https://gitlab.synchro.net/main/sbbs/-/commit/2d0d5c575e2cc51178be164c
Modified Files:
src/doors/syncdoom/i_video.c render_sixel.c render_sixel.h syncdoom.c Log Message:
syncdoom: make the sixel tier work on SyncTERM

Three fixes that together make SyncTERM render the sixel tier correctly
(it previously garbled and/or scrolled), and let older SyncTERM reach it.

- Stable, define-once palette. The encoder rebuilt a per-frame palette from
the RGB framebuffer and re-emitted all 256 color-register definitions every
frame -- with register numbers assigned in scan order, so the same Doom color
was a different register each frame. That churn corrupted SyncTERM's decoder
(garbled colors every few frames). Now we encode from Doom's native 8-bit
indices (i_video.c exposes the live palette + a change counter) against a
fixed 1:1 register<->index palette, and (re)define the registers ONLY when
Doom actually changes the palette (damage/pickup/radsuit/menu). A steady
scene sends band data alone -- identical palette every frame, ~4KB smaller.

- DECSDM (private mode 80) reset while the sixel tier is active. It defaults
to set, which scrolls the page + appends a newline whenever a full-screen
sixel reaches the bottom -- i.e. every frame. Resetting it pins the sixel at
the page origin and stops the per-frame scroll. Restored on exit/tier-change.

- CTDA sixel auto-detect. SyncTERM advertises sixel only via its private CTerm
Device Attributes (ESC[<c -> capability 4 = pixel ops), not the xterm DA1
flag, so older (no-JXL) SyncTERM used to fall back to text. Probe ESC[<c and
accept cap 4, so those versions auto-select sixel. 1.4+ still prefers JXL
(the tier ladder probes JXL first).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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