Epoxy automatically fetches the extension functions on demand, including
the GLX context creation functions. This means that you can't test the
function pointers for NULL anymore, because they're always set to a
resolver function until the first call. Instead, you have to check for the
availability of an extension by the extension's name. Thanks to Isilkor for
catching these.
On windows, epoxy invalidates all extension function pointers when the
GL context changes. This means we need to have an active context at all
times we call an extension function (like wglGetPixelFormatAttribivARB)
or else the code will jump to an invalid pointer. On the other hand, we do
not need to make it reinitialize the pointers ourselves.
Epoxy automatically uses an alias for a function if the requested name is
not available, like glDebugMessageCallbackARB instead of
glDebugMessageCallback. It also does not have the problem with varying
parameter types for that function. So switch to it while removing
GLDEBUGPROCARB_USERPARAM_IS_CONST.
Günther Brammer