feat: Added componentsAtPoint() iterable (#1518)

doc/flame/components.md

@@ -190,6 +190,32 @@ void update(double dt) {
 ```
 
 
+### Querying components at a specific point on the screen
+
+The method `componentsAtPoint()` allows you to check which components have been rendered at a
+specific point on the screen. The returned value is an iterable which contains both the components
+and the coordinates of the query point in those components' local coordinates. The iterable
+retrieves the components in the front-to-back order, i.e. first the components in the front,
+followed by the components in the back.
+
+This method can only return components that implement the method `containsLocalPoint()`. The
+`PositionComponent` (which is the base class for many components in Flame) provides such an
+implementation. However, if you're defining a custom class that derives from `Component`, you'd have
+to implement the `containsLocalPoint()` method yourself.
+
+Here is an example of how `componentsAtPoint()` can be used:
+
+```dart
+void onDragUpdate(DragUpdateInfo info) {
+  game.componentsAtPoint(info.widget).forEach((p) {
+    if (p.component is DropTarget) {
+      p.component.highlight();
+    }
+  });
+}
+```
+
+
 ### PositionType
 If you want to create a HUD (Head-up display) or another component that isn't positioned in relation
 to the game coordinates, you can change the `PositionType` of the component.

examples/lib/stories/camera_and_viewport/camera_component_properties_example.dart

@@ -3,8 +3,9 @@ import 'dart:ui';
 import 'package:flame/components.dart';
 import 'package:flame/experimental.dart';
 import 'package:flame/game.dart' hide Viewport;
+import 'package:flame/input.dart';
 
-class CameraComponentPropertiesExample extends FlameGame {
+class CameraComponentPropertiesExample extends FlameGame with HasTappables {
   static const description = '''
     This example uses FixedSizeViewport which is dynamically sized and 
     positioned based on the size of the game widget.
@@ -13,6 +14,8 @@ class CameraComponentPropertiesExample extends FlameGame {
     green dot being the origin. The viewfinder uses custom anchor in order to
     declare its "center" half-way between the bottom left corner and the true
     center.
+    
+    Click at any point within the viewport to create a circle there.
   ''';
 
   CameraComponent? _camera;
@@ -41,6 +44,19 @@ class CameraComponentPropertiesExample extends FlameGame {
     _camera?.viewport.size = size * 0.7;
     _camera?.viewport.position = size * 0.6;
   }
+
+  @override
+  // ignore: must_call_super
+  void onTapDown(int pointerId, TapDownInfo info) {
+    final canvasPoint = info.eventPosition.widget;
+    for (final cp in componentsAtPoint(canvasPoint)) {
+      if (cp.component is Background) {
+        cp.component.add(
+          ExpandingCircle(cp.point.toOffset()),
+        );
+      }
+    }
+  }
 }
 
 class ViewportFrame extends Component {
@@ -64,7 +80,7 @@ class ViewportFrame extends Component {
 
 class Background extends Component {
   final bgPaint = Paint()..color = const Color(0xffff0000);
-  final originPaint = Paint()..color = const Color(0xff2f8750);
+  final originPaint = Paint()..color = const Color(0xff19bf57);
   final axisPaint = Paint()
     ..strokeWidth = 1
     ..style = PaintingStyle.stroke
@@ -85,4 +101,33 @@ class Background extends Component {
     canvas.drawLine(Offset.zero, const Offset(10, 0), axisPaint);
     canvas.drawCircle(Offset.zero, 1.0, originPaint);
   }
+
+  @override
+  bool containsLocalPoint(Vector2 point) => true;
+}
+
+class ExpandingCircle extends CircleComponent {
+  ExpandingCircle(Offset center)
+      : super(
+          position: Vector2(center.dx, center.dy),
+          anchor: Anchor.center,
+          radius: 0,
+          paint: Paint()
+            ..color = const Color(0xffffffff)
+            ..style = PaintingStyle.stroke
+            ..strokeWidth = 1,
+        );
+
+  static const maxRadius = 50;
+
+  @override
+  void update(double dt) {
+    radius += dt * 10;
+    if (radius >= maxRadius) {
+      removeFromParent();
+    } else {
+      final opacity = 1 - radius / maxRadius;
+      paint.color = const Color(0xffffffff).withOpacity(opacity);
+    }
+  }
 }

packages/flame/lib/components.dart

@@ -3,6 +3,7 @@ export 'src/anchor.dart';
 export 'src/collisions/has_collision_detection.dart';
 export 'src/collisions/hitboxes/screen_hitbox.dart';
 export 'src/components/component.dart';
+export 'src/components/component_point_pair.dart';
 export 'src/components/component_set.dart';
 export 'src/components/custom_painter_component.dart';
 export 'src/components/input/joystick_component.dart';

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

@@ -3,11 +3,16 @@ import 'dart:collection';
 
 import 'package:flutter/painting.dart';
 import 'package:meta/meta.dart';
+import 'package:vector_math/vector_math_64.dart';
 
-import '../../components.dart';
-import '../../game.dart';
-import '../../input.dart';
 import '../cache/value_cache.dart';
+import '../game/mixins/game.dart';
+import '../gestures/events.dart';
+import '../text.dart';
+import 'component_point_pair.dart';
+import 'component_set.dart';
+import 'mixins/coordinate_transform.dart';
+import 'position_type.dart';
 
 /// [Component]s are the basic building blocks for your game.
