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https://gitee.com/openharmony/third_party_mesa3d
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89 lines
2.3 KiB
HTML
89 lines
2.3 KiB
HTML
<HTML>
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<TITLE>Off-screen Rendering</TITLE>
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<link rel="stylesheet" type="text/css" href="mesa.css"></head>
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<BODY>
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<H1>Off-screen Rendering</H1>
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<p>
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Mesa's off-screen rendering interface is used for rendering into
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user-allocated blocks of memory.
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That is, the GL_FRONT colorbuffer is actually a buffer in main memory,
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rather than a window on your display.
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There are no window system or operating system dependencies.
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One potential application is to use Mesa as an off-line, batch-style renderer.
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</p>
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<p>
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The <B>OSMesa</B> API provides three basic functions for making off-screen
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renderings: OSMesaCreateContext(), OSMesaMakeCurrent(), and
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OSMesaDestroyContext(). See the Mesa/include/GL/osmesa.h header for
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more information about the API functions.
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</p>
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<p>
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There are several examples of OSMesa in the <code>progs/osdemos/</code>
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directory.
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</p>
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<H2>Deep color channels</H2>
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<p>
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For some applications 8-bit color channels don't have sufficient
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precision.
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OSMesa supports 16-bit and 32-bit color channels through the OSMesa interface.
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When using 16-bit channels, channels are GLushorts and RGBA pixels occupy
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8 bytes.
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When using 32-bit channels, channels are GLfloats and RGBA pixels occupy
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16 bytes.
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</p>
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<p>
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Before version 6.5.1, Mesa had to be recompiled to support exactly
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one of 8, 16 or 32-bit channels.
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With Mesa 6.5.1, Mesa can be compiled for either 8, 16 or 32-bit channels
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and render into any of the smaller size channels.
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For example, if Mesa's compiled for 32-bit channels, you can also render
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16 and 8-bit channel images.
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</p>
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<p>
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To build Mesa/OSMesa for 16 and 8-bit color channel support:
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<pre>
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make realclean
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make linux-osmesa16
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</pre>
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<p>
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To build Mesa/OSMesa for 32, 16 and 8-bit color channel support:
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<pre>
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make realclean
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make linux-osmesa32
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</pre>
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<p>
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You'll wind up with a library named libOSMesa16.so or libOSMesa32.so.
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Otherwise, most Mesa configurations build an 8-bit/channel libOSMesa.so library
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by default.
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</p>
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<p>
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If performance is important, compile Mesa for the channel size you're
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most interested in.
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</p>
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<p>
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If you need to compile on a non-Linux platform, copy Mesa/configs/linux-osmesa16
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to a new config file and edit it as needed. Then, add the new config name to
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the top-level Makefile. Send a patch to the Mesa developers too, if you're
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inclined.
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</p>
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</BODY>
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</HTML>
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