1. Generate a number of points within the image bounding box.
2. Force some points to be on the bounds.
Modify the current figure form generation system to choose from these points.
3. Generate lines by joining the points.
Modify the figure form generation system to choose from these lines.
4. Subdivide some of the lines.
5. Split some of the overlapping lines.
Alternatively create the hull or polygon for the figure and generate forms within it using points on the border, lines between them, and various subdivisions.
Implement various algorithms for consuming the lines and points. From back to front, most simplifying to most simple:
Voronoi or region growing. (Use a flat coloured plane sometimes.
Don’t use every technique in every drawing. Increase tightness of line following from back to front. Colour by plane.