 ///
@@ -613,10 +618,56 @@ class Component {
     return (parent is T ? parent : parent?.findParent<T>()) as T?;
   }
 
-  /// Called to check whether the point is to be counted as within the component
+  /// Checks whether the [point] is within this component's bounds.
-  /// It needs to be overridden to have any effect, like it is in
+  ///
-  /// PositionComponent.
+  /// This method should be implemented for any component that has a visual
-  bool containsPoint(Vector2 point) => false;
+  /// representation and non-zero size. The [point] is in the local coordinate
+  /// space.
+  bool containsLocalPoint(Vector2 point) => false;
+
+  /// Same as [containsLocalPoint], but for a "global" [point].
+  ///
+  /// This will be deprecated in the future, due to the notion of "global" point
+  /// not being well-defined.
+  bool containsPoint(Vector2 point) => containsLocalPoint(point);
+
+  /// An iterable of descendant components intersecting the given point. The
+  /// [point] is in the local coordinate space.
+  ///
+  /// More precisely, imagine a ray originating at a certain point (x, y) on
+  /// the screen, and extending perpendicularly to the screen's surface into
+  /// your game's world. The purpose of this method is to find all components
+  /// that intersect with this ray, in the order from those that are closest to
+  /// the user to those that are farthest.
+  ///
+  /// The return value is an [Iterable] of `(component, point)` pairs, which
+  /// gives not only the components themselves, but also the points of
+  /// intersection, in their respective local coordinates.
+  ///
+  /// The default implementation relies on the [CoordinateTransform] interface
+  /// to translate from the parent's coordinate system into the local one. Make
+  /// sure that your component implements this interface if it alters the
+  /// coordinate system when rendering.
+  ///
+  /// If your component overrides [renderTree], then it almost certainly needs
+  /// to override this method as well, so that this method can find all rendered
+  /// components wherever they are.
+  Iterable<ComponentPointPair> componentsAtPoint(Vector2 point) sync* {
+    if (_children != null) {
+      for (final child in _children!.reversed()) {
+        Vector2? childPoint = point;
+        if (child is CoordinateTransform) {
+          childPoint = (child as CoordinateTransform).parentToLocal(point);
+        }
+        if (childPoint != null) {
+          yield* child.componentsAtPoint(childPoint);
+        }
+      }
+    }
+    if (containsLocalPoint(point)) {
+      yield ComponentPointPair(this, point);
+    }
+  }
 
   /// Usually this is not something that the user would want to call since the
   /// component list isn't re-ordered when it is called.

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

@@ -0,0 +1,27 @@
+import 'dart:ui';
+
+import 'package:meta/meta.dart';
+import 'package:vector_math/vector_math_64.dart';
+
+import 'component.dart';
+
+/// A simple tuple of a component and a point. This is a helper class for the
+/// [Component.componentsAtPoint] method.
+@immutable
+class ComponentPointPair {
+  const ComponentPointPair(this.component, this.point);
+  final Component component;
+  final Vector2 point;
+
+  @override
+  bool operator ==(Object other) =>
+      other is ComponentPointPair &&
+      other.component == component &&
+      other.point == point;
+
+  @override
+  int get hashCode => hashValues(component, point);
+
+  @override
+  String toString() => '<$component, $point>';
+}

packages/flame/lib/src/components/mixins/coordinate_transform.dart

@@ -0,0 +1,24 @@
+import 'package:vector_math/vector_math_64.dart';
+import '../component.dart';
+
+/// Interface to be implemented by components that perform a coordinate change.
