README.txt
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3Notes about the EGL library:
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6The EGL code here basically consists of two things:
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81. An EGL API dispatcher. This directly routes all the eglFooBar() API
9 calls into driver-specific functions.
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112. Fallbacks for EGL API functions. A driver _could_ implement all the
12 EGL API calls from scratch. But in many cases, the fallbacks provided
13 in libEGL (such as eglChooseConfig()) will do the job.
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17Bootstrapping:
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19When the apps calls eglOpenDisplay() a device driver is selected and loaded
20(look for dlsym() or LoadLibrary() in egldriver.c).
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22The driver's _eglMain() function is then called. This driver function
23allocates, initializes and returns a new _EGLDriver object (usually a
24subclass of that type).
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26As part of initialization, the dispatch table in _EGLDriver->API must be
27populated with all the EGL entrypoints. Typically, _eglInitDriverFallbacks()
28can be used to plug in default/fallback functions. Some functions like
29driver->API.Initialize and driver->API.Terminate _must_ be implemented
30with driver-specific code (no default/fallback function is possible).
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33A bit later, the app will call eglInitialize(). This will get routed
34to the driver->API.Initialize() function. Any additional driver
35initialization that wasn't done in _eglMain() should be done at this
36point. Typically, this will involve setting up visual configs, etc.
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40Special Functions:
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42Certain EGL functions _must_ be implemented by the driver. This includes:
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44eglCreateContext
45eglCreateWindowSurface
46eglCreatePixmapSurface
47eglCreatePBufferSurface
48eglMakeCurrent
49eglSwapBuffers
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51Most of the EGLConfig-related functions can be implemented with the
52defaults/fallbacks. Same thing for the eglGet/Query functions.
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57Teardown:
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59When eglTerminate() is called, the driver->API.Terminate() function is
60called. The driver should clean up after itself. eglTerminate() will
61then close/unload the driver (shared library).
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66Subclassing:
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68The internal libEGL data structures such as _EGLDisplay, _EGLContext,
69_EGLSurface, etc should be considered base classes from which drivers
70will derive subclasses.
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