Add support for polygon selection shapes.

OpenRA.Game/Primitives/Polygon.cs

@@ -0,0 +1,114 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2020 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System;
+using System.Linq;
+
+namespace OpenRA.Primitives
+{
+	public struct Polygon
+	{
+		public static readonly Polygon Empty = new Polygon(Rectangle.Empty);
+
+		public readonly Rectangle BoundingRect;
+		public readonly int2[] Vertices;
+		bool isRectangle;
+
+		public Polygon(Rectangle bounds)
+		{
+			BoundingRect = bounds;
+			Vertices = new[] { bounds.TopLeft, bounds.BottomLeft, bounds.BottomRight, bounds.TopRight };
+			isRectangle = true;
+		}
+
+		public Polygon(int2[] vertices)
+		{
+			if (vertices != null && vertices.Length > 0)
+			{
+				Vertices = vertices;
+				var left = int.MaxValue;
+				var right = int.MinValue;
+				var top = int.MaxValue;
+				var bottom = int.MinValue;
+				foreach (var p in vertices)
+				{
+					left = Math.Min(left, p.X);
+					right = Math.Max(right, p.X);
+					top = Math.Min(top, p.Y);
+					bottom = Math.Max(bottom, p.Y);
+				}
+
+				BoundingRect = Rectangle.FromLTRB(left, top, right, bottom);
+				isRectangle = false;
+			}
+			else
+			{
+				isRectangle = true;
+				BoundingRect = Rectangle.Empty;
+				Vertices = Exts.MakeArray(4, _ => int2.Zero);
+			}
+		}
+
+		public bool IsEmpty { get { return BoundingRect.IsEmpty; } }
+		public bool Contains(int2 xy)
+		{
+			return isRectangle ? BoundingRect.Contains(xy) : Vertices.PolygonContains(xy);
+		}
+
+		public bool IntersectsWith(Rectangle rect)
+		{
+			var intersectsBoundingRect = BoundingRect.Left < rect.Right && BoundingRect.Right > rect.Left && BoundingRect.Top < rect.Bottom && BoundingRect.Bottom > rect.Top;
+			if (isRectangle)
+				return intersectsBoundingRect;
+
+			// Easy case 1: Rect and bounding box don't intersect
+			if (!intersectsBoundingRect)
+				return false;
+
+			// Easy case 2: Rect and bounding box intersect in a cross shape
+			if ((rect.Left <= BoundingRect.Left && rect.Right >= BoundingRect.Right) || (rect.Top <= BoundingRect.Top && rect.Bottom >= BoundingRect.Bottom))
+				return true;
+
+			// Easy case 3: Corner of rect is inside the polygon
+			if (Vertices.PolygonContains(rect.TopLeft) || Vertices.PolygonContains(rect.TopRight) || Vertices.PolygonContains(rect.BottomLeft) || Vertices.PolygonContains(rect.BottomRight))
+				return true;
+
+			// Easy case 4: Polygon vertex is inside rect
+			if (Vertices.Any(p => rect.Contains(p)))
+				return true;
+
+			// Hard case: check intersection of every line segment pair
+			var rectVertices = new[]
+			{
+				rect.TopLeft,
+				rect.BottomLeft,
+				rect.BottomRight,
+				rect.TopRight
+			};
+
+			for (var i = 0; i < Vertices.Length; i++)
+				for (var j = 0; j < 4; j++)
+					if (Exts.LinesIntersect(Vertices[i], Vertices[(i + 1) % Vertices.Length], rectVertices[j], rectVertices[(j + 1) % 4]))
+						return true;
+
+			return false;
+		}
+
+		public override int GetHashCode()
+		{
+			var code = BoundingRect.GetHashCode();
+			foreach (var v in Vertices)
+				code = ((code << 5) + code) ^ v.GetHashCode();
+
+			return code;
+		}
+	}
+}