Yesterday, I read 834144373’s ShaderToy code which did Edge Detection in 97 chars, it was really simple and fast:

However, the result is astonishingly good: Let’s expand the code a little bit:

According to OpenGL manual: fwidth means  abs(dFdx(p)) + abs(dFdy(p)) and fwidthFine is equivalent to abs(dFdxFine(p)) + abs(dFdyFine(p)). One can use a sigmoid function to increase the…