| Frequently Asked Questions |
| ========================== |
| |
| Last updated: 19 September 2018 |
| |
| 1. High-level Questions and Answers |
| ----------------------------------- |
| |
| 1.1 What is Mesa? |
| ~~~~~~~~~~~~~~~~~ |
| |
| Mesa is an open-source implementation of the OpenGL specification. |
| OpenGL is a programming library for writing interactive 3D applications. |
| See the `OpenGL website <https://www.opengl.org/>`__ for more |
| information. |
| |
| Mesa 9.x supports the OpenGL 3.1 specification. |
| |
| 1.2 Does Mesa support/use graphics hardware? |
| -------------------------------------------- |
| |
| Yes. Specifically, Mesa serves as the OpenGL core for the open-source |
| DRI drivers for X.org. |
| |
| - See the `DRI website <https://dri.freedesktop.org/>`__ for more |
| information. |
| - See `01.org <https://01.org/linuxgraphics>`__ for more information |
| about Intel drivers. |
| - See `nouveau.freedesktop.org <https://nouveau.freedesktop.org>`__ for |
| more information about Nouveau drivers. |
| - See |
| `www.x.org/wiki/RadeonFeature <https://www.x.org/wiki/RadeonFeature>`__ |
| for more information about Radeon drivers. |
| |
| 1.3 What purpose does Mesa serve today? |
| --------------------------------------- |
| |
| Hardware-accelerated OpenGL implementations are available for most |
| popular operating systems today. Still, Mesa serves at least these |
| purposes: |
| |
| - Mesa is used as the core of the open-source X.org DRI hardware |
| drivers. |
| - Mesa is quite portable and allows OpenGL to be used on systems that |
| have no other OpenGL solution. |
| - Software rendering with Mesa serves as a reference for validating the |
| hardware drivers. |
| - A software implementation of OpenGL is useful for experimentation, |
| such as testing new rendering techniques. |
| - Mesa can render images with deep color channels: 16-bit integer and |
| 32-bit floating point color channels are supported. This capability |
| is only now appearing in hardware. |
| - Mesa's internal limits (max lights, clip planes, texture size, etc) |
| can be changed for special needs (hardware limits are hard to |
| overcome). |
| |
| 1.4 What's the difference between "Stand-Alone" Mesa and the DRI drivers? |
| ------------------------------------------------------------------------- |
| |
| *Stand-alone Mesa* is the original incarnation of Mesa. On systems |
| running the X Window System it does all its rendering through the Xlib |
| API: |
| |
| - The GLX API is supported, but it's really just an emulation of the |
| real thing. |
| - The GLX wire protocol is not supported and there's no OpenGL |
| extension loaded by the X server. |
| - There is no hardware acceleration. |
| - The OpenGL library, ``libGL.so``, contains everything (the |
| programming API, the GLX functions and all the rendering code). |
| |
| Alternately, Mesa acts as the core for a number of OpenGL hardware |
| drivers within the DRI (Direct Rendering Infrastructure): |
| |
| - The ``libGL.so`` library provides the GL and GLX API functions, a GLX |
| protocol encoder, and a device driver loader. |
| - The device driver modules (such as ``r200_dri.so``) contain a |
| built-in copy of the core Mesa code. |
| - The X server loads the GLX module. The GLX module decodes incoming |
| GLX protocol and dispatches the commands to a rendering module. For |
| the DRI, this module is basically a software Mesa renderer. |
| |
| 1.5 How do I upgrade my DRI installation to use a new Mesa release? |
| ------------------------------------------------------------------- |
| |
| This wasn't easy in the past. Now, the DRI drivers are included in the |
| Mesa tree and can be compiled separately from the X server. Just follow |
| the Mesa :doc:`compilation instructions <install>`. |
| |
| 1.6 Are there other open-source implementations of OpenGL? |
| ---------------------------------------------------------- |
| |
| Yes, SGI's `OpenGL Sample Implementation |
| (SI) <http://web.archive.org/web/20171010115110_/http://oss.sgi.com/projects/ogl-sample/index.html>`__ |
| is available. The SI was written during the time that OpenGL was |
| originally designed. Unfortunately, development of the SI has stagnated. |
| Mesa is much more up to date with modern features and extensions. |
| |
| `Vincent <https://sourceforge.net/projects/ogl-es/>`__ is an open-source |
| implementation of OpenGL ES for mobile devices. |
