Make map grid immutable

OpenRA.Game/Map/MapGrid.cs

@@ -10,6 +10,7 @@
 #endregion
 
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.IO;
 using System.Linq;
 using OpenRA.Traits;
@@ -24,8 +25,8 @@ namespace OpenRA
 	public readonly struct CellRamp
 	{
 		public readonly int CenterHeightOffset;
-		public readonly WVec[] Corners;
-		public readonly WVec[][] Polygons;
+		public readonly ImmutableArray<WVec> Corners;
+		public readonly ImmutableArray<ImmutableArray<WVec>> Polygons;
 		public readonly WRot Orientation;
 
 		public CellRamp(MapGridType type, WRot orientation,
@@ -83,10 +84,11 @@ namespace OpenRA
 		{
 			// Enumerate over the polygons, assuming that they are triangles
 			// If the ramp is not split we will take the first three vertices of the corners as a valid triangle
-			WVec[] p = null;
-			var u = 0;
-			var v = 0;
-			for (var i = 0; i < Polygons.Length; i++)
+			int u;
+			int v;
+			ImmutableArray<WVec> p;
+			var i = 0;
+			do
 			{
 				p = Polygons[i];
 				u = ((p[1].Y - p[2].Y) * (dX - p[2].X) - (p[1].X - p[2].X) * (dY - p[2].Y)) / 1024;
@@ -95,7 +97,10 @@ namespace OpenRA
 				// Point is within the triangle if 0 <= u,v <= 1024
 				if (u >= 0 && u <= 1024 && v >= 0 && v <= 1024)
 					break;
+
+				i++;
 			}
+			while (i < Polygons.Length);
 
 			// Calculate w from u,v and interpolate height
 			return (u * p[0].Z + v * p[1].Z + (1024 - u - v) * p[2].Z) / 1024;