Making a new GLX context is pretty slow on most of the mesa-based drivers I've used, even g3d. I think that's what makes Qt4's OpenGL renderer so unbearably slow: there's not really any way to get around the fact that each menu popup and tooltip has to be a window, and each window gets its own context.
Not to say this patch could help Qt4, of course... just that I've seen context creation overhead first-hand. Anything we can do to create fewer contexts is a big win.


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