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   9 <h1>Mesa Frequently Asked Questions</h1>
  10 Last updated: 17 November 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 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
  84 <h2>1.4 What's the difference between"Stand-Alone" Mesa and the DRI drivers?</h2>
  85 <p>
  86 <em>Stand-alone Mesa</em> is the original incarnation of Mesa.
  87 On systems running the X Window System, it does all its rendering through
  88 the Xlib API.
  89 <ul>
  90 <li>The GLX API is supported, but it's really just an emulation of the
  91      real thing.
  92 <li>The GLX wire protocol is not supported and there's no OpenGL extension
  93     loaded by the X server.
  94 <li>There is no hardware acceleration.
  95 <li>The OpenGL library, libGL.so, contains everything (the programming API,
  96     the GLX functions and all the rendering code).
  97 </ul>
  98 </p>
  99 <p>
 100 Alternately, Mesa acts as the core for a number of OpenGL hardware drivers
 101 within the DRI (Direct Rendering Infrastructure):
 102 <ul>
 103 <li>The libGL.so library provides the GL and GLX API functions, a GLX
 104     protocol encoder, and a device driver loader.
 105 <li>The device driver modules (such as r200_dri.so) contain a built-in
 106     copy of the core Mesa code.
 107 <li>The X server loads the GLX module.
 108     The GLX module decodes incoming GLX protocol and dispatches the commands
 109     to a rendering module.
 110     For the DRI, this module is basically a software Mesa renderer.
 111 </ul>
 112
 113
 114
 115 <h2>1.5 How do I upgrade my DRI installation to use a new Mesa release?</h2>
 116 <p>
 117 You don't!  A copy of the Mesa source code lives inside the XFree86/DRI source
 118 tree and gets compiled into the individual DRI driver modules.
 119 If you try to install Mesa over an XFree86/DRI installation, you'll lose
 120 hardware rendering (because stand-alone Mesa's libGL.so is different than
 121 the XFree86 libGL.so).
 122 </p>
 123 <p>
 124 The DRI developers will incorporate the latest release of Mesa into the
 125 DRI drivers when the time is right.
 126 </p>
 127 <p>
 128 To upgrade, either look for a new release of <a href="http://www.xfree86.org"
 129 target="_parent">XFree86</a> or visit the
 130 <a href="http://dri.sf.net" target="_parent">DRI website</a> to see
 131 if there's newer drivers.
 132 </p>
 133
 134
 135 <h2>1.6 Are there other open-source implementations of OpenGL?</h2>
 136 <p>
 137 Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html"
 138 target="_parent">
 139 OpenGL Sample Implemenation (SI)</a> is available.
 140 The SI was written during the time that OpenGL was originally designed.
 141 Unfortunately, development of the SI has stagnated.
 142 Mesa is much more up to date with modern features and extensions.
 143 </p>
 144
 145 <p>
 146 <a href="http://ogl-es.sourceforge.net" target="_parent">Vincent</a> is
 147 an open-source implementation of OpenGL ES for mobile devices.
 148
 149 <p>
 150 <a href="http://www.dsbox.com/minigl.html" target="_parent">miniGL</a>
 151 is a subset of OpenGL for PalmOS devices.
 152
 153 <p>
 154 <a href="http://fabrice.bellard.free.fr/TinyGL/"
 155 target="_parent">TinyGL</a> is a subset of OpenGL.
 156 </p>
 157
 158 <p>
 159 <a href="http://softgl.studierstube.org/" target="_parent">SoftGL</a>
 160 is an OpenGL subset for mobile devices.
 161 </p>
 162
 163 <p>
 164 <a href="http://chromium.sourceforge.net/" target="_parent">Chromium</a>
 165 isn't a conventional OpenGL implementation (it's layered upon OpenGL),
 166 but it does export the OpenGL API.  It allows tiled rendering, sort-last
 167 rendering, etc.
 168 </p>
 169
 170 <p>
 171 There may be other open OpenGL implementations, but Mesa is the most
 172 popular and feature-complete.
