81 lines
2.5 KiB
Dart
81 lines
2.5 KiB
Dart
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// lib/editor/engine/stroke_simplify.dart
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//
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// Ramer–Douglas–Peucker stroke point reduction. A fast Surface-Pen stroke can
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// land hundreds of nearly-collinear samples; thinning them before persistence
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// shrinks the DB row + speeds re-rasterization (R1/R10 perf) with no visible
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// change. Endpoints + perceptually-significant vertices are kept; pressure/tilt
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// ride along on the retained points.
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//
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// Pure geometry over EditorStroke (normalized coords); fully unit-tested. The
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// commit path can call this before saveHost; the live in-progress stroke is left
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// untouched so drawing stays crisp.
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import 'stroke_model.dart';
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/// Returns [stroke] with its points reduced by RDP at [tolerance] (perpendicular
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/// distance in normalized units; larger = more aggressive). Strokes with <= 2
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/// points, or a non-positive tolerance, are returned unchanged.
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EditorStroke simplifyStroke(EditorStroke stroke, {double tolerance = 0.0008}) {
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final pts = stroke.points;
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if (pts.length <= 2 || tolerance <= 0) return stroke;
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final keep = List<bool>.filled(pts.length, false);
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keep[0] = true;
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keep[pts.length - 1] = true;
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_rdp(pts, 0, pts.length - 1, tolerance * tolerance, keep);
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final reduced = <EditorPoint>[
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for (var i = 0; i < pts.length; i++)
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if (keep[i]) pts[i],
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];
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if (reduced.length == pts.length) return stroke;
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return stroke.copyWith(points: reduced);
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}
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// Iterative-friendly recursion over the index range [first, last].
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void _rdp(
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List<EditorPoint> pts,
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int first,
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int last,
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double tolSq,
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List<bool> keep,
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) {
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if (last <= first + 1) return;
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var maxDistSq = 0.0;
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var index = -1;
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final ax = pts[first].x, ay = pts[first].y;
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final bx = pts[last].x, by = pts[last].y;
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for (var i = first + 1; i < last; i++) {
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final d = _perpDistSq(pts[i].x, pts[i].y, ax, ay, bx, by);
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if (d > maxDistSq) {
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maxDistSq = d;
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index = i;
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}
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}
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if (maxDistSq > tolSq && index != -1) {
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keep[index] = true;
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_rdp(pts, first, index, tolSq, keep);
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_rdp(pts, index, last, tolSq, keep);
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}
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}
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/// Squared perpendicular distance of (px,py) from the segment (ax,ay)-(bx,by).
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/// Degenerate segment (a==b) falls back to squared distance to the point.
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double _perpDistSq(
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double px,
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double py,
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double ax,
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double ay,
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double bx,
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double by,
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) {
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final dx = bx - ax, dy = by - ay;
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final lenSq = dx * dx + dy * dy;
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if (lenSq == 0) {
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final ex = px - ax, ey = py - ay;
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return ex * ex + ey * ey;
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}
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final cross = (px - ax) * dy - (py - ay) * dx;
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return (cross * cross) / lenSq;
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}
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