Fix MPos projection

OpenRA.Game/CPos.cs

@@ -78,17 +78,9 @@ namespace OpenRA
 				return new MPos(X, Y);
 
 			// Convert from RectangularIsometric cell (x, y) position to rectangular map position (u, v)
-			//  - The staggered rows make this fiddly (hint: draw a diagram!)
+			// The staggered rows make this fiddly.
-			// (a) Consider the relationships:
-			//  - +1x (even -> odd) adds (0, 1) to (u, v)
-			//  - +1x (odd -> even) adds (1, 1) to (u, v)
-			//  - +1y (even -> odd) adds (-1, 1) to (u, v)
-			//  - +1y (odd -> even) adds (0, 1) to (u, v)
-			// (b) Therefore:
-			//  - ax + by adds (a - b)/2 to u (only even increments count)
-			//  - ax + by adds a + b to v
-			var u = (X - Y) / 2;
 			var v = X + Y;
+			var u = (v - (v & 1)) / 2 - Y;
 			return new MPos(u, v);
 		}
 

OpenRA.Test/OpenRA.Game/CoordinateTest.cs

@@ -10,6 +10,7 @@
 #endregion
 
 using System;
+using System.Linq;
 using NUnit.Framework;
 
 namespace OpenRA.Test
@@ -17,25 +18,74 @@ namespace OpenRA.Test
 	[TestFixture]
 	public class CoordinateTest
 	{
-		[TestCase(TestName = "Test CPos and MPos conversion and back again.")]
+		[TestCase(TestName = "Test CPos to MPos conversion and back again.")]
-		public void CoarseToMapProjection()
+		public void CPosConversionRoundtrip()
 		{
 			foreach (var gridType in Enum.GetValues<MapGridType>())
 			{
-				for (var x = 0; x < 12; x++)
+				var expected = new CellCoordsRegion(new CPos(-12, -12), new CPos(12, 12));
-				{
+				var actual = expected.Select(pos => pos.ToMPos(gridType).ToCPos(gridType)).ToArray();
-					for (var y = 0; y < 12; y++)
-					{
-						var cell = new CPos(x, y);
 
-						// Known problem on isometric mods that shouldn't be visible to players as these are outside the map.
+				Assert.That(expected, Is.EqualTo(actual));
-						if (gridType == MapGridType.RectangularIsometric && y > x)
-							continue;
-
-						Assert.That(cell, Is.EqualTo(cell.ToMPos(gridType).ToCPos(gridType)));
-					}
-				}
 			}
 		}
+
+		[TestCase(TestName = "Test MPos to CPos conversion and back again.")]
+		public void MPosConversionRoundtrip()
+		{
+			foreach (var gridType in Enum.GetValues<MapGridType>())
+			{
+				var expected = new MapCoordsRegion(new MPos(-12, -12), new MPos(12, 12));
+				var actual = expected.Select(pos => pos.ToCPos(gridType).ToMPos(gridType)).ToArray();
+
+				Assert.That(expected, Is.EqualTo(actual));
+			}
+		}
+
+		[TestCase(TestName = "Test directional movement of ToCPos.")]
+		public void TestIsometricCPosConversion()
+		{
+			const MapGridType Isometric = MapGridType.RectangularIsometric;
+			Assert.That(new CPos(0, 0), Is.EqualTo(new MPos(0, 0).ToCPos(Isometric)));
+
+			Assert.That(new CPos(1, 1), Is.EqualTo(new MPos(0, 2).ToCPos(Isometric)));
+			Assert.That(new CPos(2, 2), Is.EqualTo(new MPos(0, 4).ToCPos(Isometric)));
+			Assert.That(new CPos(3, 3), Is.EqualTo(new MPos(0, 6).ToCPos(Isometric)));
+
+			Assert.That(new CPos(1, 0), Is.EqualTo(new MPos(0, 1).ToCPos(Isometric)));
+			Assert.That(new CPos(2, 0), Is.EqualTo(new MPos(1, 2).ToCPos(Isometric)));
+			Assert.That(new CPos(3, 0), Is.EqualTo(new MPos(1, 3).ToCPos(Isometric)));
+
+			Assert.That(new CPos(0, 1), Is.EqualTo(new MPos(-1, 1).ToCPos(Isometric)));
+			Assert.That(new CPos(0, 2), Is.EqualTo(new MPos(-1, 2).ToCPos(Isometric)));
+			Assert.That(new CPos(0, 3), Is.EqualTo(new MPos(-2, 3).ToCPos(Isometric)));
+
+			Assert.That(new CPos(1, -1), Is.EqualTo(new MPos(1, 0).ToCPos(Isometric)));
+			Assert.That(new CPos(2, -2), Is.EqualTo(new MPos(2, 0).ToCPos(Isometric)));
+			Assert.That(new CPos(3, -3), Is.EqualTo(new MPos(3, 0).ToCPos(Isometric)));
+		}
+
+		[TestCase(TestName = "Test directional movement of ToMPos.")]
+		public void TestIsometricMPosConversion()
+		{
+			const MapGridType Isometric = MapGridType.RectangularIsometric;
+			Assert.That(new MPos(0, 0), Is.EqualTo(new CPos(0, 0).ToMPos(Isometric)));
+
+			Assert.That(new MPos(0, 2), Is.EqualTo(new CPos(1, 1).ToMPos(Isometric)));
+			Assert.That(new MPos(0, 4), Is.EqualTo(new CPos(2, 2).ToMPos(Isometric)));
+			Assert.That(new MPos(0, 6), Is.EqualTo(new CPos(3, 3).ToMPos(Isometric)));
+
+			Assert.That(new MPos(0, 1), Is.EqualTo(new CPos(1, 0).ToMPos(Isometric)));
+			Assert.That(new MPos(1, 2), Is.EqualTo(new CPos(2, 0).ToMPos(Isometric)));
+			Assert.That(new MPos(1, 3), Is.EqualTo(new CPos(3, 0).ToMPos(Isometric)));
+
+			Assert.That(new MPos(-1, 1), Is.EqualTo(new CPos(0, 1).ToMPos(Isometric)));
+			Assert.That(new MPos(-1, 2), Is.EqualTo(new CPos(0, 2).ToMPos(Isometric)));
+			Assert.That(new MPos(-2, 3), Is.EqualTo(new CPos(0, 3).ToMPos(Isometric)));
+
+			Assert.That(new MPos(1, 0), Is.EqualTo(new CPos(1, -1).ToMPos(Isometric)));
+			Assert.That(new MPos(2, 0), Is.EqualTo(new CPos(2, -2).ToMPos(Isometric)));
+			Assert.That(new MPos(3, 0), Is.EqualTo(new CPos(3, -3).ToMPos(Isometric)));
+		}
 	}
 }