1 2 3Notes about the EGL library: 4 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. 14 15 16 17Bootstrapping: 18 19When the apps calls eglInitialize() a device driver is selected and loaded 20(look for _eglAddDrivers() and _eglLoadModule() in egldriver.c). 21 22The built-in driver's entry point 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 33Shortly after, the driver->API.Initialize() function is executed. Any additional 34driver initialization that wasn't done in the driver entry point should be 35done at this point. Typically, this will involve setting up visual configs, etc. 36 37 38 39Special Functions: 40 41Certain EGL functions _must_ be implemented by the driver. This includes: 42 43eglCreateContext 44eglCreateWindowSurface 45eglCreatePixmapSurface 46eglCreatePBufferSurface 47eglMakeCurrent 48eglSwapBuffers 49 50Most of the EGLConfig-related functions can be implemented with the 51defaults/fallbacks. Same thing for the eglGet/Query functions. 52 53 54 55 56Teardown: 57 58When eglTerminate() is called, the driver->API.Terminate() function is 59called. The driver should clean up after itself. eglTerminate() will 60then close/unload the driver (shared library). 61 62 63 64 65Subclassing: 66 67The internal libEGL data structures such as _EGLDisplay, _EGLContext, 68_EGLSurface, etc should be considered base classes from which drivers 69will derive subclasses. 70 71