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   9 <h1>Mesa Frequently Asked Questions</h1>
  10 Last updated: 27 April 2004
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  12
  13 <br>
  14 <br>
  15 <h2>Index</h2>
  16 <a href="#part1">1. High-level Questions and Answers</a>
  17 <br>
  18 <a href="#part2">2. Compilation and Installation Problems</a>
  19 <br>
  20 <a href="#part3">3. Runtime / Rendering Problems</a>
  21 <br>
  22 <a href="#part4">4. Developer Questions</a>
  23 <br>
  24 <br>
  25 <br>
  26
  27
  28
  29 <a name="part1">
  30 </a><h1><a name="part1">1. High-level Questions and Answers</a></h1>
  31
  32 <h2><a name="part1">1.1 What is Mesa?</a></h2>
  33 <p>
  34 <a name="part1">Mesa is an open-source implementation of the OpenGL specification.
  35 OpenGL is a programming library for writing interactive 3D applications.
  36 See the </a><a href="http://www.opengl.org/">OpenGL website</a> for more
  37 information.
  38 </p>
  39 <p>
  40 Mesa 5.x supports the OpenGL 1.4 specification.
  41 </p>
  42
  43
  44 <h2>1.2 Does Mesa support/use graphics hardware?</h2>
  45 <p>
  46 Yes.  Specifically, Mesa serves as the OpenGL core for the open-source
  47 XFree86/DRI OpenGL drivers.  See the <a href="http://dri.sf.net/">DRI
  48 website</a> for more information.
  49 </p>
  50 <p>
  51 There have been other hardware drivers for Mesa over the years (such as
  52 the 3Dfx Glide/Voodoo driver, an old S3 driver, etc) but the DRI drivers
  53 are the modern ones.
  54 </p>
  55
  56 <h2>1.3 What purpose does Mesa (software-based rendering) serve today?</h2>
  57 <p>
  58 Hardware-accelerated OpenGL implementations are available for most popular
  59 operating systems today.
  60 Still, Mesa serves at least these purposes:
  61 </p>
  62 <ul>
  63 <li>Mesa is used as the core of the open-source XFree86/DRI hardware drivers.
  64 </li>
  65 <li>Mesa is quite portable and allows OpenGL to be used on systems
  66     that have no other OpenGL solution.
  67 </li>
  68 <li>Software rendering with Mesa serves as a reference for validating the
  69     hardware drivers.
  70 </li>
  71 <li>A software implementation of OpenGL is useful for experimentation,
  72     such as testing new rendering techniques.
  73 </li>
  74 <li>Mesa can render images with deep color channels: 16-bit integer
  75     and 32-bit floating point color channels are supported.
  76     This capability is only now appearing in hardware.
  77 </li>
  78 <li>Mesa's internal limits (max lights, clip planes, texture size, etc) can be
  79     changed for special needs (hardware limits are hard to overcome).
  80 </li>
  81 </ul>
  82
  83 <h2>1.4 How do I upgrade my DRI installation to use a new Mesa release?</h2>
  84 <p>
  85 You don't!  A copy of the Mesa source code lives inside the XFree86/DRI source
  86 tree and gets compiled into the individual DRI driver modules.
  87 If you try to install Mesa over an XFree86/DRI installation, you'll lose
  88 hardware rendering (because stand-alone Mesa's libGL.so is different than
  89 the XFree86 libGL.so).
  90 </p>
  91 <p>
  92 The DRI developers will incorporate the latest release of Mesa into the
  93 DRI drivers when the time is right.
  94 </p>
  95 <p>
  96 To upgrade, either look for a new release of <a href="http://www.xfree86.org"
  97 target="_parent">XFree86</a> or visit the
  98 <a href="http://dri.sf.net" target="_parent">DRI website</a> to see
  99 if there's newer drivers.
 100 </p>
 101
 102
 103 <h2>1.5 Are there other open-source implementations of OpenGL?</h2>
 104 <p>
 105 Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html"
 106 target="_parent">
 107 OpenGL Sample Implemenation (SI)</a> is available.
 108 The SI was written during the time that OpenGL was originally designed.
 109 Unfortunately, development of the SI has stagnated.
 110 Mesa is much more up to date with modern features and extensions.
 111 </p>
 112
 113 <p>
 114 <a href="http://ogl-es.sourceforge.net" target="_parent">Vincent</a> is
 115 an open-source implementation of OpenGL ES for mobile devices.
