Interference patterns, of the sort you get when two fine grids overlap slightly out of step: moire.
It comes from folding. Take a coordinate, wrap it so it counts up and then back down again over and over, and you have a value that ramps and reverses with a crease at every turn. Do that, then pick out a shape with a single comparison of the two folded coordinates: the larger of the two draws a plus, the smaller draws a square, the difference draws a diamond.
The reason the output gets so intricate is that each of the three layers folds the layer before it rather than the original picture. You are not stacking three patterns on top of one another, you are folding an already folded thing, and small differences in the scales multiply out into large visible ones. The three results are then added and wrapped, which turns every smooth ramp into hard banding. smoothing softens the point where the wrap jumps, and the blend modes change how the three layers meet.