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