Best in full screen. 1. Draw 10 lines (either manually or automatically). 2. Keep clicking the arrows until they are all gone. 3. Move the figure around the screen a few times.
Several 3D projects on Scratch use a technique called Binary Space Partitioning (BSP). BSP is a way of working out the right order in which to draw things. If you were drawing a scene that had a fence in it, you could divide the scene up using the fence as the dividing line. Your order of drawing would be: (1) stuff on the far side of the fence; (2) the fence; and (3) stuff on the near side of the fence. BSP basically involves doing that kind of scene-division over and over again. It's all explained in more detail on the Wikipedia page - https://en.wikipedia.org/wiki/Binary_space_partitioning. This is an attempt at an interactive version of the 2D illustrations used on that page (polygons in 3D illustrated by lines in 2D).
