Mode 7
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The term Mode 7 originated on the Super NES video game console, on which it describes a simple texture mapping graphics mode that allows a background layer to be rotated and scaled. By modifying the scaling and positioning of the layer on a scanline-by-scanline basis a simple perspective effect can be applied, transforming the layer into a 2D horizontal texture-mapped plane that trades height for depth.
Mode 7-style rendering is generally used on systems with strong 2D capabilities but no dedicated 3D support. Classic Mode 7 games include the Super NES titles Secret of Mana, F-Zero and Super Mario Kart. The effect was later revisited in Game Boy Advance incarnations of F-Zero, Super Mario Kart and Driver.
The Super NES console has eight modes, numbered from 0 to 7, for displaying background layers, the last one having a single background layer that can be scaled and rotated. The Game Boy Advance version has scaling and rotation for traditional tiled backgrounds in its modes 1 and 2 and scaling and rotation for bitmaps in modes 3 through 5 (used less often because of technical limitations). On each machine supporting this effect, it is possible to change the scaling/rotation values during the horizontal blanking period of each scanline in order to draw a flat plane in a perspective projection; this became thought of as the characteristic "Mode 7" effect. More complex effects such as fuzz are possible by using other equations for the position, scaling, and rotation of each line. This graphical method was not only suited to racing games, it was also (and still is on GBA) used extensively for the overworld sections of roleplaying games such as Square Co., Ltd.'s popular 1994 hit Final Fantasy VI. The effect enabled developers to create the impression of sprawling worlds that continued forever in the distance. Mode 7 was also heavily used in other Square Co., Ltd. RPGs for magical spells.
On the Super NES, a variation of Mode 7 allows pixels of the background layer to be in front of sprites. Examples are Contra III: The Alien Wars (stage 2) and Tiny Toon Adventures (intro screen). The GBA can make the same effect by using mode 2, which provides two "Mode 7" layers, and putting the sprites between the layers.
Many PC games, most notably Wacky Wheels, have a Mode 7 effect made by a completely software-based method. In addition, there is a Mode 7 extension for the software authoring program Multimedia Fusion which allows creators to make semi-3D games.
During the days of the Super NES, Mode 7 was one of Nintendo's favorite selling points (Nintendo Power, SNES Player's Guide). For example, when the game Teenage Mutant Ninja Turtles: Turtles in Time was ported from the arcade to the SNES, a level was changed from side-scrolling to Mode 7.
The Sega Mega Drive/Sega Genesis did not have a comparable hardware-native feature to Mode 7, although the Sega CD add-on did add such a feature; it was used prominently in the Special Stages of Sonic CD, for example. However, some comparable technical feats could be programmed straight into a game by the developers, resulting in similar effects seen in games such as Castlevania: Bloodlines or Contra: Hard Corps.
[edit] Hardware
The PPUs (picture-processing units) of the SNES use two 8-bit 64-KByte RAM chips. One PPU can access the tile map (128 x 128 tiles) and the other PPU can access the tile set (256 tiles, 8x8 pixels in 256 colors) in a single cycle. (See anomie's romhacking.net/docs/regs.txt for more information.)
