fix: PolygonComponent.containsLocalPoint to use anchor (#2953)

Apparently `PolygonComponent.containsLocalPoint` has to take the anchor
into consideration, I have no idea how nobody noticed this before...

packages/flame/example/lib/main.dart

@@ -6,28 +6,28 @@ import 'package:flame/game.dart';
 import 'package:flame/palette.dart';
 import 'package:flutter/material.dart';
 
+/// This example simply adds a rotating white square on the screen.
+/// If you press on a square, it will be removed.
+/// If you press anywhere else, another square will be added.
 void main() {
   runApp(
     GameWidget(
-      game: MyGame(),
+      game: FlameGame(world: MyWorld()),
     ),
   );
 }
 
-/// This example simply adds a rotating white square on the screen.
-/// If you press on a square, it will be removed.
-/// If you press anywhere else, another square will be added.
-class MyGame extends FlameGame with TapCallbacks {
+class MyWorld extends World with TapCallbacks {
   @override
   Future<void> onLoad() async {
-    add(Square(size / 2));
+    add(Square(Vector2.zero()));
   }
 
   @override
   void onTapDown(TapDownEvent event) {
     super.onTapDown(event);
     if (!event.handled) {
-      final touchPoint = event.canvasPosition;
+      final touchPoint = event.localPosition;
       add(Square(touchPoint));
     }
   }
@@ -48,13 +48,6 @@ class Square extends RectangleComponent with TapCallbacks {
           anchor: Anchor.center,
         );
 
-  @override
-  void update(double dt) {
-    super.update(dt);
-    angle += speed * dt;
-    angle %= 2 * math.pi;
-  }
-
   @override
   Future<void> onLoad() async {
     super.onLoad();
@@ -74,6 +67,13 @@ class Square extends RectangleComponent with TapCallbacks {
     );
   }
 
+  @override
+  void update(double dt) {
+    super.update(dt);
+    angle += speed * dt;
+    angle %= 2 * math.pi;
+  }
+
   @override
   void onTapDown(TapDownEvent event) {
     removeFromParent();

packages/flame/lib/src/anchor.dart

@@ -49,12 +49,14 @@ class Anchor {
   Vector2 toOtherAnchorPosition(
     Vector2 position,
     Anchor otherAnchor,
-    Vector2 size,
-  ) {
+    Vector2 size, {
+    Vector2? out,
+  }) {
     if (this == otherAnchor) {
       return position;
     } else {
-      return Vector2(otherAnchor.x - x, otherAnchor.y - y)
+      return (out ?? Vector2.zero())
+        ..setValues(otherAnchor.x - x, otherAnchor.y - y)
         ..multiply(size)
         ..add(position);
     }

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

@@ -226,14 +226,18 @@ class PolygonComponent extends ShapeComponent {
 
   @override
   bool containsLocalPoint(Vector2 point) {
+    // Take anchor into consideration.
+    final localPoint =
+        anchor.toOtherAnchorPosition(point, Anchor.topLeft, size);
     if (size.x == 0 || size.y == 0) {
       return false;
     }
     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) -
-              (point.x - edge.from.x) * (edge.to.y - edge.from.y) >
-          0;
+      final isOutside =
+          (edge.to.x - edge.from.x) * (localPoint.y - edge.from.y) -
+                  (localPoint.x - edge.from.x) * (edge.to.y - edge.from.y) >
+              0;
       if (isOutside) {
         return false;
       }

packages/flame/test/components/shape_component_test.dart

@@ -56,6 +56,33 @@ void main() {
       expect(polygon.containsLocalPoint(Vector2(0.75, 0.75)), isTrue);
     });
 
+    test('rectangle contains point in local with anchor', () {
+      final rectangle = RectangleComponent(
+        position: Vector2.zero(),
+        size: Vector2.all(10),
+        anchor: Anchor.center,
+      );
+      expect(rectangle.containsLocalPoint(Vector2.zero()), isTrue);
+      expect(rectangle.containsLocalPoint(Vector2.all(5)), isTrue);
+      expect(rectangle.containsLocalPoint(Vector2.all(10)), isTrue);
+      expect(rectangle.containsLocalPoint(Vector2(10, 0)), isTrue);
+      expect(rectangle.containsLocalPoint(Vector2(0, 10)), isTrue);
+    });
+
+    test('angled rectangle contains point in local with anchor', () {
+      final rectangle = RectangleComponent(
+        position: Vector2.zero(),
+        size: Vector2.all(10),
+        angle: pi / 4,
+        anchor: Anchor.center,
+      );
+      expect(rectangle.containsLocalPoint(Vector2.zero()), isTrue);
+      expect(rectangle.containsLocalPoint(Vector2.all(5)), isTrue);
+      expect(rectangle.containsLocalPoint(Vector2.all(10)), isTrue);
+      expect(rectangle.containsLocalPoint(Vector2(10, 0)), isTrue);
+      expect(rectangle.containsLocalPoint(Vector2(0, 10)), isTrue);
+    });
+
     test('rotated circle does not contain point', () {
       final component = CircleComponent(
         radius: 1.0,