The twelve tiling patterns from pattern(), used as a stencil between two pictures instead of being drawn as a picture in their own right. Checkerboard, dots, hexagons, stripes, rings, spirals, triangles, hearts, waves and zigzags all work.
Each pattern produces a value from black to white at every point, and that value chooses which picture shows through.
The same smoothness control that softens the edges of a drawn pattern here softens the handover between the two pictures. At zero they meet along a hard geometric line. Turned up, they cross-fade through the pattern's edges, which turns a checkerboard into something closer to a soft dappling.
Rotation and scale act on the stencil before it is used, so you can retune the pattern without touching either source.