Struct ScopeTree 

pub(crate) struct ScopeTree {
    parents: EntityHashMap<Entity>,
    children: EntityHashMap<Vec<Entity>>,
}

The parent and child links of every live entity.

Fields

parents: EntityHashMap<Entity>

children: EntityHashMap<Vec<Entity>>

Implementations

impl ScopeTree

pub(crate) fn attach(&mut self, entity: Entity, parent: Entity)

Record that entity lives in parent, dropping its old link.

pub(crate) fn detach(&mut self, entity: Entity)

Drop entity’s link to its parent, keeping its children linked to it.

pub(crate) fn parent(&self, entity: Entity) -> Result<Entity, EntityAccessError>

The parent of entity.

Every live entity is attached to the tree in the same step that gives it a row, so a handle missing from it names no live entity.

pub(crate) fn children(&self, entity: Entity) -> &[Entity]

The direct children of entity.

pub(crate) fn is_descendant(&self, ancestor: Entity, entity: Entity) -> bool

Whether entity is strictly below ancestor in the tree.

A walk up the parent chain rather than an interval comparison: the tree is as deep as a scene nests, which is a handful of levels, while an interval index would have to be rebuilt over the whole world on every spawn. The walk is bounded by the number of nodes so that a corrupted index cannot loop forever.

pub(crate) fn subtree_post_order(&self, root: Entity) -> Vec<Entity>

The subtree rooted at root, deepest first.

Post-order is what a cascade despawn needs: a child is removed before the parent it lived in, so a child’s callback still sees living ancestors.

Trait Implementations

impl Default for ScopeTree

fn default() -> Self

Returns the “default value” for a type.