Adaptive tile refresh

Adaptive tile refresh is a computer graphics technique for sidescrolling games, famously used by id Software's John Carmack to compensate for the poor graphics performance of PCs in the early 1990s. Its principal innovation was a novel use of several EGA hardware features to perform the scrolling in hardware. The technique is named for its other aspect, the tracking of moved graphical elements in order to minimize the amount of redrawing required in every frame. Together, the combination saves the processing time that would have been required for redrawing the entire screen.

Because CGA (the previous generation of PC graphics hardware) lacked features for scrolling in hardware, scrolling would previously have had to be done in software, by redrawing the entire screen for every frame – a task for which PCs of the time lacked the performance to carry out. Adaptive tile refresh minimized the computing power required for sidescrolling games to within the reach of available hardware, and thus made such games possible on the PC for the first time.

The technique was eventually used to create the PC sidescroller, Commander Keen.

Adaptive tile refresh using hardware scrolling made its first appearance in an unreleased test game dubbed "Dangerous Dave in Copyright Infringement". Dangerous Dave was a title previously used by John Romero while programming games for Softdisk. The new game was a recreation of the first level of Nintendo's Super Mario Bros. 3, intended as a realistic test bed for the adaptive tile refresh concept, and was developed within a week. The team of future id Software employees, still working for Softdisk, then recreated the entire Mario game, hoping that Nintendo would license the game for PC. Nintendo declined the offer to release the game after id Software finished it.

The first market appearance of Carmack's adaptive tile refresh came in id Software's first installment of the Commander Keen game series, Marooned on Mars. Commander Keen was an immediate shareware success, due to its groundbreaking features and gameplay.

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