1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2 <html lang="en"> 3 <head> 4 <meta http-equiv="content-type" content="text/html; charset=utf-8"> 5 <title>Off-screen Rendering</title> 6 <link rel="stylesheet" type="text/css" href="mesa.css"> 7 </head> 8 <body> 9 10 <h1>Off-screen Rendering</h1> 11 12 13 <p> 14 Mesa's off-screen rendering interface is used for rendering into 15 user-allocated blocks of memory. 16 That is, the GL_FRONT colorbuffer is actually a buffer in main memory, 17 rather than a window on your display. 18 There are no window system or operating system dependencies. 19 One potential application is to use Mesa as an off-line, batch-style renderer. 20 </p> 21 22 <p> 23 The <b>OSMesa</b> API provides three basic functions for making off-screen 24 renderings: OSMesaCreateContext(), OSMesaMakeCurrent(), and 25 OSMesaDestroyContext(). See the Mesa/include/GL/osmesa.h header for 26 more information about the API functions. 27 </p> 28 29 <p> 30 There are several examples of OSMesa in the <code>progs/osdemos/</code> 31 directory. 32 </p> 33 34 35 <h2>Deep color channels</h2> 36 37 <p> 38 For some applications 8-bit color channels don't have sufficient 39 precision. 40 OSMesa supports 16-bit and 32-bit color channels through the OSMesa interface. 41 When using 16-bit channels, channels are GLushorts and RGBA pixels occupy 42 8 bytes. 43 When using 32-bit channels, channels are GLfloats and RGBA pixels occupy 44 16 bytes. 45 </p> 46 47 <p> 48 Before version 6.5.1, Mesa had to be recompiled to support exactly 49 one of 8, 16 or 32-bit channels. 50 With Mesa 6.5.1, Mesa can be compiled for either 8, 16 or 32-bit channels 51 and render into any of the smaller size channels. 52 For example, if Mesa's compiled for 32-bit channels, you can also render 53 16 and 8-bit channel images. 54 </p> 55 56 <p> 57 To build Mesa/OSMesa for 16 and 8-bit color channel support: 58 <pre> 59 make realclean 60 make linux-osmesa16 61 </pre> 62 63 <p> 64 To build Mesa/OSMesa for 32, 16 and 8-bit color channel support: 65 <pre> 66 make realclean 67 make linux-osmesa32 68 </pre> 69 70 <p> 71 You'll wind up with a library named libOSMesa16.so or libOSMesa32.so. 72 Otherwise, most Mesa configurations build an 8-bit/channel libOSMesa.so library 73 by default. 74 </p> 75 76 <p> 77 If performance is important, compile Mesa for the channel size you're 78 most interested in. 79 </p> 80 81 <p> 82 If you need to compile on a non-Linux platform, copy Mesa/configs/linux-osmesa16 83 to a new config file and edit it as needed. Then, add the new config name to 84 the top-level Makefile. Send a patch to the Mesa developers too, if you're 85 inclined. 86 </p> 87 88 </body> 89 </html> 90
