Replace the 2-tool ink system with a data-driven, Krita-style
BrushProfile (lib/editor/engine/brush.dart). Adding a brush is a
const map entry, not render-path branching.
Four presets from the rnote/krita spec:
- fountain pen: quadratic (p^2) pressure, wide dynamic width
- ballpoint: near-constant width (thinning 0.15)
- highlighter: flat width, square caps
- pencil: sqrt(p) pressure, moderate width
Pressure is pre-warped per brush via PressureCurve(gamma) before
perfect_freehand; geometry fields (thinning/streamline/smoothing/
caps) flow through the shared stroke recipe so the PDF overlay and
the note/slide PenCanvas both honor the brush. Brush kind is now
persisted on the stroke model. Picker added to all three toolbars.
Opacity/multiply and pencil grain are carried as data but not yet
composited (TODO brush-opacity / brush-texture); this increment is
width + pressure-curve differentiation. analyze clean, 283 tests.
pdf_service._buildFreehandPdfPath hardcoded its OWN StrokeOptions
(thinning:0.7, streamline:0.5) instead of the shared geometry — the R7
hairline-export divergence. The prior pen-feel commit (streamline 0.5→0.32 on
screen) widened the gap: export still rendered at 0.5.
Extract the ONE perfect_freehand recipe into stroke_geometry.freehandOutlinePoints
(owns thinning/smoothing/streamline/simulatePressure). buildStrokeOutline (screen)
and pdf_service (export, via InkStroke→pfPoints) now both call it, so the
StrokeOptions live in exactly one place and screen↔export can't drift again.
Export now matches screen: thinning 0.85 (kDefaultPenThinning), streamline 0.32.
test/export_geometry_test.dart pins it: buildStrokeOutline traces exactly the
shared outline; default thinning == kDefaultPenThinning; thinning is wired;
empty input is safe.
flutter analyze lib/editor clean; 78/78 tests pass (+4).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
