Star
Example Links
Based on work by Inigo Quilez
https://iquilezles.org/articles/distfunctions2d/
https://www.shadertoy.com/view/3tSGDy
Calculate the distance of the point p from the star with radius r, and a relative value rf controlling the depth of the stars points.
The calculation assumes we're centered on the origin.
Inside the square is a negative value, so we flip it, and use step to get a hard edge.
Output as a grey scale.