I am currently working on a heat haze effect for my engine. I am using Point Sprites as they seems to give better performance, but they have a few drawbacks. Primarily, I can't get any screen space coordinates of each pixel when render (since all input data is simply copied per vertex). I need the screen space coordinates to read the backbuffer and distort it properly. As it is, I calculate the transformed position in the vertex shader, then let it get interpolated per pixel to my pixel shader. With point sprites, since the input is a single vertex, this doesn't work (since there's nothing to interpolate). Short of creating my own quads, does anyone know of any way to handle this?