fix: Misalignment of the hittest area of PolygonHitbox (#2930)

When performing a pointer hit test using PolygonHitbox, there may be a
discrepancy between the expected range and the range in which the hit
test succeeds. If the polygon shape has an offset at the top left, the
hit test will behave as if there is no offset.

Investigation revealed that the cause was in the calculation of
containsLocalPoint() in the PolygonComponent. The unnecessary offset
calculation was removed, and the hit test is now performed in the
expected range.


Closes #2758

---------

Co-authored-by: Lukas Klingsbo <me@lukas.fyi>

packages/flame/lib/src/geometry/polygon_component.dart

@@ -231,9 +231,8 @@ class PolygonComponent extends ShapeComponent {
     }
     for (var i = 0; i < _vertices.length; i++) {
       final edge = getEdge(i, vertices: vertices);
-      final isOutside = (edge.to.x - edge.from.x) *
-                  (point.y - edge.from.y + _topLeft.y) -
-              (point.x - edge.from.x + _topLeft.x) * (edge.to.y - edge.from.y) >
+      final isOutside = (edge.to.x - edge.from.x) * (point.y - edge.from.y) -
+              (point.x - edge.from.x) * (edge.to.y - edge.from.y) >
           0;
       if (isOutside) {
         return false;

packages/flame/test/components/shape_component_test.dart

@@ -43,6 +43,19 @@ void main() {
       );
     });
 
+    test('polygon contains point in local', () {
+      final polygon = PolygonComponent(
+        [
+          Vector2(0.5, 0.5),
+          Vector2(0.5, 1.5),
+          Vector2(1.5, 1.5),
+          Vector2(1.5, 0.5),
+        ],
+      );
+      expect(polygon.containsLocalPoint(Vector2(0.25, 0.25)), isFalse);
+      expect(polygon.containsLocalPoint(Vector2(0.75, 0.75)), isTrue);
+    });
+
     test('rotated circle does not contain point', () {
       final component = CircleComponent(
         radius: 1.0,