- New frame-by-frame export pipeline in src/lib/frameExport.ts: loads
scene images, walks rangeIn..rangeOut at scene.fps, drawSceneFrame
to an offscreen canvas, awaits a per-frame callback, yields every
4 frames to keep progress responsive, honours AbortSignal.
- Animated GIF via gifenc (per-frame quantize/palette, ~5 KB lib).
- Animated PNG via UPNG.js + pako (lossless RGBA, alpha-aware, ~30 KB).
- drawSceneFrame now clearRects first and skips the background fill
when scene.canvas.background === 'transparent' — prerequisite for
the alpha to reach the APNG output.
- DocumentDrawer: new checkerboard toggle next to the colour picker
flips the stage between its last-picked colour and transparent;
disabled swatch + 'Transparent' hex label make the state obvious.
- ExportDialog: three new option rows — Animated GIF, Animated PNG,
and an APNG preview page that bundles the rendered APNG into a
standalone HTML with a checkerboard backdrop + dark/light toggles
for verifying transparency at a glance.
- Tests: renderFrames frame count + abort, GIF header magic, APNG
acTL presence, transparent round-trip (decoded alpha == 0 on
un-painted pixels), preview HTML structure, and the two UI tests
covering ExportDialog's new rows and the progress-view transition.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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