Hi,
as I'm going to clean up vsync related stuff on the config-0-0-1-branch I read the code for dynamic glx extension registration in xc/lib/GL/dri/dri_glx.c and xc/lib/GL/glx/glxextensions.[ch]. I stumbled over this comment in front of __glXRegisterExtensions:
** In older versions of libGL (prior to October 2002) we _always_ ** called this function during libGL start-up. Now, we only call ** it from glXGetProcAddress() as a last resort.
However, __glXRegisterExtensions is still called in driCreateDisplay. Hmm, on the other hand I found this comment in radeon_screen.c in front of __driRegisterExtensions:
/* This function is called by libGL.so as soon as libGL.so is loaded. * This is where we'd register new extension functions with the dispatcher.
Do the __driRegisterExtensions functions in the drivers rely on being called during initialisation?
In fact I believe it could be dangerous if __driRegisterExtensions was called later as it may override extensions disabled in e.g. CreateContext due to lacking hardware support. Fortunately __glXRegisterExtensions returns immediately if it is called the second or later time. Maybe it's just a matter of updating a few comments after all.
I'm inclined to believe that the comments in dri_glx.c are just wrong. __glXRegisterExtensions has to be called before a call to glXGetProcAddress. The app can query that string via glXQueryExtensionsString long before calling glXGetProcAddress. In fact, it may never call glXGetProcAddress. I'm sure glxinfo doesn't. :)
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