70 lines
1.9 KiB
Dart
70 lines
1.9 KiB
Dart
 
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import '../models/ink_point.dart';
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/// Stabilization level for hand-drawn strokes.
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enum StabilizationLevel { none, light, medium, heavy }
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/// Smooths pen input using an Exponential Moving Average (EMA) filter.
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///
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/// - **none**: no smoothing (passthrough)
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/// - **light**: alpha = 0.6 (subtle smoothing)
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/// - **medium**: alpha = 0.4 (moderate smoothing)
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/// - **heavy**: alpha = 0.25 (strong smoothing, removes most tremor)
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///
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/// The formula applied to each coordinate independently:
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/// x_smoothed = alpha * x_raw + (1 - alpha) * x_prev
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class StrokeStabilizer {
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final StabilizationLevel level;
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double? _prevX;
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double? _prevY;
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StrokeStabilizer({this.level = StabilizationLevel.none});
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double get _alpha {
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switch (level) {
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case StabilizationLevel.none:
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return 1.0;
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case StabilizationLevel.light:
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return 0.6;
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case StabilizationLevel.medium:
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return 0.4;
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case StabilizationLevel.heavy:
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return 0.25;
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}
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}
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/// Filters a raw point through the EMA, returning a smoothed point.
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/// Returns the raw point unchanged if level is [StabilizationLevel.none].
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InkPoint filter(InkPoint rawPoint) {
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if (level == StabilizationLevel.none) return rawPoint;
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final alpha = _alpha;
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if (_prevX == null || _prevY == null) {
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_prevX = rawPoint.x;
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_prevY = rawPoint.y;
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return rawPoint;
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}
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final smoothedX = alpha * rawPoint.x + (1 - alpha) * _prevX!;
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final smoothedY = alpha * rawPoint.y + (1 - alpha) * _prevY!;
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_prevX = smoothedX;
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_prevY = smoothedY;
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return InkPoint(
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x: smoothedX,
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y: smoothedY,
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pressure: rawPoint.pressure,
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tilt: rawPoint.tilt,
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timestamp: rawPoint.timestamp,
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pointerDeviceKind: rawPoint.pointerDeviceKind,
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);
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}
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/// Resets the filter state. Call when starting a new stroke.
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void reset() {
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_prevX = null;
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_prevY = null;
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}
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}
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