power vr

[Carter07]

Well done! thanks Henrik
Here some testing (all with ubuffered rendering) sorted by efficacy:

Great increase (perf as not using discard at all):
Lumines: 25 fps -> 60 fps
Tenchu: 35 fps: -> 44 fps (now cpu limited)
Asterix: 36 fps -> 44 fps (now cpu limited)

Modest increase:
Ridge Racer: 17 fps -> 25 fps (was doing 37 with no discard)

No or little change:
Dead to Rights: 17 fps -> 18 fps (was doing 40 with no discard)
Obscure: 21 fps (was doing 34 with no discard)


So it definitevely solved the gpu perf problem on some games, you were right that most games abuse of alpha test.
Hope there is more to do.