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docs: rewrite the OSMesa info / instructions

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Reviewed-by: José Fonseca <jfonseca@vmware.com>
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Brian Paul 2013-03-11 18:31:22 -06:00
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docs/osmesa.html
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@ -18,77 +18,62 @@
<p>
Mesa's off-screen rendering interface is used for rendering into
user-allocated blocks of memory.
Mesa's off-screen interface is used for rendering into user-allocated memory
without any sort of window system or operating system dependencies.
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
The OSMesa 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>
The OSMesa interface may be used with any of three software renderers:
</p>
<ol>
<li>llvmpipe - this is the high-performance Gallium LLVM driver
<li>softpipe - this it the reference Gallium software driver
<li>swrast - this is the legacy Mesa software rasterizer
</ol>
<p>
There are several examples of OSMesa in the mesa/demos repository.
</p>
<h2>Deep color channels</h2>
<h1>Building OSMesa</h1>
<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>
Configure and build Mesa with something like:
<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
configure --enable-osmesa --disable-driglx-direct --disable-dri --with-gallium-drivers=swrast
make
</pre>
<p>
To build Mesa/OSMesa for 32, 16 and 8-bit color channel support:
Make sure you have LLVM installed first if you want to use the llvmpipe driver.
</p>
<p>
When the build is complete you should find:
</p>
<pre>
make realclean
make linux-osmesa32
lib/libOSMesa.so (swrast-based OSMesa)
lib/gallium/libOSMsea.so (gallium-based OSMesa)
</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.
Set your LD_LIBRARY_PATH to point to one directory or the other to select
the library you want to use.
</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.
When you link your application, link with -lOSMesa
</p>
</div>