Is there a way of detecting collision of Sprites in the bevy game engine?

Question

Currently im using the Position of two objects (comets and the ship) to detect if they collide.

fn collision_detection(
    comets: Query<&Transform, With<Comet>>,
    mut ships: Query<(&Transform, &mut ShipStatus), With<Ship>>,
) {
    for comet in comets.iter() {
        for (ship, mut status) in ships.iter_mut() {
            if comet.translation.x < ship.translation.x + 80.0 && comet.translation.y < ship.translation.y + 80.0
            && comet.translation.x > ship.translation.x - 80.0 && comet.translation.y > ship.translation.y - 80.0 {
                status.dead = true;
            }
        }
    }
}

But there has to be a better way of doing this.

Araxes

Answer 1

Bevy doesn't have a complete collision system currently. Unless it has been expanded in the few months since the introductory page was created:

Physics

Many games require collision detection and physics. I'm planning on building a plug-able physics interface with nphysics / ncollide as the first backend.

Fortunately, this simple example is actually provided by bevy::sprite::collide_aabb::collide which does simple AABB collision detection.

use bevy::sprite::collide_aabb::collide;

let ship_size = Vec2::new(80.0, 80.0);
let comet_size = Vec2::new(0.0, 0.0);
for comet in comets.iter() {
    for (ship, mut status) in ships.iter_mut() {
        if collide(ship.translation, ship_size, comet.translation, comet_size).is_some() {
            status.dead = true;
        }
    }
}

Pathy

Hi, cool answer! Is there a faster approach? currently it seems this should work in O(n*m), while there are data structures that allow faster collision detection, such as R-trees and the other structures derived from it. However, I struggle to see how this would be implemented in a bevy system that gets a simple iterator over the ships and comets... – Somatoplasm

Answer 2

There's https://lib.rs/crates/bevy_spatial with KD-Tree nowadays.

Usage example from the info page:

use bevy_spatial::{AutomaticUpdate, KDTree3, TransformMode, SpatialAccess};

#[derive(Component, Default)]
struct TrackedByKDTree;

fn main() {
    App::new()
        .add_plugin(AutomaticUpdate::<TrackedByKDTree>::new()
            .with_frequency(Duration::from_secs_f32(0.3))
            .with_transform(TransformMode::GlobalTransform))
        .add_systems(Update, use_neighbour);
    // ...
}

type NNTree = KDTree3<TrackedByKDTree>; // type alias for later

// spawn some entities with the TrackedByKDTree component

fn use_neighbour(tree: Res<NNTree>){
    if let Some((pos, entity)) = tree.nearest_neighbour(Vec3::ZERO) {
        // pos: Vec3
        // do something with the nearest entity here
    }
}

Tranquilizer