A tetromino's spawn location is the place where it enters the playfield. The specific locations vary across different rotation systems, although they share the common characteristic of being between rows 20-24 and columns 4-7. Tetris guideline games in particular have two invisible rows above row 20 where the active tetromino spawns.
Left-handed vs. right-handed
L, J, T, S and Z pieces rotate in a 3x3 box and spawn horizontally in most games. There's no unambiguous way to spawn a 3 columns-wide piece in a 10 columns-wide matrix because it will always be off-center. The game designers must decide between these 2 choices:
- left-handed: 3 empty columns on left side, 4 empty columns on right side
- right-handed: 4 empty columns on left side, 3 empty columns on right side
The very first Tetris games (Electronika, IBM PC or the versions by Mirrorsoft) used right-handed. Nowadays, left-handed is the standard (e.g. see SRS). Some Tetris games used left-handed and right-handed simultaneously (e.g. Microsoft Entertainment Pack). There are cases where companies went for left-handed and right-handed in different games:
On the other hand, I and O pieces can be centered in a 10 columns-wide matrix. Still, they are not centered in every game. For example, in Tetris (PC, Spectrum HoloByte) the O piece spawns one column more to the left, or in Tetris (Sinclair Spectrum) the I piece spawns one column more to the right.
Spawn locations in more recent guideline games
In the more recent guideline games such as Tetris Friends, the game first tries to spawn tetrominos in rows 20-21. If it fails then the game tries rows 21-22 like in older guideline games. If both attempts fail then the game ends.
For example, in this playfield all pieces except I spawn in rows 20-21 (shown in the outline), but I spawns in rows 21-22 (outside of the screen):
Tetris at tetris.com spawns the pieces inside of the playfield (rows 19-20) just like the Tetris The Grand Master series (including Classic Rule in TGM3) and older games, but tries to push the piece up to twice if the piece would overlap with the existing blocks on the field. I Tetrominos spawn at the 19th row, unlike other Tetris games.
