34 lines
1.2 KiB
Dart
34 lines
1.2 KiB
Dart
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// lib/editor/engine/pen_physics.dart
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//
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// Simple physical tip model: modulate stroke width by tip velocity so fountain
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// ink feels slightly thinner when moving fast (starvation), while ballpoint
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// stays nearly velocity-invariant.
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//
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// TODO(pen-physics-wire): wired at capture in PenCanvas._toNormalized via
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// tip velocity × pressure. PDF editor path still uses brush gamma only.
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import 'brush.dart';
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/// Modulate width fraction by tip velocity (page-normalized units per second).
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///
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/// Fountain: faster → slightly thinner (ink starvation feel).
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/// Ballpoint: nearly ignore velocity.
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/// Pencil: mild thinning at speed.
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/// Highlighter: ignore velocity (flat marker).
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double tipVelocityWidthScale(BrushKind kind, double speedNormPerSec) {
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final speed =
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speedNormPerSec.isNaN || speedNormPerSec < 0 ? 0.0 : speedNormPerSec;
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// Reference: ~2 page-widths/sec ≈ fast handwriting; clamp influence to [0,1].
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final t = (speed / 2.0).clamp(0.0, 1.0);
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switch (kind) {
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case BrushKind.fountainPen:
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return 1.0 - 0.15 * t;
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case BrushKind.ballpoint:
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return 1.0 - 0.02 * t;
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case BrushKind.pencil:
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return 1.0 - 0.08 * t;
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case BrushKind.highlighter:
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return 1.0;
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}
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}
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