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  11 <h1>Mesa Frequently Asked Questions</h1>
  12 Last updated: 21 August 2006
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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 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>
  48 Yes.  Specifically, Mesa serves as the OpenGL core for the open-source DRI
  49 drivers for XFree86/X.org.  See the <a href="http://dri.freedesktop.org/">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/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.
  90 On systems running the X Window System it does all its rendering through
  91 the 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>
 103 Alternately, Mesa acts as the core for a number of OpenGL hardware drivers
 104 within 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>
 120 This wasn't easy in the past.
 121 Now, the DRI drivers are included in the Mesa tree and can be compiled
 122 separately from the X server.
 123 Just 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>
 129 Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html"
 130 target="_parent">
 131 OpenGL Sample Implemenation (SI)</a> is available.
 132 The SI was written during the time that OpenGL was originally designed.
 133 Unfortunately, development of the SI has stagnated.
 134 Mesa 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
 139 an 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>
 143 is a subset of OpenGL for PalmOS devices.
 144
 145 <p>
 146 <a href="http://fabrice.bellard.free.fr/TinyGL/"
 147 target="_parent">TinyGL</a> is a subset of OpenGL.
 148 </p>
 149
 150 <p>
 151 <a href="http://softgl.studierstube.org/" target="_parent">SoftGL</a>
 152 is an OpenGL subset for mobile devices.
 153 </p>
 154
 155 <p>
 156 <a href="http://chromium.sourceforge.net/" target="_parent">Chromium</a>
 157 isn't a conventional OpenGL implementation (it's layered upon OpenGL),
 158 but it does export the OpenGL API.  It allows tiled rendering, sort-last
 159 rendering, etc.
 160 </p>
 161
 162 <p>
 163 <a href="http://www.ticalc.org/archives/files/fileinfo/361/36173.html"
 164 target="_parent">ClosedGL</a> is an OpenGL subset library for TI
 165 graphing calculators.
 166 </p>
 167
 168 <p>
 169 There may be other open OpenGL implementations, but Mesa is the most
 170 popular 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
 186 has Mesa packages (like RPM or DEB) which you can easily install.
 187 </a></p>
 188
 189
 190 <h2><a name="part2">2.2 Running <code>configure; make</code> doesn't Work</a></h2>
 191 <p>
 192 Mesa no longer supports GNU autoconf/automake.  Why?
 193 <ul>
 194 <li>It seemed to seldom work on anything but Linux
 195 <li>The config files were hard to maintain and hard to understand
 196 <li>libtool caused a lot of grief
 197 </ul>
 198
 199 <p>
 200 Now Mesa again uses a conventional Makefile system (as it did originally).
 201 Basically, each Makefile in the tree includes one of the configuration
 202 files from the config/ directory.
 203 The config files specify all the variables for a variety of popular systems.
 204 </p>
 205
 206
 207 <h2><a name="part2">2.3 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2>
 208 <p>
 209 <a name="part2">You're application is written in IRIS GL, not OpenGL.
 210 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 211 entirely.
 212 Mesa's not the solution.
 213 </a></p>
 214
 215
 216 <h2><a name="part2">2.4 Where is the GLUT library?</a></h2>
 217 <p>
 218 <a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaGLUT-x.y.z.tar.gz file.
 219 If you don't already have GLUT installed, you should grab the MesaGLUT
 220 package and compile it with the rest of Mesa.
 221 </a></p>
 222
 223
 224
 225 <h2><a name="part2">2.5 What's the proper place for the libraries and headers?</a></h2>
 226 <p>
 227 <a name="part2">On Linux-based systems you'll want to follow the
 228 </a><a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html"
 229 target="_parent">Linux ABI</a> standard.
 230 Basically you'll want the following:
 231 </p>
 232 <ul>
 233 <li>/usr/include/GL/gl.h - the main OpenGL header
 234 </li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
 235 </li><li>/usr/include/GL/glx.h - the OpenGL GLX header
 236 </li><li>/usr/include/GL/glext.h - the OpenGL extensions header
 237 </li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
 238 </li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
 239 </li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
 240 </li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
 241 </li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library.  xyz denotes the
 242 Mesa version number.
 243 </li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1
 244 </li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz
 245 </li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library.  xyz denotes the Mesa
 246 version number.
 247 </li></ul>
 248 <p>
 249 After installing XFree86/X.org and the DRI drivers, some of these files
 250 may be symlinks into the /usr/X11R6/ tree.
 251 </p>
 252 <p>
 253 The old-style Makefile system doesn't install the Mesa libraries; it's
 254 up to you to copy them (and the headers) to the right place.
 255 </p>
 256 <p>
 257 The GLUT header and library should go in the same directories.
 258 </p>
 259 <br>
 260 <br>
 261
 262
 263 <a name="part3">
 264 </a><h1><a name="part3">3. Runtime / Rendering Problems</a></h1>
 265
 266 <h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2>
 267 <p>
 268 <a name="part3">Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any
 269 support for hardware acceleration (with the exception of the 3DFX Voodoo
 270 driver).
