nvidia and memexport..

"Arbitrary" was bad wording. I didn't mean arbitrary as in "it can read any frame buffer pixel", but rather that the PS hw can read "it's own" pixel at any point in the PS sw.

Or maybe it's even more restricted than that. Adding a rule like "you can't read a texture after the first access to frame buffer", would help a lot in reducing the number of pixels in flight in the serial part of the work.