round light filters that bounce around the screen and pass over each other and when they pass over eachother their filters combine. the background is white or some image or the current actual screen. instead of plain circular filters, gems could be used. question: should filters be merely RGB coefficients or should they be spectral envelopes? i think spectral envelopes would not take too much cpu, because it only has to multiply, say, 100 bands only once per unique area of intersection.