OpenGL Interface Implementation

See OpenGL Interface for details on the publically-visible modules.

See ctypes Wrapper Generation for details on some of these modules are generated.

ctypes linkage

Most functions link to libGL.so (Linux), opengl32.dll (Windows) or OpenGL.framework (OS X). pyglet.gl.lib provides some helper types then imports linker functions for the appropriate platform: one of pyglet.gl.lib_agl, pyglet.gl.lib_glx, pyglet.gl.lib_wgl.

On any platform, the following steps are taken to link each function during import:

  1. Look in the appropriate library (e.g. libGL.so, libGLU.so, opengl32.dll, etc.) using cdll or windll.

  2. If not found, call wglGetProcAddress or glxGetProcAddress to try to resolve the function’s address dynamically. On OS X, skip this step.

  3. On Windows, this will fail if the context hasn’t been created yet. Create and return a proxy object WGLFunctionProxy which will try the same resolution again when the object is __call__‘d.

    The proxy object caches its result so that subsequent calls have only a single extra function-call overhead.

  4. If the function is still not found (either during import or proxy call), the function is replaced with MissingFunction (defined in pyglet.gl.lib), which raises an exception. The exception message details the name of the function, and optionally the name of the extension it requires and any alternative functions that can be used.

    The extension required is currently guessed by gengl.py based on nearby #ifndef declarations, it is occasionally wrong.

    The suggestion list is not currently used, but is intended to be implemented such that calling, for example, glCreateShader on an older driver suggests glCreateShaderObjectARB, etc.

To access the linking function, import pyglet.gl.lib and use one of link_AGL, link_GLX, link_WGL, link_GL or link_GLU. This is what the generated modules do.

Missing extensions

The latest glext.h on opengl.org and nvidia does not include some recent extensions listed on the registry. These must be hand coded into pyglet.gl.glext_missing. They should be removed when glext.h is updated.

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