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  11   The Mesa 3D Graphics Library
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  16
  17 <h1>Frequently Asked Questions</h1>
  18 Last updated: 19 September 2018
  19
  20 <br>
  21 <br>
  22 <h2>Index</h2>
  23 <ol>
  24   <li><a href="#part1">High-level Questions and Answers</a></li>
  25   <li><a href="#part2">Compilation and Installation Problems</a></li>
  26   <li><a href="#part3">Runtime / Rendering Problems</a></li>
  27   <li><a href="#part4">Developer Questions</a></li>
  28 </ol>
  29 <br>
  30 <br>
  31
  32 <h2 id="part1">1. High-level Questions and Answers</h2>
  33
  34 <h3>1.1 What is Mesa?</h3>
  35 <p>
  36 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 href="https://www.opengl.org/">OpenGL website</a> for more
  39 information.
  40 </p>
  41 <p>
  42 Mesa 9.x supports the OpenGL 3.1 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 X.org.
  50 </p>
  51 <ul>
  52   <li>See the <a href="https://dri.freedesktop.org/">DRI website</a>
  53   for more information.</li>
  54   <li>See <a href="https://01.org/linuxgraphics">01.org</a>
  55   for more information about Intel drivers.</li>
  56   <li>See <a href="https://nouveau.freedesktop.org">nouveau.freedesktop.org</a>
  57   for more information about Nouveau drivers.</li>
  58   <li>See <a href="https://www.x.org/wiki/RadeonFeature">www.x.org/wiki/RadeonFeature</a>
  59   for more information about Radeon drivers.</li>
  60 </ul>
  61
  62 <h2>1.3 What purpose does Mesa serve today?</h2>
  63 <p>
  64 Hardware-accelerated OpenGL implementations are available for most popular
  65 operating systems today.
  66 Still, Mesa serves at least these purposes:
  67 </p>
  68 <ul>
  69 <li>Mesa is used as the core of the open-source X.org DRI
  70     hardware drivers.
  71 </li>
  72 <li>Mesa is quite portable and allows OpenGL to be used on systems
  73     that have no other OpenGL solution.
  74 </li>
  75 <li>Software rendering with Mesa serves as a reference for validating the
  76     hardware drivers.
  77 </li>
  78 <li>A software implementation of OpenGL is useful for experimentation,
  79     such as testing new rendering techniques.
  80 </li>
  81 <li>Mesa can render images with deep color channels: 16-bit integer
  82     and 32-bit floating point color channels are supported.
  83     This capability is only now appearing in hardware.
  84 </li>
  85 <li>Mesa's internal limits (max lights, clip planes, texture size, etc) can be
  86     changed for special needs (hardware limits are hard to overcome).
  87 </li>
  88 </ul>
  89
  90
  91 <h2>1.4 What's the difference between "Stand-Alone" Mesa and the DRI drivers?</h2>
  92 <p>
  93 <em>Stand-alone Mesa</em> is the original incarnation of Mesa.
  94 On systems running the X Window System it does all its rendering through
  95 the Xlib API:
  96 </p>
  97 <ul>
  98 <li>The GLX API is supported, but it's really just an emulation of the
  99      real thing.
 100 <li>The GLX wire protocol is not supported and there's no OpenGL extension
 101     loaded by the X server.
 102 <li>There is no hardware acceleration.
 103 <li>The OpenGL library, libGL.so, contains everything (the programming API,
 104     the GLX functions and all the rendering code).
 105 </ul>
 106 <p>
 107 Alternately, Mesa acts as the core for a number of OpenGL hardware drivers
 108 within the DRI (Direct Rendering Infrastructure):
 109 <ul>
 110 <li>The libGL.so library provides the GL and GLX API functions, a GLX
 111     protocol encoder, and a device driver loader.
 112 <li>The device driver modules (such as r200_dri.so) contain a built-in
 113     copy of the core Mesa code.
 114 <li>The X server loads the GLX module.
 115     The GLX module decodes incoming GLX protocol and dispatches the commands
 116     to a rendering module.
 117     For the DRI, this module is basically a software Mesa renderer.
 118 </ul>
 119
 120
 121
 122 <h2>1.5 How do I upgrade my DRI installation to use a new Mesa release?</h2>
 123 <p>
 124 This wasn't easy in the past.
 125 Now, the DRI drivers are included in the Mesa tree and can be compiled
 126 separately from the X server.
 127 Just follow the Mesa <a href="install.html">compilation instructions</a>.
 128 </p>
 129
 130
 131 <h2>1.6 Are there other open-source implementations of OpenGL?</h2>
 132 <p>
 133 Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html">
 134 OpenGL Sample Implementation (SI)</a> is available.
 135 The SI was written during the time that OpenGL was originally designed.
 136 Unfortunately, development of the SI has stagnated.
 137 Mesa is much more up to date with modern features and extensions.
 138 </p>
 139
 140 <p>
 141 <a href="https://sourceforge.net/projects/ogl-es/">Vincent</a> is
 142 an open-source implementation of OpenGL ES for mobile devices.
