Have you ever looked really carefully at the background at it races past while you carefully guide Topsy to catch each new coin? This background is actually composed of five layers. Each layer is cloned horizontally to create the illusion of an infinite strip. In order for this to work seemlessly, the left and right edges of each layer must match exactly. In addition, as Topsy races after the coins, each layer is translated horizontally at different speeds. The closest layers move faster. This creates the illusion of depth. The background appears almost three dimensional.
The five layers are shown below. The image of each layer is shown twice so you can see how the two edges almost perfectly allign in the middle. I've left a small one or two pixel gap, so you can readily see where the two tiles meet. This gap cannot be seen in the game.
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