Arika Rotation System

Arika Rotation System (also known as ARS) is a set of gameplay mechanics, used in the Tetris: The Grand Master series, Tetris with Cardcaptor Sakura Eternal Heart, and many fan games. It is derived from Sega's rotation system.

Games using Arika Rotation System generally use IRS, fast DAS, lock delay, and sonic drop. Tetrominoes usually appear in the 20th and 19th row, unlike guideline games which appear in the 22nd and 21st rows. The "ARS" and "ARS2" modes of Tetris The Grand Master Ace use a hybrid of TGM rules and Guideline rules.

Tetris with Cardcaptor Sakura Eternal Heart uses a modified version of ARS that does not have Mihara's conspiracy.

Basic rotation

The basic rotation states of pieces is identical to Sega rotation, which was used in older Japanese Tetris games since 1988.

Some defining characteristics include:

• All pieces except for the I-piece have its rotation states aligned towards the bottom of the piece's bounding box. This allows a piece to rotate after landing on a flat surface, without requiring floor kicks.
• I, S, and Z-pieces only have two states, and rotating in either direction simply toggles their state.
• Unlike Sega rotation, L, J, and T pieces can be rotated both clockwise, and counterclockwise.
• The initial state of the L, J, and T tetrominoes have their longest flat side facing up.

Arika Rotation System's basic rotations.

Kicks

When basic rotation fails due to the piece colliding with the edges of the playfield or the stack, two kicks are tested.

The process is as follows:

1. Basic rotation
2. Kick 1 space to the right of basic rotation
3. Kick 1 space to the left of basic rotation

In addition to these rules, there are some extra exceptions where certain kicks are not allowed.

• The I tetromino will never kick.
• L, J, and T-pieces, from their 3-wide orientations, will not kick off their center column.

Center column rule

The center column rule prevents many unusual kicks which would otherwise be possible without the rule. Another side effect of the rule is that some rotations are not reversible, unlike with SRS.

L, J, and T-pieces use a 3x3 bounding box to hold the piece information, when referring to the center column, it means the center column of the bounding box. If any of these three pieces are rotated, an algorithm checks if the piece collides with the stack or playfield edges.

The algorithm for checking colliding blocks searches in the following pattern:

If the first block found in the search is a center column block (cells 2, 5, or 8), the rotation will fail. However, if the first block found isn't in the center column, and a kick is possible, then a kick is applied.

In the situations illustrated below if the block is occupied.

However, there are very similar situations where additional off-center blocks will enable a wall kick. In the situations illustrated below, the upper occupied blocks are off-center and enable the kick even in the presence of occupied blocks in the center column.

Clockwise rotation will successfully kick:

Counter-clockwise rotation will successfully kick:

Kicks added in Tetris The Grand Master 3 Terror-Instinct

I-piece wall kicks

In Terror-Instinct, the I-pieces can kick walls and the stack. There are two different wall kicks.

Try to rotate	Basic rotation fails	Kick 2 space right
Try to rotate	Basic rotation fails	Kick left

Similarly to floor kicks, the I-piece needs to be touching part of the stack to kick one cell to the right.

Try to rotate	Basic rotation fails	No rotation occurs
Try to rotate	Basic rotation fails	Kick right

I tetromino's floor kicks

The I tetromino can kick the floor, but it can be performed only once and cannot kick the floor in mid-air.

Fail

OK

OK

There are 2 different types of floor kicks.

Try to rotate	Basic rotation fails	Kick 1 space up
Try to rotate	Basic rotation fails	Kick 2 space up

T tetromino's floor kicks

The T tetromino can escape from a hollow, up to two times.

Try to rotate

Basic rotation fails

Kick up

Rotating a T or I tetromino after it has floor kicked will permanently set the lock delay for that tetromino to zero. This is actually what prevents the second I floorkick. After the second rotation is processed, movement gets processed, allowing a shift of one cell left or right if it's done fast enough. Gravity is then applied. If the I tetromino is not in contact with an occupied cell below after processing gravity, any attempt to floorkick will fail, as explained above. If contact does exist, the tetromino will instantly lock down, preventing rotation from being processed at all.

The T tetromino has no such restriction, so it IS possible to make it floor kick twice, but it will lock after the second one because there is no way to process rotation again before it locks.

Right side bias

In TGM's rotation system, the Tetrominoes rotate on only one axis resulting in asymmetrical rotations. In this example, the I piece can't rotate on the left side of the stack;

A situation which would work on the right side.

Notice the I has 1 rotation axis;

I piece's rotation axis

This case does not apply to the T tetromino, as it rotates on its center;

T rotation axis

Mihara's conspiracy

Due to the right side bias with wall kicks, doing this move with a J when there is an empty hole right of the block that the J is caught on will lead to a hole.

L works:

Firm drop

Rotate left

Kicks to here

J in the other hand, does not.

Firm drop

Rotate right

Kicks to here

A block (marked as red) is required for the piece to do so.

Firm drop

Rotate right

This fails too

Kicks to here

ACE-ARS and ARS2

Ace's rotation is a hybrid of SRS and ARS. Ace features guideline colors and lock delay is now directly reset by rotation/movement. A maximum of 128 lock delay resets are permitted per piece. Piece spawns that would previously have resulted in death (blocks occupying row 19/20 spawn locations) will now instead cause the piece to spawn higher, to a maximum of rows 21/22. This effectively makes the usable well size 2 rows higher.

ARS2 is available through an Xbox live patch for the game. Normal ARS features Sonic Lock (locking hard drop) and non-locking soft drop. ARS2 reverts these drop mechanics to how it worked in TGM3 and TGM2.

See also

• Sega Rotation
• Tetris Plus 2: The first game to use wall kicks with a Sega-like rotation system.

References

• KAN's detailed explanation of TGM3's new I and T floorkicks