docs/faq.rst - platform/external/mesa3d - Gitiles

 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...
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 You're 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.
	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...
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	You're 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.