Tactical rotation

bascnab The New Tetris uses smooth falling animation for tetrominoes. The way this implementation mixes the falling animation with collision detection means that when a tetromino must be moved under an overhang to reach a ledge, by the time it has moved left one space with no support it has dropped more than zero spaces. In some cases it can therefore not reach a ledge.

Nothing can be done in the case of the O piece:

There is no problem getting the O piece to here

But if the ledge is further under the overhang we have a problem

The piece can not move left until this point

It cannot move left two spaces before it has dropped more than zero spaces

There are, however, ways of getting a piece other than O further under the overhang by making use of "tactical rotation": rotating the piece in the right direction at the right time.

Examples

Reaching under overhangs

With I pieces

Just holding left from here won't get the I piece in place

Hold left and rotate (either direction) just after this point

As long as the gravity isn't too strong at this point in the game, you'll get to here (or a space above or below)

Rotate the I piece into place

With L and J pieces

This is useful for completing spiral L monosquares on the left and spiral J monosquares on the right (in which case the move is reversed) if the space above the block is already occupied in such a way that the L cannot be overhung as in the second figure of the L/J shuffle below.

Lower the L in this orientation

Start to hold left

Just as the L begins to move left, rotate anticlockwise

The L is moving through the corner piece: keep holding left and soft drop it into place

Finished square

With the opposite multisquares (L on the right or J on the left), the third piece requires some tactical rotation if there is not enough support underneath.

Lower the J piece in this orientation, holding left as soon as possible

The J starts moving left at this point – immediately rotate clockwise

The piece in place

If there is sufficient free space above the construction, an easier method can be used (shown below).

L/J swing

This is useful when building a spiral L monosquare on the right or a spiral J monosquare on the left as above, provided there is enough free space above the construction.

Firm drop to this position

Rotate clockwise twice in quick succession

The piece in place

L/J shuffle

This is useful for completing spiral L monosquares on the left and spiral J monosquares on the right (in which case the move is reversed).

Once the L is clear of the overhang it needs to slide two positions left to lock in place. This can't be done just by holding left

Firm drop the L to hang off the edge

Hold left, rotate clockwise then anticlockwise in quick succession

The L is moving through the corner piece. Keep holding left and soft drop, so it slides left as soon as it can.

Completed square

S/Z pop

This move is required for ZLLZ/SJJS, TTLZ/TTJS and LJZI/JLSI multisquares. All rotations should be reversed for the right-hand versions.

The space marked with must be free. The move is easiest if the space to 's left is also free...

That surely won't fit...

Firm drop to here, then rotate in either direction

Easy

If the space indicated is taken there are two other ways

The easiest is the S/Z wiggle: firm drop to here, then rotate clockwise then anticlockwise in quick succession

The Z piece is sliding down from this position. Firm drop it.

Job done

The second of the two rotations can be performed alone, but this isn't as quick or easy. To do it, rotate anticlockwise just after the Z is in this position...

...before it gets to here

Building a T monosquare quickly

The quickest way to add the final piece of a T monosquare is to spin it into place:

Firm drop the backwards-oriented T piece

Rotate the piece twice quickly

Finished square

If there is no free space above:

With the T piece oriented backwards hold left and soft drop

It catches in the gap. Rotate the piece twice quickly

Finished square