There are two display windows. The graphics content displayed in the upper-left window is a checker like board, the selected geometry (sphere, hollow cylinder or solid cylinder), the shadow cast onto the board by that geometry and a ray drawn from a selected point on the board in the direction of the light. The window content is updated as you make changes to the light direction, the selected point on the board and the selected geometry. The mechanisms for making the changes are available through other windows; there are no user controls attached to this display window.
The second display window, appearing in the lower-left corner, allows you to select a point on the board. The computational results for testing whether the selected point is in the shadow of the object is shown in the technical content window. You select a point on the board with a left mouse click and by dragging the mouse with its left button pressed.