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<HTML>
<TITLE>Off-screen Rendering</TITLE>
<BODY text="#000000" bgcolor="#55bbff" link="#111188">
<H1>Off-screen Rendering</H1>
<p>
Mesa 1.2.4 introduced off-screen rendering, a facility for generating
3-D imagery without having to open a window on your display. Mesa's
simple off-screen rendering interface is completely operating system
and window system independent so programs which use off-screen
rendering should be very portable. This feature effectively
enables you to use Mesa as an off-line, batch-oriented renderer.
</p>
<p>
The "OSMesa" API provides 3 functions for making off-screen
renderings: OSMesaCreateContext(), OSMesaMakeCurrent(), and
OSMesaDestroyContext(). See the Mesa/include/GL/osmesa.h header for
more information. See the demos/osdemo.c file for an example program.
There is no facility for writing images to files. That's up to you.
</p>
<p>
If you want to generate large images (larger than 1280x1024) you'll
have to edit the src/config.h file to change MAX_WIDTH and MAX_HEIGHT
then recompile Mesa. Image size should only be limited by available
memory.
</p>
<H2>Deep color channels</H2>
<p>
For some applications 8-bit color channels don't have sufficient
accuracy (film and IBR, for example). If you're in this situation
you'll be happy to know that Mesa supports 16-bit and 32-bit color
channels through the OSMesa interface. When using 16-bit channels,
channels are GLushorts and pixels occupy 8 bytes. When using 32-bit
channels, channels are GLfloats and pixels occupy 16 bytes.
</p>
<p>
To build Mesa/OSMesa with 16-bit color channels:
<pre>
cd Mesa-4.x/src
make -f Makefile.X11 clean
make -f Makefile.OSMesa16 linux-osmesa16
</pre>
For 32-bit channels:
<pre>
cd Mesa-4.x/src
make -f Makefile.X11 clean
make -f Makefile.OSMesa16 linux-osmesa32
</pre>
<p>
If you're not using Linux, you can easily edit Make-config and add
an appropriate configuration.
</p>
<p>
The Mesa/tests/osdemo16.c file (available via CVS) demonstrates how
to use this feature.
</p>
<p>
BE WARNED: 16 and 32-bit channel support has not been exhaustively
tested and there may be some bugs. However, a number of people have
been using this feature successfully so it can't be too broken.
</p>
</BODY>
</HTML>
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