ported from perforce

RobotAndDonkey.Game/Utils/Hex.cs

@@ -0,0 +1,79 @@
+using System;
+using System.Numerics;
+
+namespace RobotAndDonkey.Game.Utils;
+
+public record struct Hex(int X, int Y)
+{
+    public static int Distance(Hex a, Hex b)
+    {
+        var (acx, acy, acz) = OffsetToCube(a);
+        var (bcx, bcy, bcz) = OffsetToCube(b);
+        return Math.Max(Math.Max(Math.Abs(acx - bcx), Math.Abs(acy - bcy)), Math.Abs(acz - bcz));
+
+        static (int, int, int) OffsetToCube(Hex hex)
+        {
+            var x = hex.X - (hex.Y - (hex.Y & 1)) / 2;
+            var z = hex.Y;
+            var y = -x - z;
+            return (x, y, z);
+        }
+    }
+
+    public static Hex FromWorld(Vector2 coords)
+    {
+        var cx = coords.X * MathF.Sqrt(3) / 3 - coords.Y / 3;
+        var cz = coords.Y * 2 / 3;
+        var cy = -cx - cz;
+        var rx = (int)MathF.Round(cx);
+        var ry = (int)MathF.Round(cy);
+        var rz = (int)MathF.Round(cz);
+
+        var xDiff = MathF.Abs(rx - cx);
+        var yDiff = MathF.Abs(ry - cy);
+        var zDiff = MathF.Abs(rz - cz);
+
+        if (xDiff > yDiff && xDiff > zDiff)
+            rx = -ry - rz;
+        else if (yDiff > zDiff)
+            ry = -rx - rz;
+        else
+            rz = -rx - ry;
+
+        var col = rx + (rz - (rz & 1)) / 2;
+        var row = rz;
+        return new(col, row);
+    }
+
+    public static Hex FromPixel(Vector2 coords, float size)
+    {
+        return FromWorld(new(coords.X / size, coords.Y / size));
+    }
+
+    public Hex GetNeighbour(EDirection direction)
+    {
+        var parity = Y & 1;
+        var dir = offsetDirections[parity, (int)direction];
+        return new(X + dir.X, Y + dir.Y);
+    }
+
+    public Vector2 ToWorld()
+    {
+        var x = MathF.Sqrt(3) * (X + 0.5f * (Y & 1));
+        var y = 3.0f / 2 * Y;
+        return new(x, y);
+    }
+
+    public Vector2 ToPixel(float size)
+    {
+        var w = ToWorld();
+        return new(w.X * size, w.Y * size);
+    }
+
+    public override string ToString()
+    {
+        return $"({X}, {Y})";
+    }
+
+    private static readonly Hex[,] offsetDirections = { { new(+1, 0), new(0, -1), new(-1, -1), new(-1, 0), new(-1, +1), new(0, +1) }, { new(+1, 0), new(+1, -1), new(0, -1), new(-1, 0), new(0, +1), new(+1, +1) } };
+}