 143
 144 <p>
 145 <a href="http://www.dsbox.com/minigl.html">miniGL</a>
 146 is a subset of OpenGL for PalmOS devices.
 147
 148 <p>
 149 <a href="http://bellard.org/TinyGL/">TinyGL</a>
 150 is a subset of OpenGL.
 151 </p>
 152
 153 <p>
 154 <a href="https://sourceforge.net/projects/softgl/">SoftGL</a>
 155 is an OpenGL subset for mobile devices.
 156 </p>
 157
 158 <p>
 159 <a href="http://chromium.sourceforge.net/">Chromium</a>
 160 isn't a conventional OpenGL implementation (it's layered upon OpenGL),
 161 but it does export the OpenGL API.  It allows tiled rendering, sort-last
 162 rendering, etc.
 163 </p>
 164
 165 <p>
 166 <a href="http://www.ticalc.org/archives/files/fileinfo/361/36173.html">ClosedGL</a>
 167 is an OpenGL subset library for TI graphing calculators.
 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 <h2 id="part2">2. Compilation and Installation Problems</h2>
 182
 183
 184 <h3>2.1 What's the easiest way to install Mesa?</h3>
 185 <p>
 186 If you're using a Linux-based system, your distro CD most likely already
 187 has Mesa packages (like RPM or DEB) which you can easily install.
 188 </p>
 189
 190
 191 <h3>2.2 I get undefined symbols such as bgnpolygon, v3f, etc...</h3>
 192 <p>
 193 You're application is written in IRIS GL, not OpenGL.
 194 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 195 entirely.
 196 Mesa's not the solution.
 197 </p>
 198
 199
 200 <h3>2.3 Where is the GLUT library?</h3>
 201 <p>
 202 GLUT (OpenGL Utility Toolkit) is no longer in the separate MesaGLUT-x.y.z.tar.gz file.
 203 If you don't already have GLUT installed, you should grab
 204 <a href="http://freeglut.sourceforge.net/">freeglut</a>.
 205 </p>
 206
 207
 208 <h3>2.4 Where is the GLw library?</h3>
 209 <p>
 210 GLw (OpenGL widget library) is now available from a separate <a href="https://cgit.freedesktop.org/mesa/glw/">git repository</a>.  Unless you're using very old Xt/Motif applications with OpenGL, you shouldn't need it.
 211 </p>
 212
 213
 214 <h2>2.5 What's the proper place for the libraries and headers?</h2>
 215 <p>
 216 On Linux-based systems you'll want to follow the
 217 <a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html">Linux ABI</a> standard.
 218 Basically you'll want the following:
 219 </p>
 220 <ul>
 221 <li>/usr/include/GL/gl.h - the main OpenGL header
 222 </li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
 223 </li><li>/usr/include/GL/glx.h - the OpenGL GLX header
 224 </li><li>/usr/include/GL/glext.h - the OpenGL extensions header
 225 </li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
 226 </li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
 227 </li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
 228 </li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
 229 </li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library.  xyz denotes the
 230 Mesa version number.
 231 </li></ul>
 232 <p>
 233 When configuring Mesa, there are three meson options that affect the install
 234 location that you should take care with: <code>--prefix</code>,
 235 <code>--libdir</code>, and <code>-D dri-drivers-path</code>. To install Mesa
 236 into the system location where it will be available for all programs to use, set
 237 <code>--prefix=/usr</code>. Set <code>--libdir</code> to where your Linux
 238 distribution installs system libraries, usually either <code>/usr/lib</code> or
 239 <code>/usr/lib64</code>. Set <code>-D dri-drivers-path</code> to the directory
 240 where your Linux distribution installs DRI drivers. To find your system's DRI
 241 driver directory, try executing <code>find /usr -type d -name dri</code>. For
 242 example, if the <code>find</code> command listed <code>/usr/lib64/dri</code>,
 243 then set <code>-D dri-drivers-path=/usr/lib64/dri</code>.
 244 </p>
 245 <p>
 246 After determining the correct values for the install location, configure Mesa
 247 with <code>meson configure --prefix=/usr --libdir=xxx -D dri-drivers-path=xxx</code>
 248 and then install with <code>sudo ninja install</code>.
