Drag train. See perspective change. Spacebar switches train to square.
Connects squares' corners to vanishing point. Shows one-point perspective, as in drawing. Each corner and the train image follow mouse position. Squares always in plane of screen. To emphasize that, I use solid shapes which do not bend, as in 1 point perspectivism (in this case. That's a limitation of 1-point perspective. To overcome that limitation requires 2-point (or 3-point) perspective. But this over-simplification of 1-point perspectivism is also leads to simple rules and simple code. Added train for effect.