 271 </a></p>
 272 <p>
 273 <a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
 274 for your particular hardware.
 275 </a></p>
 276 <p>
 277 <a name="part3">You can run the <code>glxinfo</code> program to learn about your OpenGL
 278 library.
 279 Look for the GL_VENDOR and GL_RENDERER values.
 280 That will identify who's OpenGL library you're using and what sort of
 281 hardware it has detected.
 282 </a></p>
 283 <p>
 284 <a name="part3">If your DRI-based driver isn't working, go to the
 285 </a><a href="http://dri.sf.net/" target="_parent">DRI website</a> for trouble-shooting information.
 286 </p>
 287
 288
 289 <h2>3.2 I'm seeing errors in depth (Z) buffering.  Why?</h2>
 290 <p>
 291 Make sure the ratio of the far to near clipping planes isn't too great.
 292 Look
 293 <a href="http://www.opengl.org/resources/faq/technical/depthbuffer.htm#0040"
 294 target="_parent"> here</a> for details.
 295 </p>
 296 <p>
 297 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 298 to clear than a 32-bit buffer but not as accurate.
 299 If you need a deeper you can modify the parameters to
 300 <code> glXChooseVisual</code> in your code.
 301 </p>
 302
 303
 304 <h2>3.3 Why Isn't depth buffering working at all?</h2>
 305 <p>
 306 Be sure you're requesting a depth buffered-visual.  If you set the MESA_DEBUG
 307 environment variable it will warn you about trying to enable depth testing
 308 when you don't have a depth buffer.
 309 </p>
 310 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 311 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 312 called with a non-zero value for GLX_DEPTH_SIZE.
 313 </p>
 314 <p>This discussion applies to stencil buffers, accumulation buffers and
 315 alpha channels too.
 316 </p>
 317
 318
 319 <h2>3.4 Why does glGetString() always return NULL?</h2>
 320 <p>
 321 Be sure you have an active/current OpenGL rendering context before
 322 calling glGetString.
 323 </p>
 324
 325
 326 <h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
 327 <p>
 328 If you're trying to draw a filled region by using GL_POINTS or GL_LINES
 329 and seeing holes or gaps it's because of a float-to-int rounding problem.
 330 But this is not a bug.
 331 See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
 332 Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
 333 will fix the problem.
 334 </p>
 335
 336 <br>
 337 <br>
 338
 339
 340 <a name="part4">
 341 </a><h1><a name="part4">4. Developer Questions</a></h1>
 342
 343 <h2>4.1 How can I contribute?</a></h2>
 344 <p>
 345 First, join the <a href="http://www.mesa3d.org/lists.html">Mesa3d-dev
 346 mailing list</a>.
 347 That's where Mesa development is discussed.
 348 </p>
 349 <p>
 350 The <a href="http://www.opengl.org/documentation" target="_parent">
 351 OpenGL Specification</a> is the bible for OpenGL implemention work.
 352 You should read it.
 353 </p>
 354 <p>Most of the Mesa development work involves implementing new OpenGL
 355 extensions, writing hardware drivers (for the DRI), and code optimization.
 356 </p>
 357
 358 <h2>4.2 How do I write a new device driver?</h2>
 359 <p>
 360 Unfortunately, writing a device driver isn't easy.
 361 It requires detailed understanding of OpenGL, the Mesa code, and your
 362 target hardware/operating system.
 363 3D graphics are not simple.
 364 </p>
 365 <p>
 366 The best way to get started is to use an existing driver as your starting
 367 point.
 368 For a software driver, the X11 and OSMesa drivers are good examples.
 369 For a hardware driver, the Radeon and R200 DRI drivers are good examples.
 370 </p>
 371 <p>The DRI website has more information about writing hardware drivers.
 372 The process isn't well document because the Mesa driver interface changes
 373 over time, and we seldome have spare time for writing documentation.
 374 That being said, many people have managed to figure out the process.
 375 </p>
 376 <p>
 377 Joining the appropriate mailing lists and asking questions (and searching
 378 the archives) is a good way to get information.
 379 </p>
 380
 381
 382 <h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa?</h2>
 383 <p>
 384 The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a>
 385 indicates that there are intellectual property (IP) and/or patent issues
 386 to be dealt with.
 387 </p>
 388 <p>We've been unsucessful in getting a response from S3 (or whoever owns
 389 the IP nowadays) to indicate whether or not an open source project can
 390 implement the extension (specifically the compression/decompression
 391 algorithms).
 392 </p>
 393 <p>
 394 In the mean time, a 3rd party <a href=
 395 "http://homepage.hispeed.ch/rscheidegger/dri_experimental/s3tc_index.html"
 396 target="_parent">plug-in library</a> is available.
 397 </p>
 398
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