Fix child_builder and Parent / Children management

crates/bevy_transform/Cargo.toml

@@ -22,3 +22,10 @@ bevy_utils = { path = "../bevy_utils", version = "0.3.0" }
 
 # other
 smallvec = { version = "1.4", features = ["serde"] }
+
+[dev-dependencies]
+bencher = "0.1.5"
+
+[[bench]]
+name = "push_children"
+harness = false

crates/bevy_transform/benches/push_children.rs

@@ -0,0 +1,64 @@
+use bencher::*;
+
+use bevy_ecs::{Command, Commands, Component, DynamicBundle, Entity, Resources, World};
+use bevy_transform::prelude::*;
+
+fn push_children_1_parent_to_many_children(bench: &mut Bencher) {
+    let mut world = World::default();
+    let mut commands = Commands::default();
+    let mut resources = Resources::default();
+
+    let entities = world
+        .spawn_batch((0..1000).map(|i| (i,)))
+        .collect::<Vec<_>>();
+
+    bench.iter(|| {
+        commands.push_children(entities[999], &entities[0..998]);
+        commands.apply(&mut world, &mut resources);
+    })
+}
+
+fn push_children_many_parents_with_1_child(bench: &mut Bencher) {
+    let mut world = World::default();
+    let mut commands = Commands::default();
+    let mut resources = Resources::default();
+
+    let entities = world
+        .spawn_batch((0..2000).map(|i| (i,)))
+        .collect::<Vec<_>>();
+
+    bench.iter(|| {
+        for parent in 0..1000 {
+            let child = parent + 1000;
+            commands.push_children(entities[parent], &entities[child..=child]);
+        }
+        commands.apply(&mut world, &mut resources);
+    })
+}
+
+fn push_children_many_parents_with_8_children(bench: &mut Bencher) {
+    let mut world = World::default();
+    let mut commands = Commands::default();
+    let mut resources = Resources::default();
+
+    let entities = world
+        .spawn_batch((0..9000).map(|i| (i,)))
+        .collect::<Vec<_>>();
+
+    bench.iter(|| {
+        for parent in 0..1000 {
+            let child_a = parent * 8 + 1000;
+            let child_z = (parent + 1) * 8 + 1000;
+            commands.push_children(entities[parent], &entities[child_a..child_z]);
+        }
+        commands.apply(&mut world, &mut resources);
+    })
+}
+
+benchmark_group!(
+    benches,
+    push_children_1_parent_to_many_children,
+    push_children_many_parents_with_1_child,
+    push_children_many_parents_with_8_children
+);
+benchmark_main!(benches);

crates/bevy_transform/src/components/children.rs

@@ -3,7 +3,7 @@ use bevy_reflect::{Reflect, ReflectComponent, ReflectMapEntities};
 use smallvec::SmallVec;
 use std::ops::Deref;
 
-#[derive(Default, Clone, Debug, Reflect)]
+#[derive(Default, Clone, Debug, Reflect, Eq, PartialEq)]
 #[reflect(Component, MapEntities)]
 pub struct Children(pub(crate) SmallVec<[Entity; 8]>);