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+ <title>Off-screen Rendering</title>
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-<TITLE>Off-screen Rendering</TITLE>
+<div class="header">
+ <h1>The Mesa 3D Graphics Library</h1>
+</div>
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+<div class="content">
-<H1>Off-screen Rendering</H1>
+<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.
+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 "OSMesa" API provides 3 functions for making off-screen
+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. See the demos/osdemo.c file for an example program.
-There is no facility for writing images to files. That's up to you.
+more information about the API functions.
</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.
+There are several examples of OSMesa in the mesa/demos repository.
</p>
-<H2>Deep color channels</H2>
+<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>
- 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.
+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 with 16-bit color channels:
+To build Mesa/OSMesa for 16 and 8-bit color channel support:
<pre>
- cd Mesa-4.x/src
- make -f Makefile.X11 clean
- make -f Makefile.OSMesa16 linux-osmesa16
+ make realclean
+ make linux-osmesa16
</pre>
- For 32-bit channels:
+<p>
+To build Mesa/OSMesa for 32, 16 and 8-bit color channel support:
<pre>
- cd Mesa-4.x/src
- make -f Makefile.X11 clean
- make -f Makefile.OSMesa16 linux-osmesa32
+ make realclean
+ make linux-osmesa32
</pre>
<p>
-If you're not using Linux, you can easily edit Make-config and add
-an appropriate configuration.
+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>
-The Mesa/tests/osdemo16.c file (available via CVS) demonstrates how
-to use this feature.
+If performance is important, compile Mesa for the channel size you're
+most interested in.
</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.
+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.
</p>
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