perf: Switch from forEach to regular for-loops for about 30% improvem…

…ent in raw update performance (#3472)

Replaces uses of `.forEach()` with regular `for` loops. This has
significant impact on performance in hot paths such as
`Component.updateTree()` and `Component.renderTree()`.

![Updating
Components](https://github.com/user-attachments/assets/e183ce4c-5b37-45d9-ad81-a0a35719e0dd)

In the graph above, you see 50 runs of
`benchmark/update_components_benchmark.dart`. The forEach results are
blue, the for-loop results are green. I could see this effect after just
replacing the `forEach` calls in `component.dart`. Data
[here](https://docs.google.com/spreadsheets/d/e/2PACX-1vRk_yGmLN6o0oqSUWDBh7ODx7B8EIToeahZcZBS3VKHX8AbEnmrgmEqDt98cZLoBjIKQX3MlOc0XwsP/pubhtml).

> Aside for posterity: `for i in {1..50}; do flutter test
benchmark/main.dart --no-pub -r silent 2>/dev/null >>
benchmarks_for_loop.txt; done`, then get the data from the text file.

I went ahead and replaced additional `forEach` calls elsewhere in the
engine codebase, but there was no additional effect on the benchmark.
Still, I kept those changes in. I only replaced `forEach` in places that
seemed relatively hot (e.g. `ComponentSet.reorder()`). There are more
`forEach` calls in the codebase but those seem fine to me as they aren't
likely to be called too often.

It should be noted that I needed to update the benchmark to add children
to the components. Every `_BenchmarkComponent` now has 10 children. This
feels a bit more realistic use of the framework than having a flat array
of components with no children. By changing the benchmark code in this
way, I made it a bit slower, so I'm not sure if the effect will be seen
in the CI/CD.

I also tried whether the change will have effect on my game's benchmark
(which is a lot more involved and uses `flutter driver` to test the
whole game in AOT mode). For the game, the effect is negligible but that
was kind of expected since my game spends a significant amount of its
CPU time on AI, raycasting, smoke simulation and drawVertices, none of
which really depend on the speed of the engine `update()` mechanism.

---------

Co-authored-by: Erick <[email protected]>

packages/flame/benchmark/update_components_benchmark.dart

@@ -7,6 +7,7 @@ import 'package:flame/game.dart';
 const _amountComponents = 1000;
 const _amountTicks = 2000;
 const _amountInputs = 500;
+const _amountChildren = 10;
 
 class UpdateComponentsBenchmark extends AsyncBenchmarkBase {
   final Random random;
@@ -65,6 +66,13 @@ class _BenchmarkComponent extends PositionComponent {
 
   _BenchmarkComponent(this.id);
 
+  @override
+  Future<void> onLoad() async {
+    for (var i = 0; i < _amountChildren; i++) {
+      await add(PositionComponent(position: Vector2(i * 2, 0)));
+    }
+  }
+
   void input({
     required int xDirection,
     required bool doJump,

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

@@ -91,7 +91,9 @@ abstract class Viewport extends Component
     }
     onViewportResize();
     if (hasChildren) {
-      children.forEach((child) => child.onParentResize(_size));
+      for (final child in children) {
+        child.onParentResize(_size);
+      }
     }
   }
 

packages/flame/lib/src/collisions/hitboxes/shape_hitbox.dart

@@ -89,10 +89,12 @@ mixin ShapeHitbox on ShapeComponent implements Hitbox<ShapeHitbox> {
       _validAabb = false;
       onAabbChanged?.call();
     };
-    ancestors(includeSelf: true).whereType<PositionComponent>().forEach((c) {
-      _transformAncestors.add(c.transform);
-      c.transform.addListener(_transformListener);
-    });
+    final positionComponents =
+        ancestors(includeSelf: true).whereType<PositionComponent>();
+    for (final ancestor in positionComponents) {
+      _transformAncestors.add(ancestor.transform);
+      ancestor.transform.addListener(_transformListener);
+    }
 
     if (shouldFillParent) {
       _parentSizeListener = () {

packages/flame/lib/src/collisions/standard_collision_detection.dart

@@ -167,7 +167,11 @@ class StandardCollisionDetection<B extends Broadphase<ShapeHitbox>>
     List<ShapeHitbox>? ignoreHitboxes,
     List<RaycastResult<ShapeHitbox>>? out,
   }) sync* {
-    out?.forEach((e) => e.reset());
+    if (out != null) {
+      for (final result in out) {
+        result.reset();
+      }
+    }
     var currentRay = ray;
     for (var i = 0; i < maxDepth; i++) {
       final hasResultObject = (out?.length ?? 0) > i;

