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| -rw-r--r-- | src/egl/main/README.txt | 71 |
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diff --git a/src/egl/main/README.txt b/src/egl/main/README.txt new file mode 100644 index 0000000000..b3d253dd13 --- /dev/null +++ b/src/egl/main/README.txt @@ -0,0 +1,71 @@ + + +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. + |