docs/faq.html

   1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
   2 <html lang="en">
   3 <head>
   4   <meta http-equiv="content-type" content="text/html; charset=utf-8">
   5   <title>Mesa FAQ</title>
   6   <link rel="stylesheet" type="text/css" href="mesa.css">
   7 </head>
   8 <body>
   9
  10 <center>
  11 <h1>Mesa Frequently Asked Questions</h1>
  12 Last updated: 21 August 2006
  13 </center>
  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 <h1 id="part1">1. High-level Questions and Answers</h1>
  32
  33 <h2>1.1 What is Mesa?</h2>
  34 <p>
  35 Mesa is an open-source implementation of the OpenGL specification.
  36 OpenGL is a programming library for writing interactive 3D applications.
  37 See the <a href="http://www.opengl.org/">OpenGL website</a> for more
  38 information.
  39 </p>
  40 <p>
  41 Mesa 6.x supports the OpenGL 1.5 specification.
  42 </p>
  43
  44
  45 <h2>1.2 Does Mesa support/use graphics hardware?</h2>
  46 <p>
  47 Yes.  Specifically, Mesa serves as the OpenGL core for the open-source DRI
  48 drivers for XFree86/X.org.  See the <a href="http://dri.freedesktop.org/">DRI
  49 website</a> for more information.
  50 </p>
  51 <p>
  52 There have been other hardware drivers for Mesa over the years (such as
  53 the 3Dfx Glide/Voodoo driver, an old S3 driver, etc) but the DRI drivers
  54 are the modern ones.
  55 </p>
  56
  57 <h2>1.3 What purpose does Mesa serve today?</h2>
  58 <p>
  59 Hardware-accelerated OpenGL implementations are available for most popular
  60 operating systems today.
  61 Still, Mesa serves at least these purposes:
  62 </p>
  63 <ul>
  64 <li>Mesa is used as the core of the open-source XFree86/X.org DRI
  65     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 </p>
  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 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 This wasn't easy in the past.
 120 Now, the DRI drivers are included in the Mesa tree and can be compiled
 121 separately from the X server.
 122 Just follow the Mesa <a href="install.html">compilation instructions</a>.
 123 </p>
 124
 125
 126 <h2>1.6 Are there other open-source implementations of OpenGL?</h2>
 127 <p>
 128 Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html"
 129 target="_parent">
 130 OpenGL Sample Implemenation (SI)</a> is available.
 131 The SI was written during the time that OpenGL was originally designed.
 132 Unfortunately, development of the SI has stagnated.
 133 Mesa is much more up to date with modern features and extensions.
 134 </p>
 135
 136 <p>
 137 <a href="http://ogl-es.sourceforge.net" target="_parent">Vincent</a> is
 138 an open-source implementation of OpenGL ES for mobile devices.
 139
 140 <p>
 141 <a href="http://www.dsbox.com/minigl.html" target="_parent">miniGL</a>
 142 is a subset of OpenGL for PalmOS devices.
 143
 144 <p>
 145 <a href="http://fabrice.bellard.free.fr/TinyGL/"
 146 target="_parent">TinyGL</a> is a subset of OpenGL.
 147 </p>
 148
 149 <p>
 150 <a href="http://softgl.studierstube.org/" target="_parent">SoftGL</a>
 151 is an OpenGL subset for mobile devices.
 152 </p>
 153
 154 <p>
 155 <a href="http://chromium.sourceforge.net/" target="_parent">Chromium</a>
 156 isn't a conventional OpenGL implementation (it's layered upon OpenGL),
 157 but it does export the OpenGL API.  It allows tiled rendering, sort-last
 158 rendering, etc.
 159 </p>
 160
 161 <p>
 162 <a href="http://www.ticalc.org/archives/files/fileinfo/361/36173.html"
 163 target="_parent">ClosedGL</a> is an OpenGL subset library for TI
 164 graphing calculators.
 165 </p>
 166
 167 <p>
 168 There may be other open OpenGL implementations, but Mesa is the most
 169 popular and feature-complete.
