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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 <h2>Index</h2>
  21 <ol>
  22   <li><a href="#part1">High-level Questions and Answers</a></li>
  23   <li><a href="#part2">Compilation and Installation Problems</a></li>
  24   <li><a href="#part3">Runtime / Rendering Problems</a></li>
  25   <li><a href="#part4">Developer Questions</a></li>
  26 </ol>
  27
  28 <h2 id="part1">1. High-level Questions and Answers</h2>
  29
  30 <h3>1.1 What is Mesa?</h3>
  31 <p>
  32 Mesa is an open-source implementation of the OpenGL specification.
  33 OpenGL is a programming library for writing interactive 3D applications.
  34 See the <a href="https://www.opengl.org/">OpenGL website</a> for more
  35 information.
  36 </p>
  37 <p>
  38 Mesa 9.x supports the OpenGL 3.1 specification.
  39 </p>
  40
  41
  42 <h2>1.2 Does Mesa support/use graphics hardware?</h2>
  43 <p>
  44 Yes.  Specifically, Mesa serves as the OpenGL core for the open-source DRI
  45 drivers for X.org.
  46 </p>
  47 <ul>
  48   <li>See the <a href="https://dri.freedesktop.org/">DRI website</a>
  49   for more information.</li>
  50   <li>See <a href="https://01.org/linuxgraphics">01.org</a>
  51   for more information about Intel drivers.</li>
  52   <li>See <a href="https://nouveau.freedesktop.org">nouveau.freedesktop.org</a>
  53   for more information about Nouveau drivers.</li>
  54   <li>See <a href="https://www.x.org/wiki/RadeonFeature">www.x.org/wiki/RadeonFeature</a>
  55   for more information about Radeon drivers.</li>
  56 </ul>
  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 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 </p>
  93 <ul>
  94 <li>The GLX API is supported, but it's really just an emulation of the
  95      real thing.
  96 <li>The GLX wire protocol is not supported and there's no OpenGL extension
  97     loaded by the X server.
  98 <li>There is no hardware acceleration.
  99 <li>The OpenGL library, <code>libGL.so</code>, contains everything (the
 100     programming API, the GLX functions and all the rendering code).
 101 </ul>
 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 <code>libGL.so</code> library provides the GL and GLX API functions,
 107     a GLX protocol encoder, and a device driver loader.
 108 <li>The device driver modules (such as <code>r200_dri.so</code>) contain
 109     a built-in 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://web.archive.org/web/20171010115110_/http://oss.sgi.com/projects/ogl-sample/index.html">
 130 OpenGL Sample Implementation (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="https://sourceforge.net/projects/ogl-es/">Vincent</a> is
 138 an open-source implementation of OpenGL ES for mobile devices.
 139
 140 <p>
 141 <a href="http://web.archive.org/web/20130830162848/http://www.dsbox.com/minigl.html">miniGL</a>
 142 is a subset of OpenGL for PalmOS devices. The website is gone, but the source
 143 code can still be found on <a href="https://sourceforge.net/projects/minigl/">sourceforge.net</a>.
 144
 145 <p>
 146 <a href="http://bellard.org/TinyGL/">TinyGL</a>
 147 is a subset of OpenGL.
 148 </p>
 149
 150 <p>
 151 <a href="https://sourceforge.net/projects/softgl/">SoftGL</a>
 152 is an OpenGL subset for mobile devices.
 153 </p>
 154
 155 <p>
 156 <a href="http://chromium.sourceforge.net/">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">ClosedGL</a>
 164 is an OpenGL subset library for TI 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 <h2 id="part2">2. Compilation and Installation Problems</h2>
 174
 175 <h3>2.1 What's the easiest way to install Mesa?</h3>
 176 <p>
 177 If you're using a Linux-based system, your distro CD most likely already
 178 has Mesa packages (like RPM or DEB) which you can easily install.
 179 </p>
 180
 181
 182 <h3>2.2 I get undefined symbols such as bgnpolygon, v3f, etc...</h3>
 183 <p>
 184 You're application is written in IRIS GL, not OpenGL.
 185 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 186 entirely.
 187 Mesa's not the solution.
 188 </p>
 189
 190
 191 <h3>2.3 Where is the GLUT library?</h3>
 192 <p>
 193 GLUT (OpenGL Utility Toolkit) is no longer in the separate
 194 <code>MesaGLUT-x.y.z.tar.gz</code> file.
 195 If you don't already have GLUT installed, you should grab
 196 <a href="http://freeglut.sourceforge.net/">freeglut</a>.
 197 </p>
 198
 199
 200 <h3>2.4 Where is the GLw library?</h3>
 201 <p>
 202 GLw (OpenGL widget library) is now available from a separate <a href="https://gitlab.freedesktop.org/mesa/glw">git repository</a>.  Unless you're using very old Xt/Motif applications with OpenGL, you shouldn't need it.
 203 </p>
 204
 205
 206 <h2>2.5 What's the proper place for the libraries and headers?</h2>
 207 <p>
 208 On Linux-based systems you'll want to follow the
 209 <a href="https://www.khronos.org/registry/OpenGL/ABI/">Linux ABI</a> standard.
