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5  <title>Off-screen Rendering</title>
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9
10<h1>Off-screen Rendering</h1>
11
12
13<p>
14Mesa's off-screen rendering interface is used for rendering into
15user-allocated blocks of memory.
16That is, the GL_FRONT colorbuffer is actually a buffer in main memory,
17rather than a window on your display.
18There are no window system or operating system dependencies.
19One potential application is to use Mesa as an off-line, batch-style renderer.
20</p>
21
22<p>
23The <b>OSMesa</b> API provides three basic functions for making off-screen
24renderings: OSMesaCreateContext(), OSMesaMakeCurrent(), and
25OSMesaDestroyContext().  See the Mesa/include/GL/osmesa.h header for
26more information about the API functions.
27</p>
28
29<p>
30There are several examples of OSMesa in the <code>progs/osdemos/</code>
31directory.
32</p>
33
34
35<h2>Deep color channels</h2>
36
37<p>
38For some applications 8-bit color channels don't have sufficient
39precision.
40OSMesa supports 16-bit and 32-bit color channels through the OSMesa interface.
41When using 16-bit channels, channels are GLushorts and RGBA pixels occupy
428 bytes.
43When using 32-bit channels, channels are GLfloats and RGBA pixels occupy
4416 bytes.
45</p>
46
47<p>
48Before version 6.5.1, Mesa had to be recompiled to support exactly
49one of 8, 16 or 32-bit channels.
50With Mesa 6.5.1, Mesa can be compiled for either 8, 16 or 32-bit channels
51and render into any of the smaller size channels.
52For example, if Mesa's compiled for 32-bit channels, you can also render
5316 and 8-bit channel images.
54</p>
55
56<p>
57To build Mesa/OSMesa for 16 and 8-bit color channel support:
58<pre>
59      make realclean
60      make linux-osmesa16
61</pre>
62
63<p>
64To build Mesa/OSMesa for 32, 16 and 8-bit color channel support:
65<pre>
66      make realclean
67      make linux-osmesa32
68</pre>
69
70<p>
71You'll wind up with a library named libOSMesa16.so or libOSMesa32.so.
72Otherwise, most Mesa configurations build an 8-bit/channel libOSMesa.so library
73by default.
74</p>
75
76<p>
77If performance is important, compile Mesa for the channel size you're
78most interested in.
79</p>
80
81<p>
82If you need to compile on a non-Linux platform, copy Mesa/configs/linux-osmesa16
83to a new config file and edit it as needed.  Then, add the new config name to
84the top-level Makefile.  Send a patch to the Mesa developers too, if you're
85inclined.
86</p>
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