feat: implement collision skin

src/geometry/collider.rs

@@ -9,7 +9,7 @@ use crate::parry::transformation::vhacd::VHACDParameters;
 use crate::pipeline::{ActiveEvents, ActiveHooks};
 use crate::prelude::ColliderEnabled;
 use na::Unit;
-use parry::bounding_volume::Aabb;
+use parry::bounding_volume::{Aabb, BoundingVolume};
 use parry::shape::{Shape, TriMeshFlags};
 
 #[cfg(feature = "dim3")]
@@ -30,6 +30,7 @@ pub struct Collider {
     pub(crate) material: ColliderMaterial,
     pub(crate) flags: ColliderFlags,
     pub(crate) bf_data: ColliderBroadPhaseData,
+    collision_skin: Real,
     contact_force_event_threshold: Real,
     /// User-defined data associated to this collider.
     pub user_data: u128,
@@ -109,6 +110,7 @@ impl Collider {
             bf_data: _bf_data, // Internal ids must not be overwritten.
             contact_force_event_threshold,
             user_data,
+            collision_skin,
         } = other;
 
         if self.parent.is_none() {
@@ -123,6 +125,7 @@ impl Collider {
         self.user_data = *user_data;
         self.flags = *flags;
         self.changes = ColliderChanges::all();
+        self.collision_skin = *collision_skin;
     }
 
     /// The physics hooks enabled for this collider.
@@ -155,6 +158,16 @@ impl Collider {
         self.flags.active_collision_types = active_collision_types;
     }
 
+    /// The collision skin of this collider.
+    pub fn collision_skin(&self) -> Real {
+        self.collision_skin
+    }
+
+    /// Sets the collision skin of this collider.
+    pub fn set_collision_skin(&mut self, skin_thickness: Real) {
+        self.collision_skin = skin_thickness;
+    }
+
     /// The friction coefficient of this collider.
     pub fn friction(&self) -> Real {
         self.material.friction
@@ -437,10 +450,21 @@ impl Collider {
     }
 
     /// Compute the axis-aligned bounding box of this collider.
+    ///
+    /// This AABB doesn’t take into account the collider’s collision skin.
+    /// [`Collider::collision_skin`].
     pub fn compute_aabb(&self) -> Aabb {
         self.shape.compute_aabb(&self.pos)
     }
 
+    /// Compute the axis-aligned bounding box of this collider, taking into account the
+    /// [`Collider::collision_skin`] and prediction distance.
+    pub fn compute_collision_aabb(&self, prediction: Real) -> Aabb {
+        self.shape
+            .compute_aabb(&self.pos)
+            .loosened(self.collision_skin + prediction)
+    }
+
     /// Compute the axis-aligned bounding box of this collider moving from its current position
     /// to the given `next_position`
     pub fn compute_swept_aabb(&self, next_position: &Isometry<Real>) -> Aabb {
@@ -495,6 +519,8 @@ pub struct ColliderBuilder {
     pub enabled: bool,
     /// The total force magnitude beyond which a contact force event can be emitted.
     pub contact_force_event_threshold: Real,
+    /// An extract thickness around the collider shape to keep them further apart when in collision.
+    pub collision_skin: Real,
 }
 
 impl ColliderBuilder {
@@ -517,6 +543,7 @@ impl ColliderBuilder {
             active_events: ActiveEvents::empty(),
             enabled: true,
             contact_force_event_threshold: 0.0,
+            collision_skin: 0.0,
         }
     }
 
@@ -946,6 +973,20 @@ impl ColliderBuilder {
         self
     }
 
+    /// Sets the collision skin of the collider.
+    ///
+    /// The collision skin acts as if the collider was enlarged with a skin of width `skin_thickness`
+    /// around it, keeping objects further apart when colliding.
+    ///
+    /// A non-zero collision skin can increase performance, and in some cases, stability. However
+    /// it creates a small gap between colliding object (equal to the sum of their skin). If the
+    /// skin is sufficiently small, this might not be visually significant or can be hidden by the
+    /// rendering assets.
+    pub fn collision_skin(mut self, skin_thickness: Real) -> Self {
+        self.collision_skin = skin_thickness;
+        self
+    }
+
     /// Enable or disable the collider after its creation.
     pub fn enabled(mut self, enabled: bool) -> Self {
         self.enabled = enabled;
@@ -993,6 +1034,7 @@ impl ColliderBuilder {
             flags,
             coll_type,
             contact_force_event_threshold: self.contact_force_event_threshold,
+            collision_skin: self.collision_skin,
             user_data: self.user_data,
         }
     }