 210 Basically you'll want the following:
 211 </p>
 212 <dl>
 213 <dt><code>/usr/include/GL/gl.h</code></dt>
 214 <dd>the main OpenGL header</dd>
 215 <dt><code>/usr/include/GL/glu.h</code></dt>
 216 <dd>the OpenGL GLU (utility) header</dd>
 217 <dt><code>/usr/include/GL/glx.h</code></dt>
 218 <dd>the OpenGL GLX header</dd>
 219 <dt><code>/usr/include/GL/glext.h</code></dt>
 220 <dd>the OpenGL extensions header</dd>
 221 <dt><code>/usr/include/GL/glxext.h</code></dt>
 222 <dd>the OpenGL GLX extensions header</dd>
 223 <dt><code>/usr/include/GL/osmesa.h</code></dt>
 224 <dd>the Mesa off-screen rendering header</dd>
 225 <dt><code>/usr/lib/libGL.so</code></dt>
 226 <dd>a symlink to <code>libGL.so.1</code></dd>
 227 <dt><code>/usr/lib/libGL.so.1</code></dt>
 228 <dd>a symlink to <code>libGL.so.1.xyz</code></dd>
 229 <dt><code>/usr/lib/libGL.so.xyz</code></dt>
 230 <dd>the actual OpenGL/Mesa library.  xyz denotes the
 231 Mesa version number.
 232 </dd>
 233 </dl>
 234 <p>
 235 When configuring Mesa, there are three meson options that affect the install
 236 location that you should take care with: <code>--prefix</code>,
 237 <code>--libdir</code>, and <code>-D dri-drivers-path</code>. To install Mesa
 238 into the system location where it will be available for all programs to use, set
 239 <code>--prefix=/usr</code>. Set <code>--libdir</code> to where your Linux
 240 distribution installs system libraries, usually either <code>/usr/lib</code> or
 241 <code>/usr/lib64</code>. Set <code>-D dri-drivers-path</code> to the directory
 242 where your Linux distribution installs DRI drivers. To find your system's DRI
 243 driver directory, try executing <code>find /usr -type d -name dri</code>. For
 244 example, if the <code>find</code> command listed <code>/usr/lib64/dri</code>,
 245 then set <code>-D dri-drivers-path=/usr/lib64/dri</code>.
 246 </p>
 247 <p>
 248 After determining the correct values for the install location, configure Mesa
 249 with <code>meson configure --prefix=/usr --libdir=xxx -D dri-drivers-path=xxx</code>
 250 and then install with <code>sudo ninja install</code>.
 251 </p>
 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/archives/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
 295 <code>MESA_DEBUG</code> environment variable it will warn you about trying
 296 to enable depth testing 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 <code>GLX_DEPTH_SIZE</code>.
 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 <code>glGetString()</code> always return <code>NULL</code>?</h3>
 308 <p>
 309 Be sure you have an active/current OpenGL rendering context before
 310 calling <code>glGetString</code>.
 311 </p>
 312
 313
 314 <h3>3.5 <code>GL_POINTS</code> and <code>GL_LINES</code> don't touch the
 315 right pixels</h3>
 316 <p>
 317 If you're trying to draw a filled region by using <code>GL_POINTS</code> or
 318 <code>GL_LINES</code> and seeing holes or gaps it's because of a float-to-int
 319 rounding problem. But this is not a bug. See Appendix H of the OpenGL
 320 Programming Guide - "OpenGL Correctness Tips". Basically, applying a
 321 translation of (0.375, 0.375, 0.0) to your coordinates will fix the problem.
 322 </p>
 323
 324
 325 <h2 id="part4">4. Developer Questions</h2>
 326
 327 <h3>4.1 How can I contribute?</h3>
 328 <p>
 329 First, join the <a href="lists.html">mesa-dev mailing list</a>.
 330 That's where Mesa development is discussed.
 331 </p>
 332 <p>
 333 The <a href="https://www.opengl.org/documentation">
 334 OpenGL Specification</a> is the bible for OpenGL implementation work.
 335 You should read it.
 336 </p>
 337 <p>Most of the Mesa development work involves implementing new OpenGL
 338 extensions, writing hardware drivers (for the DRI), and code optimization.
 339 </p>
 340
 341 <h3>4.2 How do I write a new device driver?</h3>
 342 <p>
 343 Unfortunately, writing a device driver isn't easy.
 344 It requires detailed understanding of OpenGL, the Mesa code, and your
 345 target hardware/operating system.
 346 3D graphics are not simple.
 347 </p>
 348 <p>
 349 The best way to get started is to use an existing driver as your starting
 350 point.
 351 For a classic hardware driver, the i965 driver is a good example.
 352 For a Gallium3D hardware driver, the r300g, r600g and the i915g are good examples.
 353 </p>
 354 <p>The DRI website has more information about writing hardware drivers.
 355 The process isn't well document because the Mesa driver interface changes
 356 over time, and we seldom have spare time for writing documentation.
 357 That being said, many people have managed to figure out the process.
 358 </p>
 359 <p>
 360 Joining the appropriate mailing lists and asking questions (and searching
 361 the archives) is a good way to get information.
 362 </p>
 363
 364
 365 <h3>4.3 Why isn't <code>GL_EXT_texture_compression_s3tc</code> implemented in
 366 Mesa?</h3>
 367 <p>
 368 Oh but it is! Prior to 2nd October 2017, the Mesa project did not include s3tc
 369 support due to intellectual property (IP) and/or patent issues around the s3tc
 370 algorithm.
 371 </p>
 372 <p>
 373 As of Mesa 17.3.0, Mesa now officially supports s3tc, as the patent has expired.
 374 </p>
 375 <p>
 376 In versions prior to this, a 3rd party <a href="https://dri.freedesktop.org/wiki/S3TC">
 377 plug-in library</a> was required.
 378 </p>
 379
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