Add ActiveEvents::CONTACT_FORCE_EVENTS for consistency with ActiveEvents::COLLISION_EVENTS

CHANGELOG.md

@@ -22,6 +22,10 @@
 - Add `ColliderBuilder::mass` to set the mass of the collider instead of its density. Its angular
   inertia tensor will be automatically computed based on this mass and its shape.
 - Add `Collider::mass` and `Collider::volume` to retrieve the mass or volume of a collider.
+- Add the `ContactForceEvent` event. This event is useful to read contact forces. A `ContactForceEvent`
+  is generated whenever the sum of the magnitudes of the forces applied by contacts between two colliders
+  exceeds the value specified by `Collider::contact_force_event_threshold` on any of the two colliders with
+  the `ActiveEvents::CONTACT_FORCE_EVENT` flag set.
 
 ## v0.13.0 (31 May 2022)
 ### Fixed

src/geometry/collider.rs

@@ -26,7 +26,7 @@ pub struct Collider {
     pub(crate) material: ColliderMaterial,
     pub(crate) flags: ColliderFlags,
     pub(crate) bf_data: ColliderBroadPhaseData,
-    pub(crate) contact_force_event_threshold: Real,
+    contact_force_event_threshold: Real,
     /// User-defined data associated to this collider.
     pub user_data: u128,
 }
@@ -37,6 +37,14 @@ impl Collider {
         self.changes = ColliderChanges::all();
     }
 
+    pub(crate) fn effective_contact_force_event_threshold(&self) -> Real {
+        if self.flags.active_events.contains(ActiveEvents::CONTACT_FORCE_EVENTS) {
+            self.contact_force_event_threshold
+        } else {
+            Real::MAX
+        }
+    }
+
     /// The rigid body this collider is attached to.
     pub fn parent(&self) -> Option<RigidBodyHandle> {
         self.parent.map(|parent| parent.handle)
@@ -412,7 +420,7 @@ impl ColliderBuilder {
             active_collision_types: ActiveCollisionTypes::default(),
             active_hooks: ActiveHooks::empty(),
             active_events: ActiveEvents::empty(),
-            contact_force_event_threshold: Real::MAX,
+            contact_force_event_threshold: 0.0,
         }
     }
 

src/pipeline/event_handler.rs

@@ -7,9 +7,12 @@ bitflags::bitflags! {
     #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
     /// Flags affecting the events generated for this collider.
     pub struct ActiveEvents: u32 {
-        /// If set, Rapier will call `EventHandler::handle_contact_event`
+        /// If set, Rapier will call `EventHandler::handle_collision_event`
         /// whenever relevant for this collider.
         const COLLISION_EVENTS = 0b0001;
+        /// If set, Rapier will call `EventHandler::handle_contact_force_event`
+        /// whenever relevant for this collider.
+        const CONTACT_FORCE_EVENTS = 0b0010;
     }
 }
 
@@ -48,7 +51,7 @@ pub trait EventHandler: Send + Sync {
     ///
     /// A force event is generated whenever the total force magnitude applied between two
     /// colliders is `> Collider::contact_force_event_threshold` value of any of these
-    /// colliders.
+    /// colliders with the `ActiveEvents::CONTACT_FORCE_EVENTS` flag set.
     ///
     /// The "total force magnitude" here means "the sum of the magnitudes of the forces applied at
     /// all the contact points in a contact pair". Therefore, if the contact pair involves two

src/pipeline/physics_pipeline.rs

@@ -291,8 +291,8 @@ impl PhysicsPipeline {
             let co1 = &colliders[pair.collider1];
             let co2 = &colliders[pair.collider2];
             let threshold = co1
-                .contact_force_event_threshold
-                .min(co2.contact_force_event_threshold);
+                .effective_contact_force_event_threshold()
+                .min(co2.effective_contact_force_event_threshold());
 
             if threshold < Real::MAX {
                 let total_magnitude = pair.total_impulse_magnitude() * inv_dt;