| |
| `miniGL <http://web.archive.org/web/20130830162848/http://www.dsbox.com/minigl.html>`__ |
| is a subset of OpenGL for PalmOS devices. The website is gone, but the |
| source code can still be found on |
| `sourceforge.net <https://sourceforge.net/projects/minigl/>`__. |
| |
| `TinyGL <http://bellard.org/TinyGL/>`__ is a subset of OpenGL. |
| |
| `SoftGL <https://sourceforge.net/projects/softgl/>`__ is an OpenGL |
| subset for mobile devices. |
| |
| `Chromium <http://chromium.sourceforge.net/>`__ isn't a conventional |
| OpenGL implementation (it's layered upon OpenGL), but it does export the |
| OpenGL API. It allows tiled rendering, sort-last rendering, etc. |
| |
| `ClosedGL <http://www.ticalc.org/archives/files/fileinfo/361/36173.html>`__ |
| is an OpenGL subset library for TI graphing calculators. |
| |
| There may be other open OpenGL implementations, but Mesa is the most |
| popular and feature-complete. |
| |
| 2. Compilation and Installation Problems |
| ---------------------------------------- |
| |
| 2.1 What's the easiest way to install Mesa? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| If you're using a Linux-based system, your distro CD most likely already |
| has Mesa packages (like RPM or DEB) which you can easily install. |
| |
| 2.2 I get undefined symbols such as bgnpolygon, v3f, etc... |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Your application is written in IRIS GL, not OpenGL. IRIS GL was the |
| predecessor to OpenGL and is a different thing (almost) entirely. Mesa's |
| not the solution. |
| |
| 2.3 Where is the GLUT library? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| GLUT (OpenGL Utility Toolkit) is no longer in the separate |
| ``MesaGLUT-x.y.z.tar.gz`` file. If you don't already have GLUT |
| installed, you should grab |
| `freeglut <http://freeglut.sourceforge.net/>`__. |
| |
| 2.4 Where is the GLw library? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| GLw (OpenGL widget library) is now available from a separate `git |
| repository <https://gitlab.freedesktop.org/mesa/glw>`__. Unless you're |
| using very old Xt/Motif applications with OpenGL, you shouldn't need it. |
| |
| 2.5 What's the proper place for the libraries and headers? |
| ---------------------------------------------------------- |
| |
| On Linux-based systems you'll want to follow the `Linux |
| ABI <https://www.khronos.org/registry/OpenGL/ABI/>`__ standard. |
| Basically you'll want the following: |
| |
| ``/usr/include/GL/gl.h`` |
| the main OpenGL header |
| ``/usr/include/GL/glu.h`` |
| the OpenGL GLU (utility) header |
| ``/usr/include/GL/glx.h`` |
| the OpenGL GLX header |
| ``/usr/include/GL/glext.h`` |
| the OpenGL extensions header |
| ``/usr/include/GL/glxext.h`` |
| the OpenGL GLX extensions header |
| ``/usr/include/GL/osmesa.h`` |
| the Mesa off-screen rendering header |
| ``/usr/lib/libGL.so`` |
| a symlink to ``libGL.so.1`` |
| ``/usr/lib/libGL.so.1`` |
| a symlink to ``libGL.so.1.xyz`` |
| ``/usr/lib/libGL.so.xyz`` |
| the actual OpenGL/Mesa library. xyz denotes the Mesa version number. |
| |
| When configuring Mesa, there are three meson options that affect the |
| install location that you should take care with: ``--prefix``, |
| ``--libdir``, and ``-D dri-drivers-path``. To install Mesa into the |
| system location where it will be available for all programs to use, set |
| ``--prefix=/usr``. Set ``--libdir`` to where your Linux distribution |
| installs system libraries, usually either ``/usr/lib`` or |
| ``/usr/lib64``. Set ``-D dri-drivers-path`` to the directory where your |
| Linux distribution installs DRI drivers. To find your system's DRI |
| driver directory, try executing ``find /usr -type d -name dri``. For |
| example, if the ``find`` command listed ``/usr/lib64/dri``, then set |
| ``-D dri-drivers-path=/usr/lib64/dri``. |
| |
| After determining the correct values for the install location, configure |
| Mesa with |
| ``meson configure --prefix=/usr --libdir=xxx -D dri-drivers-path=xxx`` |
| and then install with ``sudo ninja install``. |
| |
| 3. Runtime / Rendering Problems |
| ------------------------------- |
| |
| 3.1 Rendering is slow / why isn't my graphics hardware being used? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| If Mesa can't use its hardware accelerated drivers it falls back on one |
| of its software renderers. (e.g. classic swrast, softpipe or llvmpipe) |
