61 lines
1.6 KiB
C#
61 lines
1.6 KiB
C#
using System.Collections.Generic;
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using System.Linq;
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namespace OpenNest.Geometry
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{
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public static class ConvexHull
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{
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public static Polygon Compute(IList<Vector> points)
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{
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if (points.Count < 3)
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{
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var result = new Polygon();
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result.Vertices.AddRange(points);
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return result;
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}
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var sorted = points.OrderBy(p => p.X).ThenBy(p => p.Y).ToList();
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var lower = new List<Vector>();
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foreach (var p in sorted)
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{
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while (lower.Count >= 2 && Cross(lower[lower.Count - 2], lower[lower.Count - 1], p) <= 0)
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lower.RemoveAt(lower.Count - 1);
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lower.Add(p);
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}
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var upper = new List<Vector>();
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for (int i = sorted.Count - 1; i >= 0; i--)
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{
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var p = sorted[i];
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while (upper.Count >= 2 && Cross(upper[upper.Count - 2], upper[upper.Count - 1], p) <= 0)
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upper.RemoveAt(upper.Count - 1);
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upper.Add(p);
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}
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// Remove last point of each half because it's repeated
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lower.RemoveAt(lower.Count - 1);
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upper.RemoveAt(upper.Count - 1);
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lower.AddRange(upper);
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var hull = new Polygon();
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hull.Vertices.AddRange(lower);
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hull.Close();
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hull.UpdateBounds();
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return hull;
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}
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private static double Cross(Vector o, Vector a, Vector b)
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{
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return (a.X - o.X) * (b.Y - o.Y) - (a.Y - o.Y) * (b.X - o.X);
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}
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}
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}
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