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 eglOpenDisplay() a device driver is selected and loaded
  20 (look for dlsym() or LoadLibrary() in egldriver.c).
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  22 The driver's _eglMain() function is then called.  This driver function
  23 allocates, initializes and returns a new _EGLDriver object (usually a
  24 subclass of that type).
  25
  26 As part of initialization, the dispatch table in _EGLDriver->API must be
  27 populated with all the EGL entrypoints.  Typically, _eglInitDriverFallbacks()
  28 can be used to plug in default/fallback functions.  Some functions like
  29 driver->API.Initialize and driver->API.Terminate _must_ be implemented
  30 with driver-specific code (no default/fallback function is possible).
  31
  32
  33 A bit later, the app will call eglInitialize().  This will get routed
  34 to the driver->API.Initialize() function.  Any additional driver
  35 initialization that wasn't done in _eglMain() should be done at this
  36 point.  Typically, this will involve setting up visual configs, etc.
  37
  38
  39
  40 Special Functions:
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  42 Certain EGL functions _must_ be implemented by the driver.  This includes:
  43
  44 eglCreateContext
  45 eglCreateWindowSurface
  46 eglCreatePixmapSurface
  47 eglCreatePBufferSurface
  48 eglMakeCurrent
  49 eglSwapBuffers
  50
  51 Most of the EGLConfig-related functions can be implemented with the
  52 defaults/fallbacks.  Same thing for the eglGet/Query functions.
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  56
  57 Teardown:
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  59 When eglTerminate() is called, the driver->API.Terminate() function is
  60 called.  The driver should clean up after itself.  eglTerminate() will
  61 then close/unload the driver (shared library).
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  63
  64
  65
  66 Subclassing:
  67
  68 The internal libEGL data structures such as _EGLDisplay, _EGLContext,
  69 _EGLSurface, etc should be considered base classes from which drivers
  70 will derive subclasses.
  71