+///
+/// Any [Component] that does any coordinate transformation of the canvas during
+/// rendering should consider implementing this interface in order to describe
+/// how the points from the parent's coordinate system relate to the component's
+/// local coordinate system.
+///
+/// This interface assumes that the component performs a "uniform" coordinate
+/// transformation, that is, the transform applies to all children of the
+/// component equally. If that is not the case (for example, the component does
+/// different transformations for some of its children), then that component
+/// must implement [Component.componentsAtPoint] method instead.
+///
+/// The two methods of this interface convert between the parent's coordinate
+/// space and the local coordinates. The methods may also return `null`,
+/// indicating that the given cannot be mapped to any local/parent point.
+abstract class CoordinateTransform {
+  Vector2? parentToLocal(Vector2 point);
+
+  Vector2? localToParent(Vector2 point);
+}

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

@@ -8,6 +8,7 @@ import '../extensions/vector2.dart';
 import '../game/notifying_vector2.dart';
 import '../game/transform2d.dart';
 import 'component.dart';
+import 'mixins/coordinate_transform.dart';
 
 /// A [Component] implementation that represents an object that can be
 /// freely moved around the screen, rotated, and scaled.
@@ -59,7 +60,12 @@ import 'component.dart';
 /// do not specify the size of a PositionComponent, then it will be
 /// equal to zero and the component won't be able to respond to taps.
 class PositionComponent extends Component
-    implements AnchorProvider, AngleProvider, PositionProvider, ScaleProvider {
+    implements
+        AnchorProvider,
+        AngleProvider,
+        PositionProvider,
+        ScaleProvider,
+        CoordinateTransform {
   PositionComponent({
     Vector2? position,
     Vector2? size,
@@ -214,14 +220,24 @@ class PositionComponent extends Component
   /// component. The top and the left borders of the component are inclusive,
   /// while the bottom and the right borders are exclusive.
   @override
-  bool containsPoint(Vector2 point) {
+  bool containsLocalPoint(Vector2 point) {
-    final local = absoluteToLocal(point);
+    return (point.x >= 0) &&
-    return (local.x >= 0) &&
+        (point.y >= 0) &&
-        (local.y >= 0) &&
+        (point.x < _size.x) &&
-        (local.x < _size.x) &&
+        (point.y < _size.y);
-        (local.y < _size.y);
   }
 
+  @override
+  bool containsPoint(Vector2 point) {
+    return containsLocalPoint(absoluteToLocal(point));
+  }
+
+  @override
+  Vector2 parentToLocal(Vector2 point) => transform.globalToLocal(point);
+
+  @override
+  Vector2 localToParent(Vector2 point) => transform.localToGlobal(point);
+
   /// Convert local coordinates of a point [point] inside the component
   /// into the parent's coordinate space.
   Vector2 positionOf(Vector2 point) {

packages/flame/lib/src/experimental/camera_component.dart

@@ -4,6 +4,7 @@ import 'package:meta/meta.dart';
 import 'package:vector_math/vector_math_64.dart';
 
 import '../components/component.dart';
+import '../components/component_point_pair.dart';
 import '../components/position_component.dart';
 import '../effects/controllers/effect_controller.dart';
 import '../effects/move_effect.dart';
@@ -92,7 +93,7 @@ class CameraComponent extends Component {
       viewport.clip(canvas);
       try {
         currentCameras.add(this);
-        canvas.transform(viewfinder.transformMatrix.storage);
+        canvas.transform(viewfinder.transform.transformMatrix.storage);
         world.renderFromCamera(canvas);
         viewfinder.renderTree(canvas);
       } finally {
@@ -105,6 +106,24 @@ class CameraComponent extends Component {
     canvas.restore();
   }
 
+  @override
+  Iterable<ComponentPointPair> componentsAtPoint(Vector2 point) sync* {
+    final viewportPoint = point - viewport.position;
+    if (world.isMounted && currentCameras.length < maxCamerasDepth) {
+      if (viewport.containsPoint(viewportPoint)) {
+        try {
+          currentCameras.add(this);
+          final worldPoint = viewfinder.transform.globalToLocal(viewportPoint);
+          yield* world.componentsAtPointFromCamera(worldPoint);
+          yield* viewfinder.componentsAtPoint(worldPoint);
+        } finally {
+          currentCameras.removeLast();
+        }
+      }
+    }
+    yield* viewport.componentsAtPoint(viewportPoint);
+  }
+
   /// A camera that currently performs rendering.
