Honor each brush's opacity/blend so the brushes feel distinct
(closes TODO(brush-opacity)).
- Shared paint resolver: a stroke's color alpha is multiplied by its
brush opacity; ballpoint/pencil opacity is tied to pressure
(per-stroke average this increment) so a ballpoint reads lighter
than a solid fountain pen.
- Highlighter paints with BlendMode.multiply and draws once, so
cross-stroke overlap darkens like a real marker while self-overlap
doesn't.
- Applied across BOTH render paths (PenCanvas static/live painters and
the PDF _PageOverlayPainter).
Pencil paper-grain texture still deferred (TODO brush-texture); brush
kind is not yet serialized (TODO brush-persist — next). analyze clean,
tests green.
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.
