Add WAngle.ArcTan().

OpenRA.FileFormats/WAngle.cs

@@ -67,6 +67,41 @@ namespace OpenRA
 			return new WAngle(Angle - 512).Tan();
 		}
 
+		public static WAngle ArcTan(int y, int x)
+		{
+			if (y == 0)
+				return new WAngle(x >= 0 ? 0 : 512);
+
+			if (x == 0)
+				return new WAngle(Math.Sign(y)*256);
+
+			var ay = Math.Abs(y);
+			var ax = Math.Abs(x);
+
+			// Find the closest angle that satisfies y = x*tan(theta)
+			var bestVal = int.MaxValue;
+			var bestAngle = 0;
+			for (var i = 0; i < 256; i++)
+			{
+				var val = Math.Abs(1024*ay - ax*TanTable[i]);
+				if (val < bestVal)
+				{
+					bestVal = val;
+					bestAngle = i;
+				}
+			}
+
+			// Calculate quadrant
+			if (x < 0 && y > 0)
+				bestAngle = 512 - bestAngle;
+			else if (x < 0 && y < 0)
+				bestAngle = 512 + bestAngle;
+			else if (x > 0 && y < 0)
+				bestAngle = 1024 - bestAngle;
+
+			return new WAngle(bestAngle);
+		}
+
 		// Must not be used outside rendering code
 		public float RendererRadians() { return (float)(Angle * Math.PI / 512f); }
 		public float RendererDegrees() { return Angle * 0.3515625f; }