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   9 <h1>Mesa Frequently Asked Questions</h1>
  10 Last updated: 30 March 2003
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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
  96 <h2>1.5 Are there other open-source implementations of OpenGL?</h2>
  97 <p>
  98 Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html">
  99 OpenGL Sample Implemenation (SI)</a> is available.
 100 The SI was written during the time that OpenGL was originally designed.
 101 Unfortunately, development of the SI has stagnated.
 102 Mesa is much more up to date with modern features and extensions.
 103 </p>
 104 <p>
 105 <a href="http://www.dsbox.com/minigl.html">miniGL</a> is a subset of OpenGL
 106 for PalmOS devices.
 107
 108 <a href="http://fabrice.bellard.free.fr/TinyGL/">TinyGL</a> is another
 109 subset of OpenGL.
 110 </p>
 111 <p>
 112 There may be others but Mesa is the most popular and feature-complete.
 113 </p>
 114
 115 <br>
 116 <br>
 117
 118
 119 <a name="part2">
 120 </a><h1><a name="part2">2. Compilation and Installation Problems</a></h1>
 121
 122
 123 <h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2>
 124 <p>
 125 <a name="part2">If you're using a Linux-based system, your distro CD most likely already
 126 has Mesa packages (like RPM or DEB) which you can easily install.
 127 </a></p>
 128
 129
 130 <h2><a name="part2">2.2 Running <code>configure; make</code> Doesn't Work</a></h2>
 131 <p>
 132 <a name="part2">Unfortunately, the GNU autoconf/automake/libtool system doesn't seem to work
 133 too well on non GNU/Linux systems, even after installing gmake, gcc, etc.
 134 For that reason, Mesa's <b>old-style</b> makefile system is still included.
 135 The old-style system uses good old traditional Makefiles.  Try the following:
 136 </a></p><pre><a name="part2">  cd Mesa-x.y.z
 137   cp Makefile.X11 Makefile
 138   make
 139 </a></pre>
 140 <a name="part2">You'll see a list of system configurations from which to choose.
 141 For example:
 142 </a><pre><a name="part2">  make linux-x86
 143 </a></pre>
 144 <p>
 145 <a name="part2">If you're experienced with GNU autoconf/automake/libtool and think you can help
 146 with maintence, contact the Mesa developers.
 147 FYI, the Mesa developers generally don't use the autoconf/automake system.
 148 We're especially annoyed with the fact that a +5000-line script (libtool)
 149 is needed to make shared libraries (ugh).
 150 </a></p>
 151
 152 <h2><a name="part2">2.3 Mesa still doesn't compile</a></h2>
 153 <p>
 154 <a name="part2">If the old-style Makefile system doesn't work either, make sure you have
 155 the most recent version of Mesa.
 156 Otherwise, file a bug report or post to the Mesa3d-users mailing list.
 157 Give as much info as possible when describing your problem.
 158 </a></p>
 159
 160
 161 <h2><a name="part2">2.4 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2>
 162 <p>
 163 <a name="part2">You're application is written in IRIS GL, not OpenGL.
 164 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 165 entirely.
 166 Mesa's not the solution.
 167 </a></p>
 168
 169
 170 <h2><a name="part2">2.5 Where is the GLUT library?</a></h2>
 171 <p>
 172 <a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaDemos-x.y.z.tar.gz file.
 173 If you don't already have GLUT installed, you should grab the MesaDemos
 174 package and unpack it before compiling Mesa.
 175 </a></p>
 176
 177
 178
 179 <h2><a name="part2">2.6 What's the proper place for the libraries and headers?</a></h2>
 180 <p>
 181 <a name="part2">On Linux-based systems you'll want to follow the
 182 </a><a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html">Linux ABI</a>
 183 standard.
 184 Basically you'll want the following:
 185 </p>
 186 <ul>
 187 <li>/usr/include/GL/gl.h - the main OpenGL header
 188 </li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
 189 </li><li>/usr/include/GL/glx.h - the OpenGL GLX header
 190 </li><li>/usr/include/GL/glext.h - the OpenGL extensions header
 191 </li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
 192 </li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
 193 </li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
 194 </li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
 195 </li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library.  xyz denotes the
 196 Mesa version number.
 197 </li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1
 198 </li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz
 199 </li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library.  xyz denotes the Mesa
 200 version number.
 201 </li></ul>
 202 <p>
 203 After installing XFree86 and the DRI drivers, some of these files
 204 may be symlinks into the /usr/X11R6/ tree.
