Live vs. Dead pixels during a raycast.

Keeping track of live (red) and dead pixels (blue to green) during a raycast process. Number of samples per pixel starts out at 1 and goes up to 512. If a pixel doesn't change more than x% over the course of N updates, it is moved to the dead list and no longer evaluated. This drastically speeds up rendering times by only throwing processing cycles at those pixels that actually change. However the current tolerance settings are too loose.

This particular test features a gradient background, two triangles with somewhat transparent colours, four solid black quads and two large quads, one with a blur shader and one with a distortion shader.