src/egl/main/README.txt

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   3 Notes about the EGL library:
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   5
   6 The EGL code here basically consists of two things:
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   8 1. An EGL API dispatcher.  This directly routes all the eglFooBar() API
   9    calls into driver-specific functions.
  10
  11 2. 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
  17 Bootstrapping:
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  19 When the apps calls eglInitialize() a device driver is selected and loaded
  20 (look for _eglAddDrivers() and _eglLoadModule() in egldriver.c).
  21
  22 The built-in driver's entry point function is then called and given
  23 a freshly allocated and initialised _EGLDriver, with default fallback
  24 entrypoints set.
  25
  26 As part of initialization, the dispatch table in _EGLDriver->API must be
  27 populated with all the EGL entrypoints. Some functions like
  28 driver->API.Initialize and driver->API.Terminate _must_ be implemented
  29 with driver-specific code (no default/fallback function is possible).
  30
  31
  32 Shortly after, the driver->API.Initialize() function is executed.  Any additional
  33 driver initialization that wasn't done in the driver entry point should be
  34 done at this point.  Typically, this will involve setting up visual configs, etc.
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  36
  37
  38 Special Functions:
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  40 Certain EGL functions _must_ be implemented by the driver.  This includes:
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  42 eglCreateContext
  43 eglCreateWindowSurface
  44 eglCreatePixmapSurface
  45 eglCreatePBufferSurface
  46 eglMakeCurrent
  47 eglSwapBuffers
  48
  49 Most of the EGLConfig-related functions can be implemented with the
  50 defaults/fallbacks.  Same thing for the eglGet/Query functions.
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  54
  55 Teardown:
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  57 When eglTerminate() is called, the driver->API.Terminate() function is
  58 called.  The driver should clean up after itself.  eglTerminate() will
  59 then close/unload the driver (shared library).
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  64 Subclassing:
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  66 The internal libEGL data structures such as _EGLDisplay, _EGLContext,
  67 _EGLSurface, etc should be considered base classes from which drivers
  68 will derive subclasses.
  69