workbench/libs/mesa/docs/osmesa.html

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   3 <TITLE>Off-screen Rendering</TITLE>
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   9 <H1>Off-screen Rendering</H1>
  10
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  12 <p>
  13 Mesa's off-screen rendering interface is used for rendering into
  14 user-allocated blocks of memory.
  15 That is, the GL_FRONT colorbuffer is actually a buffer in main memory,
  16 rather than a window on your display.
  17 There are no window system or operating system dependencies.
  18 One potential application is to use Mesa as an off-line, batch-style renderer.
  19 </p>
  20
  21 <p>
  22 The <B>OSMesa</B> API provides three basic functions for making off-screen
  23 renderings: OSMesaCreateContext(), OSMesaMakeCurrent(), and
  24 OSMesaDestroyContext().  See the Mesa/include/GL/osmesa.h header for
  25 more information about the API functions.
  26 </p>
  27
  28 <p>
  29 There are several examples of OSMesa in the <code>progs/osdemos/</code>
  30 directory.
  31 </p>
  32
  33
  34 <H2>Deep color channels</H2>
  35
  36 <p>
  37 For some applications 8-bit color channels don't have sufficient
  38 precision.
  39 OSMesa supports 16-bit and 32-bit color channels through the OSMesa interface.
  40 When using 16-bit channels, channels are GLushorts and RGBA pixels occupy
  41 8 bytes.
  42 When using 32-bit channels, channels are GLfloats and RGBA pixels occupy
  43 16 bytes.
  44 </p>
  45
  46 <p>
  47 Before version 6.5.1, Mesa had to be recompiled to support exactly
  48 one of 8, 16 or 32-bit channels.
  49 With Mesa 6.5.1, Mesa can be compiled for either 8, 16 or 32-bit channels
  50 and render into any of the smaller size channels.
  51 For example, if Mesa's compiled for 32-bit channels, you can also render
  52 16 and 8-bit channel images.
  53 </p>
  54
  55 <p>
  56 To build Mesa/OSMesa for 16 and 8-bit color channel support:
  57 <pre>
  58       make realclean
  59       make linux-osmesa16
  60 </pre>
  61
  62 <p>
  63 To build Mesa/OSMesa for 32, 16 and 8-bit color channel support:
  64 <pre>
  65       make realclean
  66       make linux-osmesa32
  67 </pre>
  68
  69 <p>
  70 You'll wind up with a library named libOSMesa16.so or libOSMesa32.so.
  71 Otherwise, most Mesa configurations build an 8-bit/channel libOSMesa.so library
  72 by default.
  73 </p>
  74
  75 <p>
  76 If performance is important, compile Mesa for the channel size you're
  77 most interested in.
  78 </p>
  79
  80 <p>
  81 If you need to compile on a non-Linux platform, copy Mesa/configs/linux-osmesa16
  82 to a new config file and edit it as needed.  Then, add the new config name to
  83 the top-level Makefile.  Send a patch to the Mesa developers too, if you're
  84 inclined.
  85 </p>
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