fix: Absolute angle takes into account BodyComponent ancestors too (#…

…2678)

Currently, the implementation of the `absoluteAngle` getter in
`PositionComponent` only takes into account `PositionComponent`
ancestors. The implementation simply runs through the whole hierarchy
summing up the relative angles.

This gives a wrong result with Forge2D because `BodyComponent`s have
angles too: in the common situation where a `PositionComponent` (e.g. a
`SpriteComponent`) is the child of a `BodyComponent`, the
`BodyComponent`'s rotation is ignored when computing the
`absoluteAngle`.

The fix simply introduces a new minimal interface `HasAngle` that both
`PositionComponent` and `BodyComponent` implement (`PositionComponent`
implements it automatically via `AngleProvider`), and reimplements
`absoluteAngle` so that it considers all ancestors with an angle and not
just the `PositionComponent` ones.

packages/flame/lib/effects.dart

@@ -30,9 +30,11 @@ export 'src/effects/provider_interfaces.dart'
     show
         AnchorProvider,
         AngleProvider,
+        ReadOnlyAngleProvider,
         PositionProvider,
         ScaleProvider,
         SizeProvider,
+        ReadOnlySizeProvider,
         OpacityProvider;
 export 'src/effects/remove_effect.dart';
 export 'src/effects/rotate_effect.dart';

packages/flame/lib/src/components/core/component.dart

@@ -826,8 +826,8 @@ class Component {
     assert(isLoaded && !isLoading);
     _setMountingBit();
     onGameResize(_parent!.findGame()!.canvasSize);
-    if (_parent is ReadonlySizeProvider) {
-      onParentResize((_parent! as ReadonlySizeProvider).size);
+    if (_parent is ReadOnlySizeProvider) {
+      onParentResize((_parent! as ReadOnlySizeProvider).size);
     }
     if (isRemoved) {
       _clearRemovedBit();

packages/flame/lib/src/components/input/hud_margin_component.dart

@@ -35,15 +35,15 @@ class HudMarginComponent extends PositionComponent {
   /// from the edges of the viewport can be used instead.
   EdgeInsets? margin;
 
-  late ReadonlySizeProvider? _sizeProvider;
+  late ReadOnlySizeProvider? _sizeProvider;
 
   @override
   @mustCallSuper
   void onMount() {
     super.onMount();
     _sizeProvider =
-        ancestors().firstWhereOrNull((c) => c is ReadonlySizeProvider)
-            as ReadonlySizeProvider?;
+        ancestors().firstWhereOrNull((c) => c is ReadOnlySizeProvider)
+            as ReadOnlySizeProvider?;
     assert(
       _sizeProvider != null,
       'The parent of a HudMarginComponent needs to provide a size, for example '

packages/flame/lib/src/components/position_component.dart

@@ -231,7 +231,7 @@ class PositionComponent extends Component
   double get absoluteAngle {
     // TODO(spydon): take scale into consideration
     return ancestors(includeSelf: true)
-        .whereType<PositionComponent>()
+        .whereType<ReadOnlyAngleProvider>()
         .map((c) => c.angle)
         .sum;
   }

packages/flame/lib/src/effects/provider_interfaces.dart

@@ -34,9 +34,14 @@ abstract class ScaleProvider {
   set scale(Vector2 value);
 }
 
-/// Interface for a component that can be affected by rotation effects.
-abstract class AngleProvider {
+/// Interface for a class that has [angle] property which can be read but not
+/// modified.
+abstract class ReadOnlyAngleProvider {
   double get angle;
+}
+
+/// Interface for a component that can be affected by rotation effects.
+abstract class AngleProvider extends ReadOnlyAngleProvider {
   set angle(double value);
 }
 
@@ -48,12 +53,12 @@ abstract class AnchorProvider {
 
 /// Interface for a class that has [size] property which can be read but not
 /// modified.
-abstract class ReadonlySizeProvider {
+abstract class ReadOnlySizeProvider {
   Vector2 get size;
 }
 
