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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, libGL.so, contains everything (the programming API,
 100     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 libGL.so library provides the GL and GLX API functions, a GLX
 107     protocol encoder, and a device driver loader.
 108 <li>The device driver modules (such as r200_dri.so) contain a built-in
 109     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://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://www.dsbox.com/minigl.html">miniGL</a>
 142 is a subset of OpenGL for PalmOS devices.
 143
 144 <p>
 145 <a href="http://bellard.org/TinyGL/">TinyGL</a>
 146 is a subset of OpenGL.
 147 </p>
 148
 149 <p>
 150 <a href="https://sourceforge.net/projects/softgl/">SoftGL</a>
 151 is an OpenGL subset for mobile devices.
 152 </p>
 153
 154 <p>
 155 <a href="http://chromium.sourceforge.net/">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">ClosedGL</a>
 163 is an OpenGL subset library for TI graphing calculators.
 164 </p>
 165
 166 <p>
 167 There may be other open OpenGL implementations, but Mesa is the most
 168 popular and feature-complete.
 169 </p>
 170
 171
 172 <h2 id="part2">2. Compilation and Installation Problems</h2>
 173
 174 <h3>2.1 What's the easiest way to install Mesa?</h3>
 175 <p>
 176 If you're using a Linux-based system, your distro CD most likely already
 177 has Mesa packages (like RPM or DEB) which you can easily install.
 178 </p>
 179
 180
 181 <h3>2.2 I get undefined symbols such as bgnpolygon, v3f, etc...</h3>
 182 <p>
 183 You're application is written in IRIS GL, not OpenGL.
 184 IRIS GL was the predecessor to OpenGL and is a different thing (almost)
 185 entirely.
 186 Mesa's not the solution.
 187 </p>
 188
 189
 190 <h3>2.3 Where is the GLUT library?</h3>
 191 <p>
 192 GLUT (OpenGL Utility Toolkit) is no longer in the separate MesaGLUT-x.y.z.tar.gz file.
 193 If you don't already have GLUT installed, you should grab
 194 <a href="http://freeglut.sourceforge.net/">freeglut</a>.
 195 </p>
 196
 197
 198 <h3>2.4 Where is the GLw library?</h3>
 199 <p>
 200 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.
 201 </p>
 202
 203
 204 <h2>2.5 What's the proper place for the libraries and headers?</h2>
 205 <p>
 206 On Linux-based systems you'll want to follow the
 207 <a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html">Linux ABI</a> standard.
 208 Basically you'll want the following:
 209 </p>
 210 <dl>
 211 <dt><code>/usr/include/GL/gl.h</code></dt>
 212 <dd>the main OpenGL header</dd>
 213 <dt><code>/usr/include/GL/glu.h</code></dt>
 214 <dd>the OpenGL GLU (utility) header</dd>
 215 <dt><code>/usr/include/GL/glx.h</code></dt>
 216 <dd>the OpenGL GLX header</dd>
 217 <dt><code>/usr/include/GL/glext.h</code></dt>
 218 <dd>the OpenGL extensions header</dd>
 219 <dt><code>/usr/include/GL/glxext.h</code></dt>
 220 <dd>the OpenGL GLX extensions header</dd>
 221 <dt><code>/usr/include/GL/osmesa.h</code></dt>
 222 <dd>the Mesa off-screen rendering header</dd>
 223 <dt><code>/usr/lib/libGL.so</code></dt>
 224 <dd>a symlink to <code>libGL.so.1</code></dd>
 225 <dt><code>/usr/lib/libGL.so.1</code></dt>
 226 <dd>a symlink to <code>libGL.so.1.xyz</code></dd>
 227 <dt><code>/usr/lib/libGL.so.xyz</code></dt>
 228 <dd>the actual OpenGL/Mesa library.  xyz denotes the
 229 Mesa version number.
 230 </dd>
 231 </dl>
 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
 251
 252 <h2 id="part3">3. Runtime / Rendering Problems</h2>
 253
 254 <h3>3.1 Rendering is slow / why isn't my graphics hardware being used?</h3>
 255 <p>
 256 If Mesa can't use its hardware accelerated drivers it falls back on one of its software renderers.
 257 (eg. classic swrast, softpipe or llvmpipe)
 258 </p>
 259 <p>
 260 You can run the <code>glxinfo</code> program to learn about your OpenGL
 261 library.
 262 Look for the <code>OpenGL vendor</code> and <code>OpenGL renderer</code> values.
 263 That will identify who's OpenGL library with which driver you're using and what sort of
 264 hardware it has detected.