 205 </p>
 206 <p>
 207 The old-style Makefile system doesn't install the Mesa libraries; it's
 208 up to you to copy them (and the headers) to the right place.
 209 </p>
 210 <p>
 211 The GLUT header and library should go in the same directories.
 212 </p>
 213 <br>
 214 <br>
 215
 216
 217 <a name="part3">
 218 </a><h1><a name="part3">3. Runtime / Rendering Problems</a></h1>
 219
 220 <h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2>
 221 <p>
 222 <a name="part3">Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any
 223 support for hardware acceleration (with the exception of the 3DFX Voodoo
 224 driver).
 225 </a></p>
 226 <p>
 227 <a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
 228 for your particular hardware.
 229 </a></p>
 230 <p>
 231 <a name="part3">You can run the <code>glxinfo</code> program to learn about your OpenGL
 232 library.
 233 Look for the GL_VENDOR and GL_RENDERER values.
 234 That will identify who's OpenGL library you're using and what sort of
 235 hardware it has detected.
 236 </a></p>
 237 <p>
 238 <a name="part3">If your DRI-based driver isn't working, go to the
 239 </a><a href="http://dri.sf.net/">DRI website</a> for trouble-shooting information.
 240 </p>
 241
 242
 243 <h2>3.2 I'm seeing errors in depth (Z) buffering.  Why?</h2>
 244 <p>
 245 Make sure the ratio of the far to near clipping planes isn't too great.
 246 Look
 247 <a href="http://www.sgi.com/software/opengl/advanced97/notes/node18.html">
 248 here</a> for details.
 249 </p>
 250 <p>
 251 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 252 to clear than a 32-bit buffer but not as accurate.
 253 If you need a deeper you can modify the parameters to
 254 <code> glXChooseVisual</code> in your code.
 255 </p>
 256
 257
 258 <h2>3.3 Why Isn't depth buffering working at all?</h2>
 259 <p>
 260 Be sure you're requesting a depth buffered-visual.  If you set the MESA_DEBUG
 261 environment variable it will warn you about trying to enable depth testing
 262 when you don't have a depth buffer.
 263 </p>
 264 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 265 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 266 called with a non-zero value for GLX_DEPTH_SIZE.
 267 </p>
 268 <p>This discussion applies to stencil buffers, accumulation buffers and
 269 alpha channels too.
 270 </p>
 271
 272
 273 <h2>3.4 Why does glGetString() always return NULL?</h2>
 274 <p>
 275 Be sure you have an active/current OpenGL rendering context before
 276 calling glGetString.
 277 </p>
 278
 279
 280 <h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
 281 <p>
 282 If you're trying to draw a filled region by using GL_POINTS or GL_LINES
 283 and seeing holes or gaps it's because of a float-to-int rounding problem.
 284 But this is not a bug.
 285 See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
 286 Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
 287 will fix the problem.
 288 </p>
 289
 290 <br>
 291 <br>
 292
 293
 294 <a name="part4">
 295 </a><h1><a name="part4">4. Developer Questions</a></h1>
 296
 297 <h2><a name="part4">4.1 How can I contribute?</a></h2>
 298 <p>
 299 <a name="part4">First, join the Mesa3d-dev mailing list.  That's where Mesa development
 300 is discussed.
 301 </a></p>
 302 <p>
 303 <a name="part4">The </a><a href="http://www.opengl.org/developers/documentation/specs.html">
 304 OpenGL Specification</a> is the bible for OpenGL implemention work.
 305 You should read it.
 306 </p>
 307 <p>Most of the Mesa development work involves implementing new OpenGL
 308 extensions, writing hardware drivers (for the DRI), and code optimization.
 309 </p>
 310
 311 <h2>4.2 How do I write a new device driver?</h2>
 312 <p>
 313 Unfortunately, writing a device driver isn't easy.
 314 It requires detailed understanding of OpenGL, the Mesa code, and your
 315 target hardware/operating system.
 316 3D graphics are not simple.
 317 </p>
 318 <p>
 319 The best way to get started is to use an existing driver as your starting
 320 point.
 321 For a software driver, the X11 and OSMesa drivers are good examples.
 322 For a hardware driver, the Radeon and R200 DRI drivers are good examples.
 323 </p>
 324 <p>The DRI website has more information about writing hardware drivers.
 325 The process isn't well document because the Mesa driver interface changes
 326 over time, and we seldome have spare time for writing documentation.
 327 That being said, many people have managed to figure out the process.
 328 </p>
 329 <p>
 330 Joining the appropriate mailing lists and asking questions (and searching
 331 the archives) is a good way to get information.
 332 </p>
 333
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