mirror of https://gitlab.freedesktop.org/mesa/mesa
72 lines
2.0 KiB
Plaintext
72 lines
2.0 KiB
Plaintext
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Notes about the EGL library:
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The EGL code here basically consists of two things:
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1. An EGL API dispatcher. This directly routes all the eglFooBar() API
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calls into driver-specific functions.
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2. Fallbacks for EGL API functions. A driver _could_ implement all the
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EGL API calls from scratch. But in many cases, the fallbacks provided
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in libEGL (such as eglChooseConfig()) will do the job.
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Bootstrapping:
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When the apps calls eglOpenDisplay() a device driver is selected and loaded
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(look for dlsym() or LoadLibrary() in egldriver.c).
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The driver's _eglMain() function is then called. This driver function
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allocates, initializes and returns a new _EGLDriver object (usually a
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subclass of that type).
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As part of initialization, the dispatch table in _EGLDriver->API must be
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populated with all the EGL entrypoints. Typically, _eglInitDriverFallbacks()
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can be used to plug in default/fallback functions. Some functions like
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driver->API.Initialize and driver->API.Terminate _must_ be implemented
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with driver-specific code (no default/fallback function is possible).
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A bit later, the app will call eglInitialize(). This will get routed
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to the driver->API.Initialize() function. Any additional driver
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initialization that wasn't done in _eglMain() should be done at this
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point. Typically, this will involve setting up visual configs, etc.
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Special Functions:
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Certain EGL functions _must_ be implemented by the driver. This includes:
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eglCreateContext
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eglCreateWindowSurface
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eglCreatePixmapSurface
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eglCreatePBufferSurface
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eglMakeCurrent
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eglSwapBuffers
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Most of the EGLConfig-related functions can be implemented with the
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defaults/fallbacks. Same thing for the eglGet/Query functions.
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Teardown:
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When eglTerminate() is called, the driver->API.Terminate() function is
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called. The driver should clean up after itself. eglTerminate() will
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then close/unload the driver (shared library).
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Subclassing:
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The internal libEGL data structures such as _EGLDisplay, _EGLContext,
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_EGLSurface, etc should be considered base classes from which drivers
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will derive subclasses.
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