" target="_parent">DRI website</a> for trouble-shooting information.
 290 </p>
 291
 292
 293 <h2>3.2 I'm seeing errors in depth (Z) buffering.  Why?</h2>
 294 <p>
 295 Make sure the ratio of the far to near clipping planes isn't too great.
 296 Look
 297 <a href="http://www.sgi.com/software/opengl/advanced97/notes/node18.html"
 298 target="_parent">
 299 here</a> for details.
 300 </p>
 301 <p>
 302 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 303 to clear than a 32-bit buffer but not as accurate.
 304 If you need a deeper you can modify the parameters to
 305 <code> glXChooseVisual</code> in your code.
 306 </p>
 307
 308
 309 <h2>3.3 Why Isn't depth buffering working at all?</h2>
 310 <p>
 311 Be sure you're requesting a depth buffered-visual.  If you set the MESA_DEBUG
 312 environment variable it will warn you about trying to enable depth testing
 313 when you don't have a depth buffer.
 314 </p>
 315 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 316 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 317 called with a non-zero value for GLX_DEPTH_SIZE.
 318 </p>
 319 <p>This discussion applies to stencil buffers, accumulation buffers and
 320 alpha channels too.
 321 </p>
 322
 323
 324 <h2>3.4 Why does glGetString() always return NULL?</h2>
 325 <p>
 326 Be sure you have an active/current OpenGL rendering context before
 327 calling glGetString.
 328 </p>
 329
 330
 331 <h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
 332 <p>
 333 If you're trying to draw a filled region by using GL_POINTS or GL_LINES
 334 and seeing holes or gaps it's because of a float-to-int rounding problem.
 335 But this is not a bug.
 336 See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
 337 Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
 338 will fix the problem.
 339 </p>
 340
 341 <br>
 342 <br>
 343
 344
 345 <a name="part4">
 346 </a><h1><a name="part4">4. Developer Questions</a></h1>
 347
 348 <h2><a name="part4">4.1 How can I contribute?</a></h2>
 349 <p>
 350 <a name="part4">First, join the Mesa3d-dev mailing list.  That's where Mesa development
 351 is discussed.
 352 </a></p>
 353 <p>
 354 <a name="part4">The </a><a href="http://www.opengl.org/developers/documentation/specs.html" target="_parent">
 355 OpenGL Specification</a> is the bible for OpenGL implemention work.
 356 You should read it.
 357 </p>
 358 <p>Most of the Mesa development work involves implementing new OpenGL
 359 extensions, writing hardware drivers (for the DRI), and code optimization.
 360 </p>
 361
 362 <h2>4.2 How do I write a new device driver?</h2>
 363 <p>
 364 Unfortunately, writing a device driver isn't easy.
 365 It requires detailed understanding of OpenGL, the Mesa code, and your
 366 target hardware/operating system.
 367 3D graphics are not simple.
 368 </p>
 369 <p>
 370 The best way to get started is to use an existing driver as your starting
 371 point.
 372 For a software driver, the X11 and OSMesa drivers are good examples.
 373 For a hardware driver, the Radeon and R200 DRI drivers are good examples.
 374 </p>
 375 <p>The DRI website has more information about writing hardware drivers.
 376 The process isn't well document because the Mesa driver interface changes
 377 over time, and we seldome have spare time for writing documentation.
 378 That being said, many people have managed to figure out the process.
 379 </p>
 380 <p>
 381 Joining the appropriate mailing lists and asking questions (and searching
 382 the archives) is a good way to get information.
 383 </p>
 384
 385
 386 <h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa and/or the DRI drivers?</h2>
 387 <p>
 388 The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a>
 389 indicates that there are intellectual property (IP) and/or patent issues
 390 to be dealt with.
 391 </p>
 392 <p>We've been unsucessful in getting a response from S3 (or whoever owns
 393 the IP nowadays) to indicate whether or not an open source project can
 394 implement the extension (specifically the compression/decompression
 395 algorithms).
 396 </p>
 397 <p>
 398 Until we can get official permission to do so, this extension will not
 399 be implemented in Mesa.
 400 </p>
 401
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