| |
| You can run the ``glxinfo`` program to learn about your OpenGL library. |
| Look for the ``OpenGL vendor`` and ``OpenGL renderer`` values. That will |
| identify who's OpenGL library with which driver you're using and what |
| sort of hardware it has detected. |
| |
| If you're using a hardware accelerated driver you want |
| ``direct rendering: Yes``. |
| |
| If your DRI-based driver isn't working, go to the `DRI |
| website <https://dri.freedesktop.org/>`__ for trouble-shooting |
| information. |
| |
| 3.2 I'm seeing errors in depth (Z) buffering. Why? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Make sure the ratio of the far to near clipping planes isn't too great. |
| Look |
| `here <https://www.opengl.org/archives/resources/faq/technical/depthbuffer.htm#0040>`__ |
| for details. |
| |
| Mesa uses a 16-bit depth buffer by default which is smaller and faster |
| to clear than a 32-bit buffer but not as accurate. If you need a deeper |
| you can modify the parameters to ``glXChooseVisual`` in your code. |
| |
| 3.3 Why Isn't depth buffering working at all? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Be sure you're requesting a depth buffered-visual. If you set the |
| ``MESA_DEBUG`` environment variable it will warn you about trying to |
| enable depth testing when you don't have a depth buffer. |
| |
| Specifically, make sure ``glutInitDisplayMode`` is being called with |
| ``GLUT_DEPTH`` or ``glXChooseVisual`` is being called with a non-zero |
| value for ``GLX_DEPTH_SIZE``. |
| |
| This discussion applies to stencil buffers, accumulation buffers and |
| alpha channels too. |
| |
| 3.4 Why does ``glGetString()`` always return ``NULL``? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Be sure you have an active/current OpenGL rendering context before |
| calling ``glGetString``. |
| |
| 3.5 ``GL_POINTS`` and ``GL_LINES`` don't touch the right pixels |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| If you're trying to draw a filled region by using ``GL_POINTS`` or |
| ``GL_LINES`` and seeing holes or gaps it's because of a float-to-int |
| rounding problem. But this is not a bug. See Appendix H of the OpenGL |
| Programming Guide - "OpenGL Correctness Tips". Basically, applying a |
| translation of (0.375, 0.375, 0.0) to your coordinates will fix the |
| problem. |
| |
| 4. Developer Questions |
| ---------------------- |
| |
| 4.1 How can I contribute? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| First, join the :doc:`mesa-dev mailing list <lists>`. That's where |
| Mesa development is discussed. |
| |
| The `OpenGL Specification <https://www.opengl.org/documentation>`__ is |
| the bible for OpenGL implementation work. You should read it. |
| |
| Most of the Mesa development work involves implementing new OpenGL |
| extensions, writing hardware drivers (for the DRI), and code |
| optimization. |
| |
| 4.2 How do I write a new device driver? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Unfortunately, writing a device driver isn't easy. It requires detailed |
| understanding of OpenGL, the Mesa code, and your target |
| hardware/operating system. 3D graphics are not simple. |
| |
| The best way to get started is to use an existing driver as your |
| starting point. For a classic hardware driver, the i965 driver is a good |
| example. For a Gallium3D hardware driver, the r300g, r600g and the i915g |
| are good examples. |
| |
| The DRI website has more information about writing hardware drivers. The |
| process isn't well document because the Mesa driver interface changes |
| over time, and we seldom have spare time for writing documentation. That |
| being said, many people have managed to figure out the process. |
| |
| Joining the appropriate mailing lists and asking questions (and |
| searching the archives) is a good way to get information. |
| |
| 4.3 Why isn't ``GL_EXT_texture_compression_s3tc`` implemented in Mesa? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Oh but it is! Prior to 2nd October 2017, the Mesa project did not |
| include S3TC support due to intellectual property (IP) and/or patent |
| issues around the S3TC algorithm. |
| |
| As of Mesa 17.3.0, Mesa now officially supports S3TC, as the patent has |
| expired. |
| |
| In versions prior to this, a 3rd party `plug-in |
| library <https://dri.freedesktop.org/wiki/S3TC>`__ was required. |