Implement missing origin calculations.

Dashboard.Common/Box2d.cs

@@ -25,19 +25,43 @@ namespace Dashboard
         {
         }
 
-        public static Box2d FromPositionAndSize(Vector2 position, Vector2 size, Origin anchor = Origin.Center)
+        public static Box2d FromPositionAndSize(Vector2 position, Vector2 size, Origin anchor = Origin.Center) =>
+            // Hoping the redundent additions+muls become conditional fma instructions.
+            anchor switch
             {
-            Vector2 half = size * 0.5f;
+                Origin.Left => new Box2d(
-            switch (anchor)
+                                        position + (size * new Vector2(0.0f, -0.5f)),
-            {
+                                        position + (size * new Vector2(1.0f, 0.5f))
-                case Origin.Center:
+                                    ),
-                    return new Box2d(position - half, position + half);
+                Origin.TopLeft => new Box2d(position, position + size),
-                case Origin.TopLeft:
+                Origin.Top => new Box2d(
-                    return new Box2d(position, position + size);
+                                        position + (size * new Vector2(-0.5f, 0f)),
-                default:
+                                        position + (size * new Vector2(0.5f, 1f))),
-                    throw new NotImplementedException();
+                Origin.TopRight => new Box2d(
-            }
+                                        position + (size * new Vector2(-1.0f, 0.0f)),
-        }
+                                        position + (size * new Vector2(0.0f, 1.0f))
+                                    ),
+                Origin.Right => new Box2d(
+                                        position + (size * new Vector2(-1.0f, -0.5f)),
+                                        position + (size * new Vector2(0.0f, 0.5f))
+                                    ),
+                Origin.BottomRight => new Box2d(
+                                        position + (size * new Vector2(-1.0f, -1.0f)),
+                                        position + (size * new Vector2(0.0f, 0.0f))
+                                    ),
+                Origin.Bottom => new Box2d(
+                                        position + (size * new Vector2(-0.5f, -1.0f)),
+                                        position + (size * new Vector2(0.5f, 0.0f))
+                                    ),
+                Origin.BottomLeft => new Box2d(
+                                        position + (size * new Vector2(0.0f, -1.0f)),
+                                        position + (size * new Vector2(1.0f, 0.0f))
+                                    ),
+                Origin.Center => new Box2d(
+                                        position + (size * new Vector2(-0.5f, -0.5f)),
+                                        position + (size * new Vector2(0.5f, 0.5f))),
+                _ => throw new ArgumentOutOfRangeException(nameof(anchor)),
+            };
 
         public static Box2d Union(Box2d left, Box2d right)
         {