   ///
   /// This variable is set to `this` when we begin rendering the world through

packages/flame/lib/src/experimental/circular_viewport.dart

@@ -12,14 +12,19 @@ class CircularViewport extends Viewport {
   }
 
   Path _clipPath = Path();
+  double _radiusSquared = 0;
 
   @override
   void clip(Canvas canvas) => canvas.clipPath(_clipPath, doAntiAlias: false);
 
+  @override
+  bool containsLocalPoint(Vector2 point) => point.length2 <= _radiusSquared;
+
   @override
   void onViewportResize() {
+    assert(size.x == size.y, 'Viewport shape is not circular: $size');
     final x = size.x / 2;
-    final y = size.y / 2;
+    _clipPath = Path()..addOval(Rect.fromLTRB(-x, -x, x, x));
-    _clipPath = Path()..addOval(Rect.fromLTRB(-x, -y, x, y));
+    _radiusSquared = x * x;
   }
 }

packages/flame/lib/src/experimental/fixed_aspect_ratio_viewport.dart

@@ -23,7 +23,12 @@ class FixedAspectRatioViewport extends Viewport {
   }
 
   @override
-  void clip(Canvas canvas) => canvas.clipRect(_clipRect);
+  void clip(Canvas canvas) => canvas.clipRect(_clipRect, doAntiAlias: false);
+
+  @override
+  bool containsLocalPoint(Vector2 point) {
+    return point.x.abs() <= size.x / 2 && point.y.abs() <= size.y / 2;
+  }
 
   @override
   void onViewportResize() {

packages/flame/lib/src/experimental/fixed_size_viewport.dart

@@ -24,6 +24,11 @@ class FixedSizeViewport extends Viewport {
   @override
   void clip(Canvas canvas) => canvas.clipRect(_clipRect, doAntiAlias: false);
 
+  @override
+  bool containsLocalPoint(Vector2 point) {
+    return point.x.abs() <= size.x / 2 && point.y.abs() <= size.y / 2;
+  }
+
   @override
   void onViewportResize() {
     final x = size.x / 2;

packages/flame/lib/src/experimental/max_viewport.dart

@@ -21,6 +21,9 @@ class MaxViewport extends Viewport {
   @override
   void clip(Canvas canvas) {}
 
+  @override
+  bool containsLocalPoint(Vector2 point) => true;
+
   @override
   void onViewportResize() {}
 }

packages/flame/lib/src/experimental/viewfinder.dart

@@ -21,7 +21,7 @@ class Viewfinder extends Component
   final Transform2D _transform = Transform2D();
 
   @internal
-  Matrix4 get transformMatrix => _transform.transformMatrix;
+  Transform2D get transform => _transform;
 
   /// The game coordinates of a point that is to be positioned at the center
   /// of the viewport.

packages/flame/lib/src/experimental/viewport.dart

@@ -66,6 +66,14 @@ abstract class Viewport extends Component implements PositionProvider {
   /// This API must be implemented by all viewports.
   void clip(Canvas canvas);
 
+  /// Tests whether the given point lies within the viewport.
+  ///
+  /// This method must be consistent with the action of [clip], in the sense
+  /// that [containsLocalPoint] must return true if and only if that point on
+  /// the canvas is not clipped by [clip].
+  @override
+  bool containsLocalPoint(Vector2 point);
+
   /// Override in order to perform a custom action upon resize.
   ///
   /// A typical use-case would be to adjust the viewport's clip mask to match

packages/flame/lib/src/experimental/world.dart

@@ -1,8 +1,10 @@
 import 'dart:ui';
 
 import 'package:meta/meta.dart';
+import 'package:vector_math/vector_math_64.dart';
 
 import '../components/component.dart';
+import '../components/component_point_pair.dart';
 import 'camera_component.dart';
 
 /// The root component for all game world elements.
@@ -20,4 +22,14 @@ class World extends Component {
     assert(CameraComponent.currentCamera != null);
     super.renderTree(canvas);
   }
+
+  @override
+  Iterable<ComponentPointPair> componentsAtPoint(Vector2 point) {
+    return const Iterable.empty();
+  }
+
+  @internal
+  Iterable<ComponentPointPair> componentsAtPointFromCamera(Vector2 point) {
+    return super.componentsAtPoint(point);
+  }
 }

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

@@ -131,8 +131,8 @@ class FlameGame extends Component with Game {
 
   /// Whether a point is within the boundaries of the visible part of the game.
