Super Rotation System, or SRS is the current Tetris Guideline standard for how tetrominoes behave, in a broad sense. SRS represents where and how tetrominoes spawn, how they rotate, and what wall kicks they may perform. In TI, a player may choose between World and Classic rotation styles. World closely resembles SRS, and Classic closely resembles the rotation styles of its predecessors TGM and TAP. Henk Rogers, in his effort to unify all new Tetris games into the Tetris Guideline, required Arika to include SRS, which is called World in Ti. SRS traces its routes back to 1991 when BPS introduced its signature third and fourth orientations for the S, Z, and I tetrominoes in their Tetris 2+Bombliss. Later would come flipped-side-up spawned T, L, and J tetrominoes and flexible new wall kicks. Probably the most accurate SRS finds itself in BPS's latest games Tetris Worlds and Tetris Deluxe, which both feature exact same rotation styles.
The basic rotation states are shown in the diagram on the right.
Some points to note:
When unobstructed, the tetrominoes all rotate purely about a single point. These apparent rotation centers are shown as circles in the diagram.
It is a pure rotation in a mathematical sense, as opposed to the combination of rotation and translation found in other systems such as Sega Rotation and Atari Rotation.
As a direct consequence, the J, L, S, T and Z tetrominoes have 1 of their 4 states (the spawn state) in a "floating" position where they are not in contact with the bottom of their bounding box.
This allows the bounding box to descend below the surface of the stack (or the floor of the playing field) making it impossible for the tetrominoes to be rotated without the aid of floor kicks.
The S, Z and I tetrominoes have two horizontally oriented states and two vertically oriented states.
For the "I" and "O" tetrominoes, the apparent rotation center is at the intersection of gridlines, whereas for the "J", "L", "S", "T" and "Z" tetrominoes, the rotation center coincides with the center of one of the four constituent minoes.
When the player attempts to rotate a tetromino, but the position it would normally occupy after basic rotation is obstructed, (either by the wall or floor of the playfield, or by the stack), the game will attempt to "kick" the tetromino into an alternative position nearby.
Some points to note:
When a rotation is attempted, 5 positions are sequentially tested (inclusive of basic rotation); if none are available, the rotation fails completely.
Which positions are tested is determined by the initial rotation state, and the desired final rotation state. Because it is possible to rotate both clockwise and counter-clockwise, for each of the 4 initial states there are 2 final states. Therefore there are a total of 8 possible rotations for each tetromino and 8 sets of wall kick data need to be described.
The positions are commonly described as a sequence of ( x, y) kick values representing translations relative to basic rotation; a convention of positive x rightwards, positive y upwards is used, e.g. (-1, 2) would indicate a kick of 1 cell left and 2 cells up.
The J, L, S, T and Z tetrominoes all share the same kick values, the I tetromino has its own set of kick values, and the O tetromino does not kick.
Several different conventions are commonly used for the naming of the rotation states. On this page, the following convention will be used:
0 = spawn state
1 = state resulting from a clockwise rotation ("right") from spawn
2 = state resulting from 2 successive rotations in either direction from spawn.
3 = state resulting from a counter-clockwise ("left") rotation from spawn
Since Henk Rogers has not been directly involved with a game boasting 20G aside from Tetris Zone, and the guideline Marathon mode only reaches 2.36G (same as Tetris Worlds), certain behaviors are undefined in the Tetris Guideline. Tetris Worlds reaches only 2.36G. Minna no Soft Series: Tetris Advance was the first game to feature SRS and 20G. TGM3 and TGM ACE are the second and third, and Tetris DS (TDS) is the fourth. Though the rotations are identical, these games have different mobility restrictions due to their different order of processing events in between frames.
In this example, Left is being held and then a clockwise rotation is initiated.
The above example ends mid-frame. So the figure on the right is never actually rendered. It simply represents the internal game status after rotation has been processed.
Now, if the game processes movement followed by gravity, the following scenario will happen (as found in TGM3, TGMA and Tetris Zone). This is most likely the result of the relatively fast DAS.
On the other hand, if gravity is processed next, the following scenario will happen (as found in TDS). This could be the result of either movement processed after gravity, movement processed before rotation, or (most likely in the case of TDS) movement occurring one or more frames after both rotation and gravity due to slow DAS.