Add polygon shape

StructureHelperCommon/Models/Shapes/Logics/PolygonGeometryUtils.cs

@@ -0,0 +1,73 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows.Shapes;
+
+namespace StructureHelperCommon.Models.Shapes
+{
+    public static class PolygonGeometryUtils
+    {
+        public static bool DoPolygonsEdgesIntersect(IPolygonShape polygon)
+        {
+            var vertices = polygon.Vertices;
+            int n = vertices.Count;
+
+            if (n < 4)
+                return false; // Triangles cannot self-intersect
+
+            for (int i = 0; i < n; i++)
+            {
+                var a1 = vertices[i].Point;
+                var a2 = vertices[(i + 1) % n].Point;
+
+                for (int j = i + 1; j < n; j++)
+                {
+                    var b1 = vertices[j].Point;
+                    var b2 = vertices[(j + 1) % n].Point;
+
+                    // Skip adjacent edges (they share a vertex)
+                    if (AreAdjacent(i, j, n, polygon.IsClosed))
+                        continue;
+
+                    if (SegmentsIntersect(a1, a2, b1, b2))
+                        return true;
+                }
+            }
+
+            return false;
+        }
+
+        private static bool AreAdjacent(int i, int j, int n, bool isClosed)
+        {
+            // Edges (i,i+1) and (j,j+1) are adjacent if:
+            if (j == i) return true;
+            if (j == i + 1) return true;
+            if (i == j + 1) return true;
+
+            // Special case: first and last edges in closed polygon
+            if (isClosed &&
+                ((i == 0 && j == n - 1) || (j == 0 && i == n - 1)))
+                return true;
+
+            return false;
+        }
+
+        private static bool SegmentsIntersect(IPoint2D p1, IPoint2D p2, IPoint2D q1, IPoint2D q2)
+        {
+            return (Orientation(p1, p2, q1) * Orientation(p1, p2, q2) < 0) &&
+                   (Orientation(q1, q2, p1) * Orientation(q1, q2, p2) < 0);
+        }
+
+        private static int Orientation(IPoint2D a, IPoint2D b, IPoint2D c)
+        {
+            double val = (b.Y - a.Y) * (c.X - b.X) -
+                         (b.X - a.X) * (c.Y - b.Y);
+
+            if (Math.Abs(val) < 1e-12) return 0;  // Collinear
+            return (val > 0) ? 1 : -1;            // Clockwise / Counter-clockwise
+        }
+    }
+
+}