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   9 <h1>Mesa Frequently Asked Questions</h1>
  10 Last updated: 6 August 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 <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 OpenGL Sample Implemenation (SI)</a> is available.
 107 The SI was written during the time that OpenGL was originally designed.
 108 Unfortunately, development of the SI has stagnated.
 109 Mesa is much more up to date with modern features and extensions.
 110 </p>
 111 <p>
 112 <a href="http://www.dsbox.com/minigl.html">miniGL</a> is a subset of OpenGL
 113 for PalmOS devices.
 114
 115 <a href="http://fabrice.bellard.free.fr/TinyGL/">TinyGL</a> is another
 116 subset of OpenGL.
 117 </p>
 118 <p>
 119 There may be others but Mesa is the most popular and feature-complete.
 120 </p>
 121
 122 <br>
 123 <br>
 124
 125
 126 <a name="part2">
 127 </a><h1><a name="part2">2. Compilation and Installation Problems</a></h1>
 128
 129
 130 <h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2>
 131 <p>
 132 <a name="part2">If you're using a Linux-based system, your distro CD most likely already
 133 has Mesa packages (like RPM or DEB) which you can easily install.
 134 </a></p>
 135
 136
 137 <h2><a name="part2">2.2 Running <code>configure; make</code> Doesn't Work</a></h2>
 138 <p>
 139 <a name="part2">Unfortunately, the GNU autoconf/automake/libtool system doesn't seem to work
 140 too well on non GNU/Linux systems, even after installing gmake, gcc, etc.
 141 For that reason, Mesa's <b>old-style</b> makefile system is still included.
 142 The old-style system uses good old traditional Makefiles.  Try the following:
 143 </a></p><pre><a name="part2">  cd Mesa-x.y.z
 144   cp Makefile.X11 Makefile
 145   make
 146 </a></pre>
 147 <a name="part2">You'll see a list of system configurations from which to choose.
 148 For example:
 149 </a><pre><a name="part2">  make linux-x86
 150 </a></pre>
 151 <p>
 152 <a name="part2">If you're experienced with GNU autoconf/automake/libtool and think you can help
 153 with maintence, contact the Mesa developers.
 154 FYI, the Mesa developers generally don't use the autoconf/automake system.
 155 We're especially annoyed with the fact that a +5000-line script (libtool)
 156 is needed to make shared libraries (ugh).
 157 </a></p>
 158
 159 <h2><a name="part2">2.3 Mesa still doesn't compile</a></h2>
 160 <p>
 161 <a name="part2">If the old-style Makefile system doesn't work either, make sure you have
 162 the most recent version of Mesa.
 163 Otherwise, file a bug report or post to the Mesa3d-users mailing list.
 164 Give as much info as possible when describing your problem.
 165 </a></p>
 166
 167
 168 <h2><a name="part2">2.4 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2>
 169 <p>
 170 <a name="part2">You're application is written in IRIS GL, not OpenGL.
 171 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 172 entirely.
 173 Mesa's not the solution.
 174 </a></p>
 175
 176
 177 <h2><a name="part2">2.5 Where is the GLUT library?</a></h2>
 178 <p>
 179 <a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaDemos-x.y.z.tar.gz file.
 180 If you don't already have GLUT installed, you should grab the MesaDemos
 181 package and unpack it before compiling Mesa.
 182 </a></p>
 183
 184
 185
 186 <h2><a name="part2">2.6 What's the proper place for the libraries and headers?</a></h2>
 187 <p>
 188 <a name="part2">On Linux-based systems you'll want to follow the
 189 </a><a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html">Linux ABI</a>
 190 standard.
 191 Basically you'll want the following:
 192 </p>
 193 <ul>
 194 <li>/usr/include/GL/gl.h - the main OpenGL header
 195 </li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
 196 </li><li>/usr/include/GL/glx.h - the OpenGL GLX header
 197 </li><li>/usr/include/GL/glext.h - the OpenGL extensions header
 198 </li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
 199 </li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
 200 </li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
 201 </li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
 202 </li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library.  xyz denotes the
 203 Mesa version number.
 204 </li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1
 205 </li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz
 206 </li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library.  xyz denotes the Mesa
 207 version number.
 208 </li></ul>
 209 <p>
 210 After installing XFree86 and the DRI drivers, some of these files
 211 may be symlinks into the /usr/X11R6/ tree.
 212 </p>
 213 <p>
 214 The old-style Makefile system doesn't install the Mesa libraries; it's
 215 up to you to copy them (and the headers) to the right place.
