Where Pieces Spawn and Why the Buffer Exists

A couple of hidden rows above the visible field give rotations somewhere to go.

Pieces appear at the top of the well, horizontally centred: the three-wide pieces occupy columns four to six, the O sits in columns five and six, and the I spans four to seven.

The hidden rows

Above the twenty visible rows, TETERI keeps a small buffer of rows you cannot see. They exist for one reason: rotations need somewhere to kick.

When a piece near the ceiling rotates and the kick table offers an upward offset, that offset needs to land somewhere valid. Without buffer rows the rotation would fail, and a piece that is legal everywhere else in the well would become unrotatable at the top, for no reason a player could perceive.

Why the buffer is small

Two rows in this implementation. Larger buffers create their own problem: pieces can end up stacked in space you cannot see, so the board state stops matching what is on screen. Losing to something invisible is worse than an occasional failed rotation.

Two rows is enough for every kick in the standard tables and shallow enough that almost nothing meaningful happens up there.

The consequence for how you stack

Because pieces spawn in the centre, the centre columns are the ones that actually matter for survival. A stack that is high at the edges and low in the middle can survive far longer than one with a central tower, even at identical total height.

That is a genuinely useful bias: when you have a choice of where to put an awkward piece and both options are equally bad for the surface, put it at the edge.

Spawn and the end of the run

The run ends when a spawning piece overlaps something. Because spawn is central, this is almost always a central column filling up, which is why the danger usually announces itself as a spike in the middle rather than an even rise.

TETERI draws its danger line across the whole well, but it is the middle of that line you should be watching.

Versus and the ceiling

Incoming garbage pushes everything up. If the push would force blocks out through the top of the field entirely, that is an immediate loss. The buffer does not save you here: it is two rows, and a garbage hit is frequently four.