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

@@ -524,7 +524,12 @@ class Component {
   /// priority of the direct siblings, not the children or the ancestors.
   void updateTree(double dt) {
     update(dt);
-    _children?.forEach((c) => c.updateTree(dt));
+    final children = _children;
+    if (children != null) {
+      for (final child in children) {
+        child.updateTree(dt);
+      }
+    }
   }
 
   /// This method will be invoked from lifecycle if [child] has been added
@@ -535,7 +540,12 @@ class Component {
 
   void renderTree(Canvas canvas) {
     render(canvas);
-    _children?.forEach((c) => c.renderTree(canvas));
+    final children = _children;
+    if (children != null) {
+      for (final child in children) {
+        child.renderTree(canvas);
+      }
+    }
 
     // Any debug rendering should be rendered on top of everything
     if (debugMode) {
@@ -868,11 +878,14 @@ class Component {
   @mustCallSuper
   @internal
   void handleResize(Vector2 size) {
-    _children?.forEach((child) {
-      if (child.isLoading || child.isLoaded) {
-        child.onGameResize(size);
+    final children = _children;
+    if (children != null) {
+      for (final child in children) {
+        if (child.isLoading || child.isLoaded) {
+          child.onGameResize(size);
+        }
       }
-    });
+    }
   }
 
   FutureOr<void> _startLoading() {

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

@@ -106,6 +106,8 @@ class ComponentSet extends QueryableOrderedSet<Component> {
     final elements = toList();
     // bypass the wrapper because the components are already added
     super.clear();
-    elements.forEach(super.add);
+    for (final element in elements) {
+      super.add(element);
+    }
   }
 }

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

@@ -158,12 +158,12 @@ class ComponentTreeRoot extends Component {
   @internal
   void handleResize(Vector2 size) {
     super.handleResize(size);
-    _queue.forEach((event) {
+    for (final event in _queue) {
       if ((event.kind == _LifecycleEventKind.add) &&
           (event.child!.isLoading || event.child!.isLoaded)) {
         event.child!.onGameResize(size);
       }
-    });
+    }
   }
 
   @mustCallSuper

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

@@ -208,9 +208,12 @@ class _MultiPaintOpacityProvider<T extends Object> implements OpacityProvider {
       maxOpacity = max(target.getOpacity(paintId: paintId), maxOpacity);
     }
     if (includeLayers) {
-      target.paintLayersInternal?.forEach(
-        (paint) => maxOpacity = max(paint.color.a, maxOpacity),
-      );
+      final targetLayers = target.paintLayersInternal;
+      if (targetLayers != null) {
+        for (final paint in targetLayers) {
+          maxOpacity = max(paint.color.a, maxOpacity);
+        }
+      }
     }
 
     return maxOpacity;

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

@@ -1,5 +1,4 @@
 import 'dart:math' as math;
-
 import 'dart:ui' hide Offset;
 
 import 'package:collection/collection.dart';
@@ -195,7 +194,9 @@ class PositionComponent extends Component
   set size(Vector2 size) {
     _size.setFrom(size);
     if (hasChildren) {
-      children.forEach((child) => child.onParentResize(_size));
+      for (final child in children) {
+        child.onParentResize(_size);
+      }
     }
   }
 

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

@@ -168,7 +168,7 @@ class TextBoxComponent<T extends TextRenderer> extends TextComponent {
     lines.clear();
     var lineHeight = 0.0;
     final maxBoxWidth = _fixedSize ? width : _boxConfig.maxWidth;
-    text.split(' ').forEach((word) {
+    for (final word in text.split(' ')) {
       final wordLines = word.split('\n');
       final possibleLine =
           lines.isEmpty ? wordLines[0] : '${lines.last} ${wordLines[0]}';
@@ -192,7 +192,7 @@ class TextBoxComponent<T extends TextRenderer> extends TextComponent {
       } else {
         lines.addAll(wordLines);
       }
-    });
+    }
     _totalLines = lines.length;
     _lineHeight = lineHeight;
     size = _recomputeSize();

