Struct bevy::ecs::query::Changed

pub struct Changed<T>(_);

A filter on a component that only retains results added or mutably dereferenced after the system last ran.

A common use for this filter is avoiding redundant work when values have not changed.

Note that simply mutably dereferencing a component is considered a change (DerefMut). Bevy does not compare components to their previous values.

To retain all results without filtering but still check whether they were changed after the system last ran, use ChangeTrackers<T>.

Examples

fn print_moving_objects_system(query: Query<&Name, Changed<Transform>>) {
    for name in &query {
        println!("Entity Moved: {:?}", name);
    }
}

Trait Implementations

impl<T> WorldQuery for Changed<T> where
    T: Component, 

type ReadOnly = Changed<T>

type State = ChangedState<T>

fn shrink<'wlong, 'wshort>(
    item: <<Changed<T> as WorldQueryGats<'wlong>>::Fetch as Fetch<'wlong>>::Item
) -> <<Changed<T> as WorldQueryGats<'wshort>>::Fetch as Fetch<'wshort>>::Item where
    'wlong: 'wshort, 

This function manually implements variance for the query items.

impl<'w, T> WorldQueryGats<'w> for Changed<T> where
    T: Component, 

type Fetch = ChangedFetch<'w, T>

type _State = ChangedState<T>

impl<T> ReadOnlyWorldQuery for Changed<T> where
    T: Component, 

SAFETY: read-only access