add extension method: Vector2.Rotate()

GitOrigin-RevId: ee1e84ff18

Shared/Geometry.cs

@@ -5,6 +5,16 @@ using System;
 
 namespace SemiColinGames {
 
+  public static class Geometry {
+    public static Vector2 Rotate(this Vector2 point, float angle) {
+      float cos = FMath.Cos(angle);
+      float sin = FMath.Sin(angle);
+      return new Vector2(
+        point.X * cos - point.Y * sin,
+        point.Y * cos + point.X * sin);
+    }
+  }
+
   // Math functions that return floats rather than doubles, for convenience.
   public static class FMath {
     public const float PI = (float) Math.PI;