Four to six square beams are joined into a ring. Seen along the (1,1,1) direction, a gap between the end of the ring and its start counts for nothing on screen as long as that gap runs along (1,1,1) itself. A ring that never closes in space therefore reads as a closed polygon. Only six directions are available in this view, so six sides is as far as a convex ring goes; three sides is the Penrose triangle itself, which has a page of its own.
The panel names at the top right open the polygon, motion, and color panels. Polygon sets the number of sides, the length of the shorter sides, the gap that closes the ring, the thickness of the beams, how far the figure is turned, and how much of the screen it fills. Each longer side is its paired shorter side plus the gap, so a small gap gives an even polygon and a short side pulls the ring back toward a triangle. Motion sets the travelling blocks, the speed, and whether it runs. Color sets the top face, the right face, the left face, the outline, the blocks, and the ground.
Drag the stage to move the figure and use the wheel to zoom; the field at the bottom right takes a zoom value too. Double-click a panel title to switch how the panels are laid out. In the movable layout you drag panels wherever you like and keep several open at once; in the fixed layout a single panel sits in the top right.