reference / pictures
mask
A new picture that shows only where a stencil picture is white and solid: mask photo by shape. The stencil is stretched over the picture.
photo = load "landscape.png"stencil = canvas 200 200draw into stencil [ background black no stroke fill white circle at 100 100 radius 80]background 40image (mask photo by stencil) at 100 50 width 200
How to write it
mask picture by picture
Gives a picture.