src/egl/main/README.txt

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   2
   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.
  14
  15
  16
  17 Bootstrapping:
  18
  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.  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 Shortly after, the driver->API.Initialize() function is executed.  Any additional
  34 driver initialization that wasn't done in the driver entry point should be
  35 done at this point.  Typically, this will involve setting up visual configs, etc.
  36
  37
  38
  39 Special Functions:
  40
  41 Certain EGL functions _must_ be implemented by the driver.  This includes:
  42
  43 eglCreateContext
  44 eglCreateWindowSurface
  45 eglCreatePixmapSurface
  46 eglCreatePBufferSurface
  47 eglMakeCurrent
  48 eglSwapBuffers
  49
  50 Most of the EGLConfig-related functions can be implemented with the
  51 defaults/fallbacks.  Same thing for the eglGet/Query functions.
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  53
  54
  55
  56 Teardown:
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  58 When eglTerminate() is called, the driver->API.Terminate() function is
  59 called.  The driver should clean up after itself.  eglTerminate() will
  60 then close/unload the driver (shared library).
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  62
  63
  64
  65 Subclassing:
  66
  67 The internal libEGL data structures such as _EGLDisplay, _EGLContext,
  68 _EGLSurface, etc should be considered base classes from which drivers
  69 will derive subclasses.
  70