 170 </p>
 171
 172
 173
 174 <br>
 175 <br>
 176
 177
 178 <h1 id="part2">2. Compilation and Installation Problems</h1>
 179
 180
 181 <h2>2.1 What's the easiest way to install Mesa?</h2>
 182 <p>
 183 If you're using a Linux-based system, your distro CD most likely already
 184 has Mesa packages (like RPM or DEB) which you can easily install.
 185 </p>
 186
 187
 188 <h2>2.2 I get undefined symbols such as bgnpolygon, v3f, etc...</h2>
 189 <p>
 190 You're application is written in IRIS GL, not OpenGL.
 191 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 192 entirely.
 193 Mesa's not the solution.
 194 </p>
 195
 196
 197 <h2>2.3 Where is the GLUT library?</h2>
 198 <p>
 199 GLUT (OpenGL Utility Toolkit) is no longer in the separate MesaGLUT-x.y.z.tar.gz file.
 200 If you don't already have GLUT installed, you should grab
 201 <a href="http://freeglut.sourceforge.net/">freeglut</a>.
 202 </p>
 203
 204
 205 <h2>2.4 Where is the GLw library?</h2>
 206 <p>
 207 GLw (OpenGL widget library) is now available from a separate <a href="http://cgit.freedesktop.org/mesa/glw/">git repository</a>.  Unless you're using very old Xt/Motif applications with OpenGL, you shouldn't need it.
 208 </p>
 209
 210
 211 <h2>2.5 What's the proper place for the libraries and headers?</h2>
 212 <p>
 213 On Linux-based systems you'll want to follow the
 214 <a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html"
 215 target="_parent">Linux ABI</a> standard.
 216 Basically you'll want the following:
 217 </p>
 218 <ul>
 219 <li>/usr/include/GL/gl.h - the main OpenGL header
 220 </li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
 221 </li><li>/usr/include/GL/glx.h - the OpenGL GLX header
 222 </li><li>/usr/include/GL/glext.h - the OpenGL extensions header
 223 </li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
 224 </li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
 225 </li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
 226 </li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
 227 </li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library.  xyz denotes the
 228 Mesa version number.
 229 </li></ul>
 230 <p>
 231 After installing XFree86/X.org and the DRI drivers, some of these files
 232 may be symlinks into the /usr/X11R6/ tree.
 233 </p>
 234 <p>
 235 The old-style Makefile system doesn't install the Mesa libraries; it's
 236 up to you to copy them (and the headers) to the right place.
 237 </p>
 238 <p>
 239 The GLUT header and library should go in the same directories.
 240 </p>
 241 <br>
 242 <br>
 243
 244
 245 <h1 id="part3">3. Runtime / Rendering Problems</h1>
 246
 247 <h2>3.1 Rendering is slow / why isn't my graphics hardware being used?</h2>
 248 <p>
 249 Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any
 250 support for hardware acceleration (with the exception of the 3DFX Voodoo
 251 driver).
 252 </p>
 253 <p>
 254 What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
 255 for your particular hardware.
 256 </p>
 257 <p>
 258 You can run the <code>glxinfo</code> program to learn about your OpenGL
 259 library.
 260 Look for the GL_VENDOR and GL_RENDERER values.
 261 That will identify who's OpenGL library you're using and what sort of
 262 hardware it has detected.
 263 </p>
 264 <p>
 265 If your DRI-based driver isn't working, go to the
 266 <a href="http://dri.sf.net/" target="_parent">DRI website</a> for trouble-shooting information.
 267 </p>
 268
 269
 270 <h2>3.2 I'm seeing errors in depth (Z) buffering.  Why?</h2>
 271 <p>
 272 Make sure the ratio of the far to near clipping planes isn't too great.
 273 Look
 274 <a href="http://www.opengl.org/resources/faq/technical/depthbuffer.htm#0040"
 275 target="_parent"> here</a> for details.
 276 </p>
 277 <p>
 278 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 279 to clear than a 32-bit buffer but not as accurate.
 280 If you need a deeper you can modify the parameters to
 281 <code> glXChooseVisual</code> in your code.
