Basic Rules
- Playing Field: A flat virtual playing field is used for placing small squares. The standard size is 10 columns wide and 20 rows high, with each unit corresponding to one small square.
- Tetrominoes (Blocks):
A tetromino is a geometric shape composed of 4 small squares. There are 6 types in total, named after the letters S, Z, L, I, O, and T. Their line-clearing capabilities are as follows:
(1) Some games include single-square blocks that can pass through fixed blocks to reach the bottom empty spaces. Other versions may feature additional, special shapes.
Blocks begin to fall slowly from the top of the playing field.
(2) Player Actions:
Players can rotate the blocks in 90-degree increments, move them left or right one square at a time, and accelerate their fall.
(3) When a block reaches the bottom of the field or lands on other blocks and can no longer move, it becomes fixed in place. A new block then appears at the top to start falling.
(4) Clearing Lines:
When a horizontal row in the field is completely filled with blocks, that row is removed, awarding points to the player. Clearing multiple rows at once increases the score multiplier.
(5) Game Over Condition:
The game ends when the fixed blocks stack up to the top of the playing field, preventing any further line clears.
(6) Many versions also display the next block to fall, allowing skilled players to plan their moves. Since endless gameplay is not ideal for commercial purposes, the game’s difficulty typically increases gradually as play continues.
- I: Can clear up to four lines at once.
- L (both left and right versions): Can clear up to three lines, or sometimes two.
- O: Can clear one to two lines.
- S (both left and right versions): Can clear up to two lines, but may easily create gaps.
- Z (both left and right versions): Can clear up to two lines, and similarly may create gaps.
- T: Can clear up to two lines.
- Block Generation and Placement: A pre-set random generator continuously outputs individual blocks at the top of the field. These blocks move, rotate, fall, and are placed according to specific rules, locking into position and filling the field. Each time a block placement completely fills one or more rows, all the squares forming those rows are cleared, awarding points or other rewards. The remaining blocks accumulate, affecting the placement of subsequent blocks.
- Overall Game Over Condition: The game ends if the height of the accumulated, uncleared blocks exceeds the maximum height specified by the playing field (which may not necessarily be 20 rows or the visible area to the player).
While the detailed rules may vary significantly among different versions of the game, the basic rules outlined above remain consistent.