 116
 117 <p>
 118 <a href="http://www.dsbox.com/minigl.html" target="_parent">miniGL</a>
 119 is a subset of OpenGL for PalmOS devices.
 120
 121 <p>
 122 <a href="http://fabrice.bellard.free.fr/TinyGL/"
 123 target="_parent">TinyGL</a> is a subset of OpenGL.
 124 </p>
 125
 126 <p>
 127 <a href="http://softgl.studierstube.org/" target="_parent">SoftGL</a>
 128 is an OpenGL subset for mobile devices.
 129 </p>
 130
 131 <p>
 132 <a href="http://chromium.sourceforge.net/" target="_parent">Chromium</a>
 133 isn't a conventional OpenGL implementation (it's layered upon OpenGL),
 134 but it does export the OpenGL API.  It allows tiled rendering, sort-last
 135 rendering, etc.
 136 </p>
 137
 138
 139 <p>
 140 There may be other open OpenGL implementations, but Mesa is the most
 141 popular and feature-complete.
 142 </p>
 143
 144 <br>
 145 <br>
 146
 147
 148 <a name="part2">
 149 </a><h1><a name="part2">2. Compilation and Installation Problems</a></h1>
 150
 151
 152 <h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2>
 153 <p>
 154 <a name="part2">If you're using a Linux-based system, your distro CD most likely already
 155 has Mesa packages (like RPM or DEB) which you can easily install.
 156 </a></p>
 157
 158
 159 <h2><a name="part2">2.2 Running <code>configure; make</code> Doesn't Work</a></h2>
 160 <p>
 161 <a name="part2">Unfortunately, the GNU autoconf/automake/libtool system doesn't seem to work
 162 too well on non GNU/Linux systems, even after installing gmake, gcc, etc.
 163 For that reason, Mesa's <b>old-style</b> makefile system is still included.
 164 The old-style system uses good old traditional Makefiles.  Try the following:
 165 </a></p><pre><a name="part2">  cd Mesa-x.y.z
 166   cp Makefile.X11 Makefile
 167   make
 168 </a></pre>
 169 <a name="part2">You'll see a list of system configurations from which to choose.
 170 For example:
 171 </a><pre><a name="part2">  make linux-x86
 172 </a></pre>
 173 <p>
 174 <a name="part2">If you're experienced with GNU autoconf/automake/libtool and think you can help
 175 with maintence, contact the Mesa developers.
 176 FYI, the Mesa developers generally don't use the autoconf/automake system.
 177 We're especially annoyed with the fact that a +5000-line script (libtool)
 178 is needed to make shared libraries (ugh).
 179 </a></p>
 180
 181 <h2><a name="part2">2.3 Mesa still doesn't compile</a></h2>
 182 <p>
 183 <a name="part2">If the old-style Makefile system doesn't work either, make sure you have
 184 the most recent version of Mesa.
 185 Otherwise, file a bug report or post to the Mesa3d-users mailing list.
 186 Give as much info as possible when describing your problem.
 187 </a></p>
 188
 189
 190 <h2><a name="part2">2.4 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.
 193 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 194 entirely.
 195 Mesa's not the solution.
 196 </a></p>
 197
 198
 199 <h2><a name="part2">2.5 Where is the GLUT library?</a></h2>
 200 <p>
 201 <a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaDemos-x.y.z.tar.gz file.
 202 If you don't already have GLUT installed, you should grab the MesaDemos
 203 package and unpack it before compiling Mesa.
 204 </a></p>
 205
 206
 207
 208 <h2><a name="part2">2.6 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"
 212 target="_parent">Linux ABI</a> standard.
 213 Basically 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
 225 Mesa 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
 229 version number.
 230 </li></ul>
 231 <p>
 232 After installing XFree86 and the DRI drivers, some of these files
 233 may be symlinks into the /usr/X11R6/ tree.
 234 </p>
 235 <p>
 236 The old-style Makefile system doesn't install the Mesa libraries; it's
 237 up to you to copy them (and the headers) to the right place.