 173 </p>
 174
 175
 176
 177 <br>
 178 <br>
 179
 180
 181 <a name="part2">
 182 </a><h1><a name="part2">2. Compilation and Installation Problems</a></h1>
 183
 184
 185 <h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2>
 186 <p>
 187 <a name="part2">If you're using a Linux-based system, your distro CD most likely already
 188 has Mesa packages (like RPM or DEB) which you can easily install.
 189 </a></p>
 190
 191
 192 <h2><a name="part2">2.2 Running <code>configure; make</code> doesn't Work</a></h2>
 193 <p>
 194 Mesa no longer supports GNU autoconf/automake.  Why?
 195 <ul>
 196 <li>It seemed to seldom work on anything but Linux
 197 <li>The config files were hard to maintain and hard to understand
 198 <li>libtool caused a lot of grief
 199 </ul>
 200
 201 <p>
 202 Now, Mesa again uses a conventional Makefile system (as it did originally).
 203 Basically, each Makefile in the tree includes one of the configuration
 204 files from the config/ directory.
 205 The config files specify all the variables for a variety of popular systems.
 206 </p>
 207
 208
 209 <h2><a name="part2">2.3 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2>
 210 <p>
 211 <a name="part2">You're application is written in IRIS GL, not OpenGL.
 212 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 213 entirely.
 214 Mesa's not the solution.
 215 </a></p>
 216
 217
 218 <h2><a name="part2">2.4 Where is the GLUT library?</a></h2>
 219 <p>
 220 <a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaDemos-x.y.z.tar.gz file.
 221 If you don't already have GLUT installed, you should grab the MesaDemos
 222 package and unpack it before compiling Mesa.
 223 </a></p>
 224
 225
 226
 227 <h2><a name="part2">2.5 What's the proper place for the libraries and headers?</a></h2>
 228 <p>
 229 <a name="part2">On Linux-based systems you'll want to follow the
 230 </a><a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html"
 231 target="_parent">Linux ABI</a> standard.
 232 Basically you'll want the following:
 233 </p>
 234 <ul>
 235 <li>/usr/include/GL/gl.h - the main OpenGL header
 236 </li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
 237 </li><li>/usr/include/GL/glx.h - the OpenGL GLX header
 238 </li><li>/usr/include/GL/glext.h - the OpenGL extensions header
 239 </li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
 240 </li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
 241 </li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
 242 </li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
 243 </li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library.  xyz denotes the
 244 Mesa version number.
 245 </li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1
 246 </li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz
 247 </li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library.  xyz denotes the Mesa
 248 version number.
 249 </li></ul>
 250 <p>
 251 After installing XFree86 and the DRI drivers, some of these files
 252 may be symlinks into the /usr/X11R6/ tree.
 253 </p>
 254 <p>
 255 The old-style Makefile system doesn't install the Mesa libraries; it's
 256 up to you to copy them (and the headers) to the right place.
 257 </p>
 258 <p>
 259 The GLUT header and library should go in the same directories.
 260 </p>
 261 <br>
 262 <br>
 263
 264
 265 <a name="part3">
 266 </a><h1><a name="part3">3. Runtime / Rendering Problems</a></h1>
 267
 268 <h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2>
 269 <p>
 270 <a name="part3">Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any
 271 support for hardware acceleration (with the exception of the 3DFX Voodoo
 272 driver).
 273 </a></p>
 274 <p>
 275 <a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
 276 for your particular hardware.
 277 </a></p>
 278 <p>
 279 <a name="part3">You can run the <code>glxinfo</code> program to learn about your OpenGL
 280 library.
 281 Look for the GL_VENDOR and GL_RENDERER values.
 282 That will identify who's OpenGL library you're using and what sort of
 283 hardware it has detected.
 284 </a></p>
 285 <p>
 286 <a name="part3">If your DRI-based driver isn't working, go to the
 287 </a><a href="http://dri.sf.net/" target="_parent">DRI website</a> for trouble-shooting information.