 282 </p>
 283
 284
 285 <h2>3.3 Why Isn't depth buffering working at all?</h2>
 286 <p>
 287 Be sure you're requesting a depth buffered-visual.  If you set the MESA_DEBUG
 288 environment variable it will warn you about trying to enable depth testing
 289 when you don't have a depth buffer.
 290 </p>
 291 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 292 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 293 called with a non-zero value for GLX_DEPTH_SIZE.
 294 </p>
 295 <p>This discussion applies to stencil buffers, accumulation buffers and
 296 alpha channels too.
 297 </p>
 298
 299
 300 <h2>3.4 Why does glGetString() always return NULL?</h2>
 301 <p>
 302 Be sure you have an active/current OpenGL rendering context before
 303 calling glGetString.
 304 </p>
 305
 306
 307 <h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
 308 <p>
 309 If you're trying to draw a filled region by using GL_POINTS or GL_LINES
 310 and seeing holes or gaps it's because of a float-to-int rounding problem.
 311 But this is not a bug.
 312 See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
 313 Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
 314 will fix the problem.
 315 </p>
 316
 317 <h2>3.6 How can I change the maximum framebuffer size in Mesa's
 318 <tt>swrast</tt> backend?</h2>
 319 <p>
 320 These can be overridden by using the <tt>--with-max-width</tt> and
 321 <tt>--with-max-height</tt> options.  The two need not be equal.
 322 </p><p>
 323 Do note that Mesa uses these values to size some internal buffers,
 324 so increasing these sizes will cause Mesa to require additional
 325 memory.  Furthermore, increasing these limits beyond <tt>4096</tt>
 326 may introduce rasterization artifacts; see the leading comments in
 327 <tt>src/mesa/swrast/s_tritemp.h</tt>.
 328 </p>
 329
 330 <br>
 331 <br>
 332
 333
 334 <h1 id="part4">4. Developer Questions</h1>
 335
 336 <h2>4.1 How can I contribute?</h2>
 337 <p>
 338 First, join the <a href="http://www.mesa3d.org/lists.html">Mesa3d-dev
 339 mailing list</a>.
 340 That's where Mesa development is discussed.
 341 </p>
 342 <p>
 343 The <a href="http://www.opengl.org/documentation" target="_parent">
 344 OpenGL Specification</a> is the bible for OpenGL implemention work.
 345 You should read it.
 346 </p>
 347 <p>Most of the Mesa development work involves implementing new OpenGL
 348 extensions, writing hardware drivers (for the DRI), and code optimization.
 349 </p>
 350
 351 <h2>4.2 How do I write a new device driver?</h2>
 352 <p>
 353 Unfortunately, writing a device driver isn't easy.
 354 It requires detailed understanding of OpenGL, the Mesa code, and your
 355 target hardware/operating system.
 356 3D graphics are not simple.
 357 </p>
 358 <p>
 359 The best way to get started is to use an existing driver as your starting
 360 point.
 361 For a software driver, the X11 and OSMesa drivers are good examples.
 362 For a hardware driver, the Radeon and R200 DRI drivers are good examples.
 363 </p>
 364 <p>The DRI website has more information about writing hardware drivers.
 365 The process isn't well document because the Mesa driver interface changes
 366 over time, and we seldome have spare time for writing documentation.
 367 That being said, many people have managed to figure out the process.
 368 </p>
 369 <p>
 370 Joining the appropriate mailing lists and asking questions (and searching
 371 the archives) is a good way to get information.
 372 </p>
 373
 374
 375 <h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa?</h2>
 376 <p>
 377 The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a>
 378 indicates that there are intellectual property (IP) and/or patent issues
 379 to be dealt with.
 380 </p>
 381 <p>We've been unsucessful in getting a response from S3 (or whoever owns
 382 the IP nowadays) to indicate whether or not an open source project can
 383 implement the extension (specifically the compression/decompression
 384 algorithms).
 385 </p>
 386 <p>
 387 In the mean time, a 3rd party <a href=
 388 "http://dri.freedesktop.org/wiki/S3TC"
 389 target="_parent">plug-in library</a> is available.
 390 </p>
 391
 392 </body>
 393 </html>