   @override
-  bool containsPoint(Vector2 p) {
+  bool containsLocalPoint(Vector2 p) {
-    return p.x > 0 && p.y > 0 && p.x < size.x && p.y < size.y;
+    return p.x >= 0 && p.y >= 0 && p.x < size.x && p.y < size.y;
   }
 
   /// Returns the current time in seconds with microseconds precision.

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

@@ -85,6 +85,14 @@ class CircleComponent extends ShapeComponent {
         scaledRadius * scaledRadius;
   }
 
+  @override
+  bool containsLocalPoint(Vector2 point) {
+    final radius = size.x / 2;
+    final dx = point.x - radius;
+    final dy = point.y - radius;
+    return dx * dx + dy * dy <= radius * radius;
+  }
+
   /// Returns the locus of points in which the provided line segment intersect
   /// the circle.
   ///
@@ -94,7 +102,7 @@ class CircleComponent extends ShapeComponent {
     LineSegment line, {
     double epsilon = double.minPositive,
   }) {
-    double sq(double x) => pow(x, 2).toDouble();
+    double sq(double x) => x * x;
 
     final cx = absoluteCenter.x;
     final cy = absoluteCenter.y;

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

@@ -1,13 +1,16 @@
 import 'dart:math';
-import 'dart:ui' hide Canvas;
+import 'dart:ui';
 
 import 'package:collection/collection.dart';
 import 'package:meta/meta.dart';
 
-import '../../cache.dart';
+import '../anchor.dart';
-import '../../components.dart';
+import '../cache/value_cache.dart';
-import '../../extensions.dart';
+import '../components/component.dart';
-import '../../geometry.dart';
+import '../extensions/rect.dart';
+import '../extensions/vector2.dart';
+import 'line_segment.dart';
+import 'shape_component.dart';
 
 class PolygonComponent extends ShapeComponent {
   final List<Vector2> _vertices;
@@ -221,6 +224,23 @@ class PolygonComponent extends ShapeComponent {
     return true;
   }
 
+  @override
+  bool containsLocalPoint(Vector2 point) {
+    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;
+      if (isOutside) {
+        return false;
+      }
+    }
+    return true;
+  }
+
   /// Return all vertices as [LineSegment]s that intersect [rect], if [rect]
   /// is null return all vertices as [LineSegment]s.
   List<LineSegment> possibleIntersectionVertices(Rect? rect) {

packages/flame/test/components/component_test.dart

@@ -501,6 +501,56 @@ void main() {
         },
       );
     });
+
+    group('componentsAtPoint', () {
+      testWithFlameGame('nested components', (game) async {
+        final componentA = PositionComponent()
+          ..size = Vector2(200, 150)
+          ..scale = Vector2.all(2)
+          ..position = Vector2(350, 50)
+          ..addToParent(game);
+        final componentB = CircleComponent(radius: 10)
+          ..position = Vector2(150, 75)
+          ..anchor = Anchor.center
+          ..addToParent(componentA);
+        await game.ready();
+
+        expect(
+          game.componentsAtPoint(Vector2.zero()).toList(),
+          [ComponentPointPair(game, Vector2.zero())],
+        );
+        expect(
+          game.componentsAtPoint(Vector2(400, 100)).toList(),
+          [
+            ComponentPointPair(componentA, Vector2(25, 25)),
+            ComponentPointPair(game, Vector2(400, 100)),
+          ],
+        );
+        expect(
+          game.componentsAtPoint(Vector2(650, 200)).toList(),
+          [
+            ComponentPointPair(componentB, Vector2(10, 10)),
+            ComponentPointPair(componentA, Vector2(150, 75)),
+            ComponentPointPair(game, Vector2(650, 200)),
+          ],
+        );
+        expect(
+          game.componentsAtPoint(Vector2(664, 214)).toList(),
+          [
+            ComponentPointPair(componentB, Vector2(17, 17)),
+            ComponentPointPair(componentA, Vector2(157, 82)),
+            ComponentPointPair(game, Vector2(664, 214)),
+          ],
+        );
+        expect(
+          game.componentsAtPoint(Vector2(664, 216)).toList(),
+          [
+            ComponentPointPair(componentA, Vector2(157, 83)),
+            ComponentPointPair(game, Vector2(664, 216)),
+          ],
+        );
+      });
+    });
   });
 }