https://gitlab.synchro.net/main/sbbs/-/commit/4ba867d0bad38dfe141b8f7e
Modified Files:
src/doors/syncretro/syncretro_quant.c syncretro_quant.h test_quant.c Log Message:
syncretro: take the oldest sixel register, don't rebuild the map

The colour->register map only ever grew, and a frame whose new colours
could not fit threw the whole map away and rebuilt it from that frame.
With shared colour registers -- which is what SyncTERM has, and what
`CSI ? 1070 l` asks every other terminal for -- redefining a register
recolours every pixel already on screen that was drawn with it, so a
rebuild repaints the entire displayed frame in the wrong colours until
the new pixel data lands on top of it.

A console with a small fixed palette never reaches that: Intellivision
has 16 colours, the NES 64. A console whose games fade or cycle their
palette reaches it in seconds. Street Fighter II's attract mode re-tints
every colour of a ~150-colour screen every frame, so the map saturated
and then rebuilt on nearly every frame -- measured over its attract loop,
150 of 256 registers changing meaning in a single frame, and 4.3 per
frame on average.

Give each register the generation that last drew with it and hand a new
colour the least recently used one instead. The frame the terminal is displaying is the youngest generation, so its registers go last, and the colours a frame carries over are stamped before anything is taken -- a
colour still on screen can never lose its register to a colour of the
same frame.

Over the same attract loop that leaves a worst frame of 37 registers
rather than 150, and 0.5 per frame rather than 4.3. Every eviction of a displayed register was checked for a better candidate and none had one:
where it still recolours, prev and current frame genuinely need more than
256 colours between them. Games that never fill the map (tmnt, joust,
pacman, xevious) are byte-for-byte unaffected.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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