 216 </p>
 217 <p>
 218 The GLUT header and library should go in the same directories.
 219 </p>
 220 <br>
 221 <br>
 222
 223
 224 <a name="part3">
 225 </a><h1><a name="part3">3. Runtime / Rendering Problems</a></h1>
 226
 227 <h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2>
 228 <p>
 229 <a name="part3">Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any
 230 support for hardware acceleration (with the exception of the 3DFX Voodoo
 231 driver).
 232 </a></p>
 233 <p>
 234 <a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
 235 for your particular hardware.
 236 </a></p>
 237 <p>
 238 <a name="part3">You can run the <code>glxinfo</code> program to learn about your OpenGL
 239 library.
 240 Look for the GL_VENDOR and GL_RENDERER values.
 241 That will identify who's OpenGL library you're using and what sort of
 242 hardware it has detected.
 243 </a></p>
 244 <p>
 245 <a name="part3">If your DRI-based driver isn't working, go to the
 246 </a><a href="http://dri.sf.net/">DRI website</a> for trouble-shooting information.
 247 </p>
 248
 249
 250 <h2>3.2 I'm seeing errors in depth (Z) buffering.  Why?</h2>
 251 <p>
 252 Make sure the ratio of the far to near clipping planes isn't too great.
 253 Look
 254 <a href="http://www.sgi.com/software/opengl/advanced97/notes/node18.html">
 255 here</a> for details.
 256 </p>
 257 <p>
 258 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 259 to clear than a 32-bit buffer but not as accurate.
 260 If you need a deeper you can modify the parameters to
 261 <code> glXChooseVisual</code> in your code.
 262 </p>
 263
 264
 265 <h2>3.3 Why Isn't depth buffering working at all?</h2>
 266 <p>
 267 Be sure you're requesting a depth buffered-visual.  If you set the MESA_DEBUG
 268 environment variable it will warn you about trying to enable depth testing
 269 when you don't have a depth buffer.
 270 </p>
 271 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 272 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 273 called with a non-zero value for GLX_DEPTH_SIZE.
 274 </p>
 275 <p>This discussion applies to stencil buffers, accumulation buffers and
 276 alpha channels too.
 277 </p>
 278
 279
 280 <h2>3.4 Why does glGetString() always return NULL?</h2>
 281 <p>
 282 Be sure you have an active/current OpenGL rendering context before
 283 calling glGetString.
 284 </p>
 285
 286
 287 <h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
 288 <p>
 289 If you're trying to draw a filled region by using GL_POINTS or GL_LINES
 290 and seeing holes or gaps it's because of a float-to-int rounding problem.
 291 But this is not a bug.
 292 See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
 293 Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
 294 will fix the problem.
 295 </p>
 296
 297 <br>
 298 <br>
 299
 300
 301 <a name="part4">
 302 </a><h1><a name="part4">4. Developer Questions</a></h1>
 303
 304 <h2><a name="part4">4.1 How can I contribute?</a></h2>
 305 <p>
 306 <a name="part4">First, join the Mesa3d-dev mailing list.  That's where Mesa development
 307 is discussed.
 308 </a></p>
 309 <p>
 310 <a name="part4">The </a><a href="http://www.opengl.org/developers/documentation/specs.html">
 311 OpenGL Specification</a> is the bible for OpenGL implemention work.
 312 You should read it.
 313 </p>
 314 <p>Most of the Mesa development work involves implementing new OpenGL
 315 extensions, writing hardware drivers (for the DRI), and code optimization.
 316 </p>
 317
 318 <h2>4.2 How do I write a new device driver?</h2>
 319 <p>
 320 Unfortunately, writing a device driver isn't easy.
 321 It requires detailed understanding of OpenGL, the Mesa code, and your
 322 target hardware/operating system.
 323 3D graphics are not simple.
 324 </p>
 325 <p>
 326 The best way to get started is to use an existing driver as your starting
 327 point.
 328 For a software driver, the X11 and OSMesa drivers are good examples.
 329 For a hardware driver, the Radeon and R200 DRI drivers are good examples.
 330 </p>
 331 <p>The DRI website has more information about writing hardware drivers.
 332 The process isn't well document because the Mesa driver interface changes
 333 over time, and we seldome have spare time for writing documentation.
 334 That being said, many people have managed to figure out the process.
 335 </p>
 336 <p>
 337 Joining the appropriate mailing lists and asking questions (and searching
 338 the archives) is a good way to get information.
 339 </p>
 340
 341
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