The experiment uses 3 Canvases. The cnvs is the screen you see. The offScreenCnvs is an off-screen canvas that will store the large circle image. The flipCnvs is an off-screen canvas that has the large circle image copied to it, then the small red circle is drawn on it, and flipped to the visible cnvs.
Comments are made in the InLine script to make it easier to follow.
Please see the E-Prime Command Reference for more information on the Canvas object and E-Basic.
The distance from the cursor and red circle is recorded as it moves around the screen.