I'm working my way thru testing various texdisplace shaders. Wesley already acknowledged a prob with td.twirl in another thread. Perhaps these problems are related. Both td.ripples and td.fisheye render nothing in the bottom-left quadrant. Also td.fisheye seems to require an unusually large signcurvature value to get much effect. Mac Pro, OS1-.6.8, Max 6, Radeon 5870.
Simple test patcher: