Struct bevy::ecs::query::QueryParIter

pub struct QueryParIter<'w, 's, D, F>
where
    D: QueryData,
    F: QueryFilter,
{ /* private fields */ }

A parallel iterator over query results of a Query.

This struct is created by the Query::par_iter and Query::par_iter_mut methods.

Implementations

impl<'w, 's, D, F> QueryParIter<'w, 's, D, F>

where D: QueryData, F: QueryFilter,

pub fn batching_strategy( self, strategy: BatchingStrategy ) -> QueryParIter<'w, 's, D, F>

Changes the batching strategy used when iterating.

For more information on how this affects the resultant iteration, see BatchingStrategy.

Examples found in repository

examples/ecs/parallel_query.rs (line 57)

fn bounce_system(windows: Query<&Window>, mut sprites: Query<(&Transform, &mut Velocity)>) {
    let window = windows.single();
    let width = window.width();
    let height = window.height();
    let left = width / -2.0;
    let right = width / 2.0;
    let bottom = height / -2.0;
    let top = height / 2.0;
    // The default batch size can also be overridden.
    // In this case a batch size of 32 is chosen to limit the overhead of
    // ParallelIterator, since negating a vector is very inexpensive.
    sprites
        .par_iter_mut()
        .batching_strategy(BatchingStrategy::fixed(32))
        .for_each(|(transform, mut v)| {
            if !(left < transform.translation.x
                && transform.translation.x < right
                && bottom < transform.translation.y
                && transform.translation.y < top)
            {
                // For simplicity, just reverse the velocity; don't use realistic bounces
                v.0 = -v.0;
            }
        });
}

pub fn for_each<FN>(self, func: FN)

where FN: Fn(<D as WorldQuery>::Item<'w>) + Send + Sync + Clone,

Runs func on each query result in parallel.

Panics

If the ComputeTaskPool is not initialized. If using this from a query that is being initialized and run from the ECS scheduler, this should never panic.

Examples found in repository

examples/ecs/parallel_query.rs (lines 38-40)

fn move_system(mut sprites: Query<(&mut Transform, &Velocity)>) {
    // Compute the new location of each sprite in parallel on the
    // ComputeTaskPool
    //
    // This example is only for demonstrative purposes. Using a
    // ParallelIterator for an inexpensive operation like addition on only 128
    // elements will not typically be faster than just using a normal Iterator.
    // See the ParallelIterator documentation for more information on when
    // to use or not use ParallelIterator over a normal Iterator.
    sprites
        .par_iter_mut()
        .for_each(|(mut transform, velocity)| {
            transform.translation += velocity.extend(0.0);
        });
}

// Bounce sprites outside the window
fn bounce_system(windows: Query<&Window>, mut sprites: Query<(&Transform, &mut Velocity)>) {
    let window = windows.single();
    let width = window.width();
    let height = window.height();
    let left = width / -2.0;
    let right = width / 2.0;
    let bottom = height / -2.0;
    let top = height / 2.0;
    // The default batch size can also be overridden.
    // In this case a batch size of 32 is chosen to limit the overhead of
    // ParallelIterator, since negating a vector is very inexpensive.
    sprites
        .par_iter_mut()
        .batching_strategy(BatchingStrategy::fixed(32))
        .for_each(|(transform, mut v)| {
            if !(left < transform.translation.x
                && transform.translation.x < right
                && bottom < transform.translation.y
                && transform.translation.y < top)
            {
                // For simplicity, just reverse the velocity; don't use realistic bounces
                v.0 = -v.0;
            }
        });
}