I can set an expression for a color component of a whole frame, for example I can set this expression r=0.5+(sin(frame/10.0)/2) for the Red Component of a Rectangle and the color will oscillate over the course of some 63 frames.
But this sets the color for the whole of the rectangle. I want to be able to set an expression which varies the color components within the same frame, e.g. to set components (1,0,0,1) for the pixel at (1,1) and (0.9, 0.1, 0, 1) for the pixel at (2,1).
How can I achieve this?