Figure 1. Billboard Shadow Generator. Rays are generated from a light source to the edges of a billboard. These rays are projected onto a plane representing the ground. A second billboard with a representative shadow map is rendered at the intersection points on the ground. Press 'h' to show the ray intersection tests. WSAD to move the move the camera. 'r' and 'f' or right mouse drag will change camera elevation. Left mouse drag to point the camera.