ID software actually created the first side scrolling platformer on a computer. Before then, computers had a hard time redrawing the background like the NES did. To solve this problem, John Carmack thought to just redraw the important parts of the background instead of the entire background. "Since the sky is always blue, why redraw it?" To test this out, him and his friends, John Romero and Tom Hall, recreated Super Mario Bros. 3 pixel by pixel, by hand, which they shipped to Nintendo hoping to gain authorization to make an official port. This would latter become the template to the game Commander Keen.