refactor: store adjusted height

packages/pinball_components/lib/src/components/ball.dart

@@ -104,10 +104,10 @@ class Ball<T extends Forge2DGame> extends BodyComponent<T>
     const maxShrinkAmount = BoardDimensions.perspectiveShrinkFactor;
 
     final adjustedYPosition = body.position.y + (boardHeight / 2);
-    final adjustedHeight = (1 / (1 - maxShrinkAmount)) * boardHeight;
 
-    final scaleFactor =
-        ((boardHeight - adjustedYPosition) / adjustedHeight) + maxShrinkAmount;
+    final scaleFactor = ((boardHeight - adjustedYPosition) /
+            BoardDimensions.shrinkAdjustedHeight) +
+        maxShrinkAmount;
 
     body.fixtures.first.shape.radius = (size.x / 2) * scaleFactor;
     _spriteComponent.scale = Vector2.all(scaleFactor);

packages/pinball_components/lib/src/components/board_dimensions.dart

@@ -21,4 +21,8 @@ class BoardDimensions {
 
   /// Factor the board shrinks by from the closest point to the farthest.
   static const perspectiveShrinkFactor = 0.63;
+
+  /// Board height based on the [perspectiveShrinkFactor].
+  static final shrinkAdjustedHeight =
+      (1 / (1 - perspectiveShrinkFactor)) * size.y;
 }

packages/pinball_components/test/src/components/board_dimensions_test.dart

@@ -19,5 +19,9 @@ void main() {
     test('has perspectiveShrinkFactor', () {
       expect(BoardDimensions.perspectiveShrinkFactor, equals(0.63));
     });
+
+    test('has shrinkAdjustedHeight', () {
+      expect(BoardDimensions.shrinkAdjustedHeight, isNotNull);
+    });
   });
 }