One screen ruled across the picture, not one per block

Dithering each block alone is right about the texture and was wrong
about the phase. Every sprite indexed its screen from its own corner, so
whether two identical blocks a cell apart agreed came down to the
screen's period dividing the cell in buffer pixels -- which is
arithmetic luck. At a 32-unit cell that is 96 and every period divides
it, which is why this looked fine on the phone it was reviewed on. At 24
units it is 72: POSTER lands eight pixels out and BILLBOARD twenty-four,
half a period, on any 360-wide screen.

The fix is not a bigger buffer. A ruled screen is a pure function of
position, so passing a window its own offset on the sheet is exactly
equivalent to ruling one screen across the whole picture and cutting
each block out of it -- and the field never has to exist. Diffusion
takes no offset and needs none: its texture is aperiodic, so there is no
phase for it to be out of. The sprite cache gains the phase as a key,
and because a cell is a whole number of periods that is one phase per
class rather than one per square. Cold frames went 6.2ms to 4.4ms at the
coarse end; warm frames are unchanged, because warm frames never built a
sprite.

The whole-number part is now guaranteed rather than hoped for.
fitRuling already stepped a ruling down when a block was too small to
carry it, which is the same kind of rule; it steps down until the period
divides the cell as well. A 32-unit cell keeps the whole ladder and a
24-unit cell stops at COARSE -- the coarse end unavailable there rather
than available and out of register, which is the better failure. A
screen that does not hold register is not a coarser screen, it is a
misprint. Previews pass no grid and are unconstrained: nothing on an
atlas row moves.

And the block is cut at the phase of the square it *rests* on, never the
one it is being dragged through. The ink belongs to the block, so a
piece under a thumb carries its own across the board; a move is one
cell, which is a whole number of periods, so it lands on the pattern it
left with nothing to snap. Taking the phase from the animated position
instead would have made the ink a function of how the piece got there,
which is the same thing as making it depend on whether it was animated
at all.

commit

ff953b0dd805da72b95c137b4052f9cec229c474

parent

a69b1798f115ce5864e0115698381f671b700806

author

Dami <dami.etoile@gmail.com>