read framebuffer to memory slowdown

[aki21]

hmm,i don't really know where it started,and the last revision i tried is 0.9.6 1145,i did'nt update the build and skipped to the latest(1233).also where the old build in buildbot,i can't see them.

as the speed in the game project diva well it like this:
old build:f:gpu=94%
latest build:f:gpu=40-50%
:f:cpu=40-50%

i will try any method possible and report back,also i think we need someone who has the same problem also i guess.