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Notes about the EGL library:
The EGL code here basically consists of two things:
1. An EGL API dispatcher. This directly routes all the eglFooBar() API
calls into driver-specific functions.
2. Fallbacks for EGL API functions. A driver _could_ implement all the
EGL API calls from scratch. But in many cases, the fallbacks provided
in libEGL (such as eglChooseConfig()) will do the job.
Bootstrapping:
When the apps calls eglOpenDisplay() a device driver is selected and loaded
(look for dlsym() or LoadLibrary() in egldriver.c).
The driver's _eglMain() function is then called. This driver function
allocates, initializes and returns a new _EGLDriver object (usually a
subclass of that type).
As part of initialization, the dispatch table in _EGLDriver->API must be
populated with all the EGL entrypoints. Typically, _eglInitDriverFallbacks()
can be used to plug in default/fallback functions. Some functions like
driver->API.Initialize and driver->API.Terminate _must_ be implemented
with driver-specific code (no default/fallback function is possible).
A bit later, the app will call eglInitialize(). This will get routed
to the driver->API.Initialize() function. Any additional driver
initialization that wasn't done in _eglMain() should be done at this
point. Typically, this will involve setting up visual configs, etc.
Special Functions:
Certain EGL functions _must_ be implemented by the driver. This includes:
eglCreateContext
eglCreateWindowSurface
eglCreatePixmapSurface
eglCreatePBufferSurface
eglMakeCurrent
eglSwapBuffers
Most of the EGLConfig-related functions can be implemented with the
defaults/fallbacks. Same thing for the eglGet/Query functions.
Teardown:
When eglTerminate() is called, the driver->API.Terminate() function is
called. The driver should clean up after itself. eglTerminate() will
then close/unload the driver (shared library).
Subclassing:
The internal libEGL data structures such as _EGLDisplay, _EGLContext,
_EGLSurface, etc should be considered base classes from which drivers
will derive subclasses.
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