Good points. I should have definitely include perf numbers. This shader https://www.shadertoy.com/view/3l23Rh https://www.shadertoy.com/view/3l23Rh goes from 20

Good points. I should have definitely include perf numbers. This shader https://www.shadertoy.com/view/3l23Rh https://www.shadertoy.com/view/3l23Rh goes from 20-25 fps on my laptop to over 60 when rendering 1/10th of the pixels and up around 57-60 fps when rendering 1/5th of the pixels although I know that's not exactly great benchmarking. I don't think derivatives are a computational problem here (and a few tests seem to confirm it) but the values of the derivatives are definitely ruined in the process.