Animating layout properties (left/right/top/bottom/margin*) or using
roundProps snaps motion to integer device pixels. Under the seek-by-frame
capture engine this is invisible at high per-frame deltas (fast tweens) but
visibly stutters at low deltas (slow tweens / ease-out tails): sub-pixel
movement rounds to the same pixel for several frames, then jumps a whole
pixel. Transforms (x/y/scale) interpolate sub-pixel and stay smooth.
New rule gsap_non_transform_motion (error):
- Sources timeline tweens from the acorn parser's full animation list, so
label- and relative-positioned tweens (tl.to(..., "label") / "+=1") are
covered and real AST keys avoid phantom-prop / nested-brace misreads.
- Exempts html-in-canvas elements (a <canvas layoutsubtree> ancestor): they
are rasterized from sub-pixel getComputedStyle and do not integer-snap.
Per-element resolution, so a grouped glass+text tween still flags the
plain-DOM half. roundProps is never exempt (it rounds before the style).
- Uses Object.hasOwn for the layout-prop lookup, skips set(), and merges
standalone gsap.* calls.
Migrated 9 registry compositions off layout-prop animation onto transforms,
each render-verified visually identical:
- liquid-glass-{notification,widgets,media-controls,context-menu}: plain-DOM
text overlays -> transforms; glass panels stay on left/top (canvas-exempt).
- vignelli: curtain wipes left:% -> xPercent.
- lt-mask-reveal: sweep left:% -> x px.
- flowchart, flowchart-vertical, decision-tree: cursor paths left/top -> x/y.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
