Trait EventHandler 

pub trait EventHandler: Send + Sync {
    // Required methods
    fn handle_collision_event(
        &self,
        bodies: &RigidBodySet,
        colliders: &ColliderSet,
        event: CollisionEvent,
        contact_pair: Option<&ContactPair>,
    );
    fn handle_contact_force_event(
        &self,
        dt: f32,
        bodies: &RigidBodySet,
        colliders: &ColliderSet,
        contact_pair: &ContactPair,
        total_force_magnitude: f32,
    );
}

A callback interface for receiving physics events (collisions starting/stopping, contact forces).

Implement this trait to get notified when:

• Two colliders start or stop touching (handle_collision_event)
• Contact forces exceed a threshold (handle_contact_force_event)

Common use cases

• Playing sound effects when objects collide
• Triggering game events (damage, pickups, checkpoints)
• Monitoring structural stress
• Detecting when specific objects touch

Built-in implementation

Use ChannelEventCollector to collect events into channels for processing after the physics step.

Example

struct MyEventHandler;

impl EventHandler for MyEventHandler {
    fn handle_collision_event(
        &self,
        bodies: &RigidBodySet,
        colliders: &ColliderSet,
        event: CollisionEvent,
        contact_pair: Option<&ContactPair>,
    ) {
        match event {
            CollisionEvent::Started(h1, h2, _) => {
                println!("Collision started between {:?} and {:?}", h1, h2);
            }
            CollisionEvent::Stopped(h1, h2, _) => {
                println!("Collision ended between {:?} and {:?}", h1, h2);
            }
        }
    }
}

Required Methods

fn handle_collision_event( &self, bodies: &RigidBodySet, colliders: &ColliderSet, event: CollisionEvent, contact_pair: Option<&ContactPair>, )

Called when two colliders start or stop touching each other.

Collision events are triggered when intersection state changes (Started/Stopped). At least one collider must have ActiveEvents::COLLISION_EVENTS enabled.

Parameters

• event - Either Started(h1, h2, flags) or Stopped(h1, h2, flags)
• bodies - All rigid bodies (to look up body info)
• colliders - All colliders (to look up collider info)
• contact_pair - Detailed contact info (None for sensors, since they don’t compute contacts)

Use cases

• Play collision sound effects
• Apply damage when objects hit
• Trigger game events (entering zones, picking up items)
• Track what’s touching what

fn handle_contact_force_event( &self, dt: f32, bodies: &RigidBodySet, colliders: &ColliderSet, contact_pair: &ContactPair, total_force_magnitude: f32, )

Called when contact forces exceed a threshold.

Triggered when the total force magnitude between two colliders exceeds the Collider::contact_force_event_threshold. At least one collider must have ActiveEvents::CONTACT_FORCE_EVENTS enabled.

Use cases

• Detect hard impacts (for damage, breaking objects)
• Monitor structural stress
• Trigger effects at certain force levels (sparks, cracks)

Parameters

• total_force_magnitude - Sum of magnitudes of all contact forces (not vector sum!) Example: Two forces [0, 100, 0] and [0, -100, 0] → magnitude = 200 (not 0)

Implementations on Foreign Types

impl EventHandler for ()

fn handle_collision_event( &self, _bodies: &RigidBodySet, _colliders: &ColliderSet, _event: CollisionEvent, _contact_pair: Option<&ContactPair>, )

fn handle_contact_force_event( &self, _dt: f32, _bodies: &RigidBodySet, _colliders: &ColliderSet, _contact_pair: &ContactPair, _total_force_magnitude: f32, )

Implementors

impl EventHandler for ChannelEventCollector