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<TITLE>Off-screen Rendering</TITLE>
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<H1>Off-screen Rendering</H1>
<p>
Mesa's off-screen rendering interface is used for rendering into
user-allocated blocks of memory.
That is, the GL_FRONT colorbuffer is actually a buffer in main memory,
rather than a window on your display.
There are no window system or operating system dependencies.
One potential application is to use Mesa as an off-line, batch-style renderer.
</p>
<p>
The <B>OSMesa</B> API provides three basic functions for making off-screen
renderings: OSMesaCreateContext(), OSMesaMakeCurrent(), and
OSMesaDestroyContext(). See the Mesa/include/GL/osmesa.h header for
more information about the API functions.
</p>
<p>
There are several examples of OSMesa in the <code>progs/osdemos/</code>
directory.
</p>
<H2>Deep color channels</H2>
<p>
For some applications 8-bit color channels don't have sufficient
precision.
OSMesa supports 16-bit and 32-bit color channels through the OSMesa interface.
When using 16-bit channels, channels are GLushorts and RGBA pixels occupy
8 bytes.
When using 32-bit channels, channels are GLfloats and RGBA pixels occupy
16 bytes.
</p>
<p>
Before version 6.5.1, Mesa had to be recompiled to support exactly
one of 8, 16 or 32-bit channels.
With Mesa 6.5.1, Mesa can be compiled for either 8, 16 or 32-bit channels
and render into any of the smaller size channels.
For example, if Mesa's compiled for 32-bit channels, you can also render
16 and 8-bit channel images.
</p>
<p>
To build Mesa/OSMesa for 16 and 8-bit color channel support:
<pre>
make realclean
make linux-osmesa16
</pre>
<p>
To build Mesa/OSMesa for 32, 16 and 8-bit color channel support:
<pre>
make realclean
make linux-osmesa32
</pre>
<p>
You'll wind up with a library named libOSMesa16.so or libOSMesa32.so.
Otherwise, most Mesa configurations build an 8-bit/channel libOSMesa.so library
by default.
</p>
<p>
If performance is important, compile Mesa for the channel size you're
most interested in.
</p>
<p>
If you need to compile on a non-Linux platform, copy Mesa/configs/linux-osmesa16
to a new config file and edit it as needed. Then, add the new config name to
the top-level Makefile. Send a patch to the Mesa developers too, if you're
inclined.
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