1<HTML> 2 3<TITLE>Off-screen Rendering</TITLE> 4 5<link rel="stylesheet" type="text/css" href="mesa.css"></head> 6 7<BODY> 8 9<H1>Off-screen Rendering</H1> 10 11 12<p> 13Mesa's off-screen rendering interface is used for rendering into 14user-allocated blocks of memory. 15That is, the GL_FRONT colorbuffer is actually a buffer in main memory, 16rather than a window on your display. 17There are no window system or operating system dependencies. 18One potential application is to use Mesa as an off-line, batch-style renderer. 19</p> 20 21<p> 22The <B>OSMesa</B> API provides three basic functions for making off-screen 23renderings: OSMesaCreateContext(), OSMesaMakeCurrent(), and 24OSMesaDestroyContext(). See the Mesa/include/GL/osmesa.h header for 25more information about the API functions. 26</p> 27 28<p> 29There are several examples of OSMesa in the <code>progs/osdemos/</code> 30directory. 31</p> 32 33 34<H2>Deep color channels</H2> 35 36<p> 37For some applications 8-bit color channels don't have sufficient 38precision. 39OSMesa supports 16-bit and 32-bit color channels through the OSMesa interface. 40When using 16-bit channels, channels are GLushorts and RGBA pixels occupy 418 bytes. 42When using 32-bit channels, channels are GLfloats and RGBA pixels occupy 4316 bytes. 44</p> 45 46<p> 47Before version 6.5.1, Mesa had to be recompiled to support exactly 48one of 8, 16 or 32-bit channels. 49With Mesa 6.5.1, Mesa can be compiled for either 8, 16 or 32-bit channels 50and render into any of the smaller size channels. 51For example, if Mesa's compiled for 32-bit channels, you can also render 5216 and 8-bit channel images. 53</p> 54 55<p> 56To build Mesa/OSMesa for 16 and 8-bit color channel support: 57<pre> 58 make realclean 59 make linux-osmesa16 60</pre> 61 62<p> 63To build Mesa/OSMesa for 32, 16 and 8-bit color channel support: 64<pre> 65 make realclean 66 make linux-osmesa32 67</pre> 68 69<p> 70You'll wind up with a library named libOSMesa16.so or libOSMesa32.so. 71Otherwise, most Mesa configurations build an 8-bit/channel libOSMesa.so library 72by default. 73</p> 74 75<p> 76If performance is important, compile Mesa for the channel size you're 77most interested in. 78</p> 79 80<p> 81If you need to compile on a non-Linux platform, copy Mesa/configs/linux-osmesa16 82to a new config file and edit it as needed. Then, add the new config name to 83the top-level Makefile. Send a patch to the Mesa developers too, if you're 84inclined. 85</p> 86 87</BODY> 88</HTML> 89