BUG: Some problems with effects

[gpvillamil]

I've been going through all the effects in Resolume 3, and a few seem to have bugs.

Circles: does nothing, only black
Distortion: only affects bottome 75% of the screen
Mirror: not clear what is happening - with x and y set to .5, i'm expecting to see a 4 way mirror effect, but lower left corner is missing
Slide: seems to rescale video to 50% horizontal, x and y sliding work as expected