motion blur using full screen texture for feedback

Wow, this sure beats my old accumulation-buffer approach to motion blur! Each frame, right before I swap bufffers I draw a quad over the whole scene with very high opacity that contains the result of copying the last frame to a texture. This yields nice exponential decay motion blur (with lovely precision issues at very high settings). Altogether, it seems to run the same speed as without the effect -- I guess thats because I still only draw the scene once per frame.