 238 </p>
 239 <p>
 240 The 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
 252 support for hardware acceleration (with the exception of the 3DFX Voodoo
 253 driver).
 254 </a></p>
 255 <p>
 256 <a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
 257 for 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
 261 library.
 262 Look for the GL_VENDOR and GL_RENDERER values.
 263 That will identify who's OpenGL library you're using and what sort of
 264 hardware 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>
 274 Make sure the ratio of the far to near clipping planes isn't too great.
 275 Look
 276 <a href="http://www.sgi.com/software/opengl/advanced97/notes/node18.html"
 277 target="_parent">
 278 here</a> for details.
 279 </p>
 280 <p>
 281 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 282 to clear than a 32-bit buffer but not as accurate.
 283 If you need a deeper you can modify the parameters to
 284 <code> glXChooseVisual</code> in your code.
 285 </p>
 286
 287
 288 <h2>3.3 Why Isn't depth buffering working at all?</h2>
 289 <p>
 290 Be sure you're requesting a depth buffered-visual.  If you set the MESA_DEBUG
 291 environment variable it will warn you about trying to enable depth testing
 292 when you don't have a depth buffer.
 293 </p>
 294 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 295 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 296 called with a non-zero value for GLX_DEPTH_SIZE.
 297 </p>
 298 <p>This discussion applies to stencil buffers, accumulation buffers and
 299 alpha channels too.
 300 </p>
 301
 302
 303 <h2>3.4 Why does glGetString() always return NULL?</h2>
 304 <p>
 305 Be sure you have an active/current OpenGL rendering context before
 306 calling glGetString.
 307 </p>
 308
 309
 310 <h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
 311 <p>
 312 If you're trying to draw a filled region by using GL_POINTS or GL_LINES
 313 and seeing holes or gaps it's because of a float-to-int rounding problem.
 314 But this is not a bug.
 315 See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
 316 Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
 317 will fix the problem.
 318 </p>
 319
 320 <br>
 321 <br>
 322
 323
 324 <a name="part4">
 325 </a><h1><a name="part4">4. Developer Questions</a></h1>
 326
 327 <h2><a name="part4">4.1 How can I contribute?</a></h2>
 328 <p>
 329 <a name="part4">First, join the Mesa3d-dev mailing list.  That's where Mesa development
 330 is discussed.
 331 </a></p>
 332 <p>
 333 <a name="part4">The </a><a href="http://www.opengl.org/developers/documentation/specs.html" target="_parent">
 334 OpenGL Specification</a> is the bible for OpenGL implemention work.
 335 You should read it.
 336 </p>
 337 <p>Most of the Mesa development work involves implementing new OpenGL
 338 extensions, writing hardware drivers (for the DRI), and code optimization.
 339 </p>
 340
 341 <h2>4.2 How do I write a new device driver?</h2>
 342 <p>
 343 Unfortunately, writing a device driver isn't easy.
 344 It requires detailed understanding of OpenGL, the Mesa code, and your
 345 target hardware/operating system.
 346 3D graphics are not simple.
 347 </p>
 348 <p>
 349 The best way to get started is to use an existing driver as your starting
 350 point.
 351 For a software driver, the X11 and OSMesa drivers are good examples.
 352 For a hardware driver, the Radeon and R200 DRI drivers are good examples.
 353 </p>
 354 <p>The DRI website has more information about writing hardware drivers.
 355 The process isn't well document because the Mesa driver interface changes
 356 over time, and we seldome have spare time for writing documentation.
 357 That being said, many people have managed to figure out the process.
 358 </p>
 359 <p>
 360 Joining the appropriate mailing lists and asking questions (and searching
 361 the archives) is a good way to get information.
 362 </p>
 363
 364
 365 <h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa and/or the DRI drivers?</h2>
 366 <p>
 367 The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a>
 368 indicates that there are intellectual property (IP) and/or patent issues
 369 to be dealt with.
 370 </p>
 371 <p>We've been unsucessful in getting a response from S3 (or whoever owns
 372 the IP nowadays) to indicate whether or not an open source project can
 373 implement the extension (specifically the compression/decompression
 374 algorithms).
 375 </p>
 376 <p>
 377 Until we can get official permission to do so, this extension will not
 378 be implemented in Mesa.
 379 </p>
 380
 381
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