 249 </p>
 250 <br>
 251 <br>
 252
 253
 254 <h2 id="part3">3. Runtime / Rendering Problems</h2>
 255
 256 <h3>3.1 Rendering is slow / why isn't my graphics hardware being used?</h3>
 257 <p>
 258 If Mesa can't use its hardware accelerated drivers it falls back on one of its software renderers.
 259 (eg. classic swrast, softpipe or llvmpipe)
 260 </p>
 261 <p>
 262 You can run the <code>glxinfo</code> program to learn about your OpenGL
 263 library.
 264 Look for the <code>OpenGL vendor</code> and <code>OpenGL renderer</code> values.
 265 That will identify who's OpenGL library with which driver you're using and what sort of
 266 hardware it has detected.
 267 </p>
 268 <p>
 269 If you're using a hardware accelerated driver you want <code>direct rendering: Yes</code>.
 270 </p>
 271 <p>
 272 If your DRI-based driver isn't working, go to the
 273 <a href="https://dri.freedesktop.org/">DRI website</a> for trouble-shooting information.
 274 </p>
 275
 276
 277 <h3>3.2 I'm seeing errors in depth (Z) buffering.  Why?</h3>
 278 <p>
 279 Make sure the ratio of the far to near clipping planes isn't too great.
 280 Look
 281 <a href="https://www.opengl.org/resources/faq/technical/depthbuffer.htm#0040">here</a>
 282 for details.
 283 </p>
 284 <p>
 285 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 286 to clear than a 32-bit buffer but not as accurate.
 287 If you need a deeper you can modify the parameters to
 288 <code> glXChooseVisual</code> in your code.
 289 </p>
 290
 291
 292 <h3>3.3 Why Isn't depth buffering working at all?</h3>
 293 <p>
 294 Be sure you're requesting a depth buffered-visual.  If you set the MESA_DEBUG
 295 environment variable it will warn you about trying to enable depth testing
 296 when you don't have a depth buffer.
 297 </p>
 298 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 299 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 300 called with a non-zero value for GLX_DEPTH_SIZE.
 301 </p>
 302 <p>This discussion applies to stencil buffers, accumulation buffers and
 303 alpha channels too.
 304 </p>
 305
 306
 307 <h3>3.4 Why does glGetString() always return NULL?</h3>
 308 <p>
 309 Be sure you have an active/current OpenGL rendering context before
 310 calling glGetString.
 311 </p>
 312
 313
 314 <h3>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h3>
 315 <p>
 316 If you're trying to draw a filled region by using GL_POINTS or GL_LINES
 317 and seeing holes or gaps it's because of a float-to-int rounding problem.
 318 But this is not a bug.
 319 See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
 320 Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
 321 will fix the problem.
 322 </p>
 323
 324 <br>
 325 <br>
 326
 327
 328 <h2 id="part4">4. Developer Questions</h2>
 329
 330 <h3>4.1 How can I contribute?</h3>
 331 <p>
 332 First, join the <a href="lists.html">mesa-dev mailing list</a>.
 333 That's where Mesa development is discussed.
 334 </p>
 335 <p>
 336 The <a href="https://www.opengl.org/documentation">
 337 OpenGL Specification</a> is the bible for OpenGL implementation work.
 338 You should read it.
 339 </p>
 340 <p>Most of the Mesa development work involves implementing new OpenGL
 341 extensions, writing hardware drivers (for the DRI), and code optimization.
 342 </p>
 343
 344 <h3>4.2 How do I write a new device driver?</h3>
 345 <p>
 346 Unfortunately, writing a device driver isn't easy.
 347 It requires detailed understanding of OpenGL, the Mesa code, and your
 348 target hardware/operating system.
 349 3D graphics are not simple.
 350 </p>
 351 <p>
 352 The best way to get started is to use an existing driver as your starting
 353 point.
 354 For a classic hardware driver, the i965 driver is a good example.
 355 For a Gallium3D hardware driver, the r300g, r600g and the i915g are good examples.
 356 </p>
 357 <p>The DRI website has more information about writing hardware drivers.
 358 The process isn't well document because the Mesa driver interface changes
 359 over time, and we seldom have spare time for writing documentation.
 360 That being said, many people have managed to figure out the process.
 361 </p>
 362 <p>
 363 Joining the appropriate mailing lists and asking questions (and searching
 364 the archives) is a good way to get information.
 365 </p>
 366
 367
 368 <h3>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa?</h3>
 369 <p>
 370 Oh but it is! Prior to 2nd October 2017, the Mesa project did not include s3tc
 371 support due to intellectual property (IP) and/or patent issues around the s3tc
 372 algorithm.
 373 </p>
 374 <p>
 375 As of Mesa 17.3.0, Mesa now officially supports s3tc, as the patent has expired.
 376 </p>
 377 <p>
 378 In versions prior to this, a 3rd party <a href="https://dri.freedesktop.org/wiki/S3TC">
 379 plug-in library</a> was required.
 380 </p>
 381
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