 /// Interface for a component that can be affected by size effects.
-abstract class SizeProvider extends ReadonlySizeProvider {
+abstract class SizeProvider extends ReadOnlySizeProvider {
   set size(Vector2 value);
 }
 

packages/flame/lib/src/game/flame_game.dart

@@ -20,7 +20,7 @@ import 'package:meta/meta.dart';
 /// It is based on the Flame Component System (also known as FCS).
 class FlameGame extends ComponentTreeRoot
     with Game
-    implements ReadonlySizeProvider {
+    implements ReadOnlySizeProvider {
   FlameGame({
     super.children,
     Camera? camera,

packages/flame/lib/src/layout/align_component.dart

@@ -108,7 +108,7 @@ class AlignComponent extends PositionComponent {
   @override
   void onMount() {
     assert(
-      parent is ReadonlySizeProvider,
+      parent is ReadOnlySizeProvider,
       "An AlignComponent's parent must have a size",
     );
   }

packages/flame_forge2d/lib/body_component.dart

@@ -1,6 +1,7 @@
 import 'dart:ui';
 
 import 'package:flame/components.dart' hide World;
+import 'package:flame/effects.dart' show ReadOnlyAngleProvider;
 import 'package:flame/extensions.dart';
 import 'package:flame/game.dart';
 import 'package:flame_forge2d/forge2d_game.dart';
@@ -11,7 +12,8 @@ import 'package:forge2d/forge2d.dart' hide Timer, Vector2;
 /// it is a good idea to turn on [debugMode] for it so that the bodies can be
 /// seen
 abstract class BodyComponent<T extends Forge2DGame> extends Component
-    with HasGameRef<T>, HasPaint {
+    with HasGameRef<T>, HasPaint
+    implements ReadOnlyAngleProvider {
   BodyComponent({
     Paint? paint,
     super.children,
@@ -46,10 +48,14 @@ abstract class BodyComponent<T extends Forge2DGame> extends Component
   }
 
   World get world => gameRef.world;
+
   // TODO(Lukas): Use CameraComponent here instead.
   // ignore: deprecated_member_use
   Camera get camera => gameRef.camera;
+
   Vector2 get center => body.worldCenter;
+
+  @override
   double get angle => body.angle;
 
   /// The matrix used for preparing the canvas

packages/flame_forge2d/test/body_component_test.dart

@@ -1,5 +1,6 @@
 // ignore_for_file: deprecated_member_use
 
+import 'package:flame/components.dart' show PositionComponent;
 import 'package:flame/extensions.dart';
 import 'package:flame_forge2d/flame_forge2d.dart';
 import 'package:flame_test/flame_test.dart';
@@ -325,5 +326,43 @@ void main() {
         ).called(1);
       });
     });
+
+    group('PositionComponent parented by BodyComponent', () {
+      final flameTester = FlameTester(Forge2DGame.new);
+
+      flameTester.testGameWidget(
+        'absoluteAngle',
+        setUp: (game, tester) async {
+          // Creates a body with an angle of 2 radians
+          final body = game.world.createBody(BodyDef(angle: 2.0));
+          final shape = EdgeShape()
+            ..set(
+              Vector2.zero(),
+              Vector2.all(10),
+            );
+          body.createFixture(FixtureDef(shape));
+          final bodyComponent = _TestBodyComponent()..body = body;
+
+          // Creates a positional component with an angle of 1 radians
+          final positionComponent = PositionComponent(angle: 1.0);
+
+          // Creates a hierarchy: game > bodyComponent > positionComponent
+          bodyComponent.addToParent(game);
+          positionComponent.addToParent(bodyComponent);
+
+          await game.ready();
+
+          // Checks the hierarchy
+          expect(game.contains(bodyComponent), true);
+          expect(bodyComponent.contains(positionComponent), true);
+          expect(game.children.length, 1);
+          expect(bodyComponent.children.length, 1);
+          expect(positionComponent.children.length, 0);
+
+          // Expects the absolute angle to be (2 + 1) radians
+          expect(positionComponent.absoluteAngle, 3.0);
+        },
+      );
+    });
   });
 }