Akiba So eae4493954 fix(zoom): stop re-baseline scale oscillation ...

Device log showed the applied scale oscillating ~1.4x every frame while
the raw pinch was smooth (cur 1.116->0.797->1.074, raw ~0.46). Root cause:
on a pointer-count re-baseline (Windows touch flickers 2<->1<->2 mid-pinch)
the code set _scaleStart = matrix.getMaxScaleOnAxis() — a read-back captured
at a glitchy instant — so the absolute map K = scaleStart/rawScaleAtBaseline
jumped frame to frame.

Fix: anchor the re-baseline to the CLEAN tracked _lastAppliedScale instead
of the live matrix read-back, so the displayed scale is continuous across
the re-baseline regardless of any matrix transient. The math is already
covered by the pinch_scale_solver "same-instant re-baseline" test; this just
feeds it the right value.

flutter analyze: 0. pinch_scale_solver + pen_zoom: pass.

2026-06-23 16:52:14 +08:00

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