 265 </p>
 266 <p>
 267 If you're using a hardware accelerated driver you want <code>direct rendering: Yes</code>.
 268 </p>
 269 <p>
 270 If your DRI-based driver isn't working, go to the
 271 <a href="https://dri.freedesktop.org/">DRI website</a> for trouble-shooting information.
 272 </p>
 273
 274
 275 <h3>3.2 I'm seeing errors in depth (Z) buffering.  Why?</h3>
 276 <p>
 277 Make sure the ratio of the far to near clipping planes isn't too great.
 278 Look
 279 <a href="https://www.opengl.org/resources/faq/technical/depthbuffer.htm#0040">here</a>
 280 for details.
 281 </p>
 282 <p>
 283 Mesa uses a 16-bit depth buffer by default which is smaller and faster
 284 to clear than a 32-bit buffer but not as accurate.
 285 If you need a deeper you can modify the parameters to
 286 <code>glXChooseVisual</code> in your code.
 287 </p>
 288
 289
 290 <h3>3.3 Why Isn't depth buffering working at all?</h3>
 291 <p>
 292 Be sure you're requesting a depth buffered-visual.  If you set the
 293 <code>MESA_DEBUG</code> environment variable it will warn you about trying
 294 to enable depth testing when you don't have a depth buffer.
 295 </p>
 296 <p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
 297 with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
 298 called with a non-zero value for <code>GLX_DEPTH_SIZE</code>.
 299 </p>
 300 <p>This discussion applies to stencil buffers, accumulation buffers and
 301 alpha channels too.
 302 </p>
 303
 304
 305 <h3>3.4 Why does <code>glGetString()</code> always return <code>NULL</code>?</h3>
 306 <p>
 307 Be sure you have an active/current OpenGL rendering context before
 308 calling <code>glGetString</code>.
 309 </p>
 310
 311
 312 <h3>3.5 <code>GL_POINTS</code> and <code>GL_LINES</code> don't touch the
 313 right pixels</h3>
 314 <p>
 315 If you're trying to draw a filled region by using <code>GL_POINTS</code> or
 316 <code>GL_LINES</code> and seeing holes or gaps it's because of a float-to-int
 317 rounding problem. But this is not a bug. See Appendix H of the OpenGL
 318 Programming Guide - "OpenGL Correctness Tips". Basically, applying a
 319 translation of (0.375, 0.375, 0.0) to your coordinates will fix the problem.
 320 </p>
 321
 322
 323 <h2 id="part4">4. Developer Questions</h2>
 324
 325 <h3>4.1 How can I contribute?</h3>
 326 <p>
 327 First, join the <a href="lists.html">mesa-dev mailing list</a>.
 328 That's where Mesa development is discussed.
 329 </p>
 330 <p>
 331 The <a href="https://www.opengl.org/documentation">
 332 OpenGL Specification</a> is the bible for OpenGL implementation work.
 333 You should read it.
 334 </p>
 335 <p>Most of the Mesa development work involves implementing new OpenGL
 336 extensions, writing hardware drivers (for the DRI), and code optimization.
 337 </p>
 338
 339 <h3>4.2 How do I write a new device driver?</h3>
 340 <p>
 341 Unfortunately, writing a device driver isn't easy.
 342 It requires detailed understanding of OpenGL, the Mesa code, and your
 343 target hardware/operating system.
 344 3D graphics are not simple.
 345 </p>
 346 <p>
 347 The best way to get started is to use an existing driver as your starting
 348 point.
 349 For a classic hardware driver, the i965 driver is a good example.
 350 For a Gallium3D hardware driver, the r300g, r600g and the i915g are good examples.
 351 </p>
 352 <p>The DRI website has more information about writing hardware drivers.
 353 The process isn't well document because the Mesa driver interface changes
 354 over time, and we seldom have spare time for writing documentation.
 355 That being said, many people have managed to figure out the process.
 356 </p>
 357 <p>
 358 Joining the appropriate mailing lists and asking questions (and searching
 359 the archives) is a good way to get information.
 360 </p>
 361
 362
 363 <h3>4.3 Why isn't <code>GL_EXT_texture_compression_s3tc</code> implemented in
 364 Mesa?</h3>
 365 <p>
 366 Oh but it is! Prior to 2nd October 2017, the Mesa project did not include s3tc
 367 support due to intellectual property (IP) and/or patent issues around the s3tc
 368 algorithm.
 369 </p>
 370 <p>
 371 As of Mesa 17.3.0, Mesa now officially supports s3tc, as the patent has expired.
 372 </p>
 373 <p>
 374 In versions prior to this, a 3rd party <a href="https://dri.freedesktop.org/wiki/S3TC">
 375 plug-in library</a> was required.
 376 </p>
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