workbench/libs/mesa/docs/faq.html

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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 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">2.3 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.
 202 If you don't already have GLUT installed, you should grab the MesaGLUT
 203 package 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"
 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/X.org 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.opengl.org/resources/faq/technical/depthbuffer.htm#0040"
 277 target="_parent"> here</a> for details.
 278 </p>
 279 <p>
 280 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 281 to clear than a 32-bit buffer but not as accurate.
 282 If 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>
 289 Be sure you're requesting a depth buffered-visual.  If you set the MESA_DEBUG
 290 environment variable it will warn you about trying to enable depth testing
 291 when you don't have a depth buffer.
 292 </p>
 293 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 294 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 295 called with a non-zero value for GLX_DEPTH_SIZE.
 296 </p>
 297 <p>This discussion applies to stencil buffers, accumulation buffers and
 298 alpha channels too.
 299 </p>
 300
 301
 302 <h2>3.4 Why does glGetString() always return NULL?</h2>
 303 <p>
 304 Be sure you have an active/current OpenGL rendering context before
 305 calling glGetString.
 306 </p>
 307
 308
 309 <h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
 310 <p>
 311 If you're trying to draw a filled region by using GL_POINTS or GL_LINES
 312 and seeing holes or gaps it's because of a float-to-int rounding problem.
 313 But this is not a bug.
 314 See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
 315 Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
 316 will 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>
 322 These 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>
 325 Do note that Mesa uses these values to size some internal buffers,
 326 so increasing these sizes will cause Mesa to require additional
 327 memory.  Furthermore, increasing these limits beyond <tt>4096</tt>
 328 may 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>
 341 First, join the <a href="http://www.mesa3d.org/lists.html">Mesa3d-dev
 342 mailing list</a>.
 343 That's where Mesa development is discussed.
 344 </p>
 345 <p>
 346 The <a href="http://www.opengl.org/documentation" target="_parent">
 347 OpenGL Specification</a> is the bible for OpenGL implemention work.
 348 You should read it.
 349 </p>
 350 <p>Most of the Mesa development work involves implementing new OpenGL
 351 extensions, 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>
 356 Unfortunately, writing a device driver isn't easy.
 357 It requires detailed understanding of OpenGL, the Mesa code, and your
 358 target hardware/operating system.
 359 3D graphics are not simple.
 360 </p>
 361 <p>
 362 The best way to get started is to use an existing driver as your starting
 363 point.
 364 For a software driver, the X11 and OSMesa drivers are good examples.
 365 For 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.
 368 The process isn't well document because the Mesa driver interface changes
 369 over time, and we seldome have spare time for writing documentation.
 370 That being said, many people have managed to figure out the process.
 371 </p>
 372 <p>
 373 Joining the appropriate mailing lists and asking questions (and searching
 374 the 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>
 380 The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a>
 381 indicates that there are intellectual property (IP) and/or patent issues
 382 to be dealt with.
 383 </p>
 384 <p>We've been unsucessful in getting a response from S3 (or whoever owns
 385 the IP nowadays) to indicate whether or not an open source project can
 386 implement the extension (specifically the compression/decompression
 387 algorithms).
 388 </p>
 389 <p>
 390 In the mean time, a 3rd party <a href=
 391 "http://homepage.hispeed.ch/rscheidegger/dri_experimental/s3tc_index.html"
 392 target="_parent">plug-in library</a> is available.
 393 </p>
 394
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