 288 </p>
 289
 290
 291 <h2>3.2 I'm seeing errors in depth (Z) buffering.  Why?</h2>
 292 <p>
 293 Make sure the ratio of the far to near clipping planes isn't too great.
 294 Look
 295 <a href="http://www.sgi.com/software/opengl/advanced97/notes/node18.html"
 296 target="_parent">
 297 here</a> for details.
 298 </p>
 299 <p>
 300 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 301 to clear than a 32-bit buffer but not as accurate.
 302 If you need a deeper you can modify the parameters to
 303 <code> glXChooseVisual</code> in your code.
 304 </p>
 305
 306
 307 <h2>3.3 Why Isn't depth buffering working at all?</h2>
 308 <p>
 309 Be sure you're requesting a depth buffered-visual.  If you set the MESA_DEBUG
 310 environment variable it will warn you about trying to enable depth testing
 311 when you don't have a depth buffer.
 312 </p>
 313 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 314 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 315 called with a non-zero value for GLX_DEPTH_SIZE.
 316 </p>
 317 <p>This discussion applies to stencil buffers, accumulation buffers and
 318 alpha channels too.
 319 </p>
 320
 321
 322 <h2>3.4 Why does glGetString() always return NULL?</h2>
 323 <p>
 324 Be sure you have an active/current OpenGL rendering context before
 325 calling glGetString.
 326 </p>
 327
 328
 329 <h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
 330 <p>
 331 If you're trying to draw a filled region by using GL_POINTS or GL_LINES
 332 and seeing holes or gaps it's because of a float-to-int rounding problem.
 333 But this is not a bug.
 334 See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
 335 Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
 336 will fix the problem.
 337 </p>
 338
 339 <br>
 340 <br>
 341
 342
 343 <a name="part4">
 344 </a><h1><a name="part4">4. Developer Questions</a></h1>
 345
 346 <h2><a name="part4">4.1 How can I contribute?</a></h2>
 347 <p>
 348 <a name="part4">First, join the Mesa3d-dev mailing list.  That's where Mesa development
 349 is discussed.
 350 </a></p>
 351 <p>
 352 <a name="part4">The </a><a href="http://www.opengl.org/developers/documentation/specs.html" target="_parent">
 353 OpenGL Specification</a> is the bible for OpenGL implemention work.
 354 You should read it.
 355 </p>
 356 <p>Most of the Mesa development work involves implementing new OpenGL
 357 extensions, writing hardware drivers (for the DRI), and code optimization.
 358 </p>
 359
 360 <h2>4.2 How do I write a new device driver?</h2>
 361 <p>
 362 Unfortunately, writing a device driver isn't easy.
 363 It requires detailed understanding of OpenGL, the Mesa code, and your
 364 target hardware/operating system.
 365 3D graphics are not simple.
 366 </p>
 367 <p>
 368 The best way to get started is to use an existing driver as your starting
 369 point.
 370 For a software driver, the X11 and OSMesa drivers are good examples.
 371 For a hardware driver, the Radeon and R200 DRI drivers are good examples.
 372 </p>
 373 <p>The DRI website has more information about writing hardware drivers.
 374 The process isn't well document because the Mesa driver interface changes
 375 over time, and we seldome have spare time for writing documentation.
 376 That being said, many people have managed to figure out the process.
 377 </p>
 378 <p>
 379 Joining the appropriate mailing lists and asking questions (and searching
 380 the archives) is a good way to get information.
 381 </p>
 382
 383
 384 <h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa and/or the DRI drivers?</h2>
 385 <p>
 386 The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a>
 387 indicates that there are intellectual property (IP) and/or patent issues
 388 to be dealt with.
 389 </p>
 390 <p>We've been unsucessful in getting a response from S3 (or whoever owns
 391 the IP nowadays) to indicate whether or not an open source project can
 392 implement the extension (specifically the compression/decompression
 393 algorithms).
 394 </p>
 395 <p>
 396 Until we can get official permission to do so, this extension will not
 397 be implemented in Mesa.
 398 </p>
 399
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