packages/flame/lib/src/events/flame_game_mixins/double_tap_dispatcher.dart

@@ -36,12 +36,16 @@ class DoubleTapDispatcher extends Component with HasGameReference<FlameGame> {
   }
 
   void _onDoubleTapUp(DoubleTapEvent event) {
-    _components.forEach((component) => component.onDoubleTapUp(event));
+    for (final component in _components) {
+      component.onDoubleTapUp(event);
+    }
     _components.clear();
   }
 
   void _onDoubleTapCancel(DoubleTapCancelEvent event) {
-    _components.forEach((component) => component.onDoubleTapCancel(event));
+    for (final component in _components) {
+      component.onDoubleTapCancel(event);
+    }
     _components.clear();
   }
 

packages/flame/lib/src/experimental/geometry/shapes/polygon.dart

@@ -65,7 +65,7 @@ class Polygon extends Shape {
     var nInteriorAngles = 0;
     var nExteriorAngles = 0;
     var previousEdge = _edges.last;
-    _edges.forEach((edge) {
+    for (final edge in _edges) {
       final crossProduct = edge.cross(previousEdge);
       previousEdge = edge;
       // A straight angle counts as both internal and external
@@ -75,7 +75,7 @@ class Polygon extends Shape {
       if (crossProduct <= 0) {
         nExteriorAngles++;
       }
-    });
+    }
     if (nInteriorAngles < nExteriorAngles) {
       _reverseVertices();
       _initializeEdges();
@@ -116,7 +116,9 @@ class Polygon extends Shape {
   Aabb2? _aabb;
   Aabb2 _calculateAabb() {
     final aabb = Aabb2.minMax(_vertices.first, _vertices.first);
-    _vertices.forEach(aabb.hullPoint);
+    for (final vertex in _vertices) {
+      aabb.hullPoint(vertex);
+    }
     return aabb;
   }
 

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

@@ -186,7 +186,9 @@ class FlameGame<W extends World> extends ComponentTreeRoot
     // there is no way to explicitly call the [Component]'s implementation,
     // we propagate the event to [FlameGame]'s children manually.
     handleResize(size);
-    children.forEach((child) => child.onParentResize(size));
+    for (final child in children) {
+      child.onParentResize(size);
+    }
   }
 
   /// Ensure that all pending tree operations finish.

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

@@ -48,7 +48,9 @@ class LineSegment {
       };
       if (overlaps.isNotEmpty) {
         final sum = Vector2.zero();
-        overlaps.forEach(sum.add);
+        for (final overlap in overlaps) {
+          sum.add(overlap);
+        }
         return [sum..scale(1 / overlaps.length)];
       }
     }

packages/flame/lib/src/layers/layer.dart

@@ -14,16 +14,21 @@ abstract class Layer {
 
   @mustCallSuper
   void render(Canvas canvas, {double x = 0.0, double y = 0.0}) {
-    if (_picture == null) {
+    final picture = _picture;
+    if (picture == null) {
       return;
     }
 
     canvas.save();
     canvas.translate(x, y);
 
-    preProcessors.forEach((p) => p.process(_picture!, canvas));
-    canvas.drawPicture(_picture!);
-    postProcessors.forEach((p) => p.process(_picture!, canvas));
+    for (final p in preProcessors) {
+      p.process(picture, canvas);
+    }
+    canvas.drawPicture(picture);
+    for (final p in postProcessors) {
+      p.process(picture, canvas);
+    }
     canvas.restore();
   }
 

packages/flame/lib/src/parallax.dart

@@ -468,15 +468,15 @@ class Parallax {
   final _delta = Vector2.zero();
 
   void update(double dt) {
-    layers.forEach((layer) {
+    for (final layer in layers) {
       layer.update(
         _delta
           ..setFrom(baseVelocity)
           ..multiply(layer.velocityMultiplier)
           ..scale(dt),
         dt,
       );
-    });
+    }
   }
 
   /// Note that this method only should be used if all of your layers should

packages/flame/lib/src/text/elements/group_element.dart

@@ -12,12 +12,16 @@ class GroupElement extends BlockElement {
 
   @override
   void translate(double dx, double dy) {
-    children.forEach((child) => child.translate(dx, dy));
+    for (final child in children) {
+      child.translate(dx, dy);
+    }
   }
 
   @override
   void draw(Canvas canvas) {
-    children.forEach((child) => child.draw(canvas));
+    for (final child in children) {
+      child.draw(canvas);
+    }
   }
 
   @override