Zoom flicker root cause (from the on-device badnote_input_log.txt): the pinch
computed its per-frame scale change as desiredScale / getMaxScaleOnAxis(), i.e.
it fed the LIVE matrix back into its own update. Consecutive frames in the log
show `cur` (the live read) dropping to 0.75-0.89 for a single frame while the
result track stayed smooth, so the code demanded a 1.3-1.4x correction that
popped the zoom bigger/smaller and snapped back. The >1.4 glitch guard missed it
because the spikes sat at 1.31-1.40.
Fix: the scale branch of PenInteractiveViewer now drives the transform
ABSOLUTELY from a gesture-start snapshot (_scaleStart, _referenceFocalPoint) plus
the recognizer's clean, monotonic cumulative details.scale. Each frame is fully
re-derived in closed form (pure scale+translate, no matrix inversion, no live
read-back), so a transient mis-read or interleaved write cannot survive into the
next frame. The per-frame glitch guard now keys on the recognizer's own
scale-ratio (the true finger motion) instead of the corrupted live read. 2-finger
pan still falls out of the same focal-anchor formula.
Pen feel: lower perfect_freehand streamline 0.5 -> 0.32 (new shared constants
kPenStreamline/kPenSmoothing, single-sourced across screen + export so the
parity test still holds). At 0.5 a quick flick lagged so far behind the pen that
short fast strokes collapsed toward their start and rendered as a dot
("写字识别成单击"); 0.32 tracks the real path for a crisper, lower-latency feel.
flutter analyze lib/editor clean; 66/66 tests pass (incl. screen==export parity).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
W1 — Custom pen width + pressure sensitivity (Saber-style):
- Root cause of "压感没用": perfect_freehand 1.0.4 IGNORES real stylus pressure
(hardcodes radius=size/2 when simulatePressure=false) — width never tracked pen
force. Upgraded perfect_freehand ^1.0.0 -> ^2.0.0 (honors real pressure); migrated
all 5 getStroke call sites to the 2.x API (PointVector / StrokeOptions / Offset).
- De-hardcoded `thinning` into `kDefaultPenThinning` (0.85), single source shared by
the on-screen painter and the PDF export path; exposed as PenConfig.pressureSensitivity
with a Pressure Sensitivity slider; live-applies via a config listener.
W3 — Native Windows pen plugin (tilt + barrel/eraser buttons):
- windows/runner/pen_channel.{h,cpp}: observe WM_POINTER at the TOP of MessageHandler
(before HandleTopLevelWindowProc, which Flutter uses to consume pen events), read
GetPointerPenInfo penFlags + tilt, stream over EventChannel('badnote/pen'); non-consuming.
- PenInputService: single latched hardware state (no Win32-pointerId<->event.pointer
correlation); graceful no-op off-Windows.
- pen_canvas maps barrel/inverted/eraser through PenConfig.sideButton/eraserEnd
(eraser/undo/toggleTool/pan) and captures tilt into PenPoint.tilt -> EditorPoint.tilt.
W2 — Zoom flicker: page raster isolated in its own RepaintBoundary (safe interim);
definitive crisp-on-zoom fix gated on the on-device root-cause probe (plan M3).
Plans: ralplan-consensus plan at docs/plans/2026-06-22-badnote-pen-polish.md
(Architect APPROVE-WITH-MUST-FIX M1-M4 + Critic ITERATE->APPROVE).
Tests: 58/58 pass incl. shared-thinning invariant + thinning-affects-outline +
tilt-adapter round-trip. flutter analyze clean; linux debug build OK.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
