A triangle, square, pentagon, or any regular shape up to 64 sides, drawn as a solid figure on a background. Useful on its own, and useful as a mask when you want another effect to apply only inside a shape.
There is no outline and there are no corner points anywhere in the code. Instead every pixel asks a single question: how far am I from the centre, compared with how far the edge is in my direction? To answer it the effect takes the pixel's angle around the centre and folds it into one wedge of the shape, so a hexagon only ever has to solve the problem for one sixth of a turn and the other five come free. Anything closer than the edge is inside, anything further is outside.
One correction stops the shapes changing size as you change sides, so a triangle and a hexagon at the same radius look equally big. smooth controls how crisp the boundary is, from a hard cut to a soft fade.