1
2
3Notes about the EGL library:
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5
6The EGL code here basically consists of two things:
7
81. An EGL API dispatcher.  This directly routes all the eglFooBar() API
9   calls into driver-specific functions.
10
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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15
16
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).
21
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).
25
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).
31
32
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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38
39
40Special Functions:
41
42Certain EGL functions _must_ be implemented by the driver.  This includes:
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44eglCreateContext
45eglCreateWindowSurface
46eglCreatePixmapSurface
47eglCreatePBufferSurface
48eglMakeCurrent
49eglSwapBuffers
50
51Most of the EGLConfig-related functions can be implemented with the
52defaults/fallbacks.  Same thing for the eglGet/Query functions.
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54
55
56
57Teardown:
58
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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63
64
65
66Subclassing:
67
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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72