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https://github.com/bevyengine/bevy
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# Objective It is often necessary to update an entity's parent while keeping its GlobalTransform static. Currently it is cumbersome and error-prone (two questions in the discord `#help` channel in the past week) - Part 2, resolves #5475 - Builds on: #7020. ## Solution - Added the `BuildChildrenTransformExt` trait, it is part of `bevy::prelude` and adds the following methods to `EntityCommands`: - `set_parent_in_place`: Change the parent of an entity and update its `Transform` in order to preserve its `GlobalTransform` after the parent change - `remove_parent_in_place`: Remove an entity from a hierarchy, while preserving its `GlobalTransform`. --- ## Changelog - Added the `BuildChildrenTransformExt` trait, it is part of `bevy::prelude` and adds the following methods to `EntityCommands`: - `set_parent_in_place`: Change the parent of an entity and update its `Transform` in order to preserve its `GlobalTransform` after the parent change - `remove_parent_in_place`: Remove an entity from a hierarchy, while preserving its `GlobalTransform`. Co-authored-by: Nicola Papale <nicopap@users.noreply.github.com>
101 lines
4 KiB
Rust
101 lines
4 KiB
Rust
//! Extension to [`EntityCommands`] to modify [`bevy_hierarchy`] hierarchies
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//! while preserving [`GlobalTransform`].
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use bevy_ecs::{prelude::Entity, system::Command, system::EntityCommands, world::World};
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use bevy_hierarchy::{AddChild, RemoveParent};
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#[cfg(doc)]
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use bevy_hierarchy::BuildChildren;
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use crate::{GlobalTransform, Transform};
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/// Command similar to [`AddChild`], but updating the child transform to keep
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/// it at the same [`GlobalTransform`].
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///
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/// You most likely want to use [`BuildChildrenTransformExt::set_parent_in_place`]
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/// method on [`EntityCommands`] instead.
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pub struct AddChildInPlace {
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/// Parent entity to add the child to.
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pub parent: Entity,
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/// Child entity to add.
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pub child: Entity,
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}
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impl Command for AddChildInPlace {
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fn write(self, world: &mut World) {
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let hierarchy_command = AddChild {
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child: self.child,
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parent: self.parent,
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};
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hierarchy_command.write(world);
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// FIXME: Replace this closure with a `try` block. See: https://github.com/rust-lang/rust/issues/31436.
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let mut update_transform = || {
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let parent = *world.get_entity(self.parent)?.get::<GlobalTransform>()?;
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let child_global = *world.get_entity(self.child)?.get::<GlobalTransform>()?;
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let mut child_entity = world.get_entity_mut(self.child)?;
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let mut child = child_entity.get_mut::<Transform>()?;
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*child = child_global.reparented_to(&parent);
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Some(())
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};
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update_transform();
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}
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}
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/// Command similar to [`RemoveParent`], but updating the child transform to keep
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/// it at the same [`GlobalTransform`].
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///
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/// You most likely want to use [`BuildChildrenTransformExt::remove_parent_in_place`]
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/// method on [`EntityCommands`] instead.
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pub struct RemoveParentInPlace {
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/// `Entity` whose parent must be removed.
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pub child: Entity,
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}
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impl Command for RemoveParentInPlace {
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fn write(self, world: &mut World) {
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let hierarchy_command = RemoveParent { child: self.child };
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hierarchy_command.write(world);
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// FIXME: Replace this closure with a `try` block. See: https://github.com/rust-lang/rust/issues/31436.
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let mut update_transform = || {
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let child_global = *world.get_entity(self.child)?.get::<GlobalTransform>()?;
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let mut child_entity = world.get_entity_mut(self.child)?;
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let mut child = child_entity.get_mut::<Transform>()?;
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*child = child_global.compute_transform();
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Some(())
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};
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update_transform();
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}
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}
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/// Collection of methods similar to [`BuildChildren`], but preserving each
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/// entity's [`GlobalTransform`].
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pub trait BuildChildrenTransformExt {
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/// Change this entity's parent while preserving this entity's [`GlobalTransform`]
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/// by updating its [`Transform`].
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///
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/// See [`BuildChildren::set_parent`] for a method that doesn't update the
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/// [`Transform`].
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///
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/// Note that both the hierarchy and transform updates will only execute
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/// at the end of the current stage.
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fn set_parent_in_place(&mut self, parent: Entity) -> &mut Self;
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/// Make this entity parentless while preserving this entity's [`GlobalTransform`]
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/// by updating its [`Transform`] to be equal to its current [`GlobalTransform`].
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///
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/// See [`BuildChildren::remove_parent`] for a method that doesn't update the
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/// [`Transform`].
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///
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/// Note that both the hierarchy and transform updates will only execute
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/// at the end of the current stage.
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fn remove_parent_in_place(&mut self) -> &mut Self;
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}
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impl<'w, 's, 'a> BuildChildrenTransformExt for EntityCommands<'w, 's, 'a> {
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fn remove_parent_in_place(&mut self) -> &mut Self {
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let child = self.id();
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self.commands().add(RemoveParentInPlace { child });
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self
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}
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fn set_parent_in_place(&mut self, parent: Entity) -> &mut Self {
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let child = self.id();
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self.commands().add(AddChildInPlace { child, parent });
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self
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}
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}
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