Add solver flags for controlling whether or not some contacts should be taken into account by the constraints solver.

src/geometry/collider.rs

@@ -204,6 +204,7 @@ pub struct Collider {
     /// The restitution coefficient of this collider.
     pub restitution: f32,
     pub(crate) collision_groups: InteractionGroups,
+    pub(crate) solver_groups: InteractionGroups,
     pub(crate) contact_graph_index: ColliderGraphIndex,
     pub(crate) proximity_graph_index: ColliderGraphIndex,
     pub(crate) proxy_index: usize,
@@ -261,6 +262,11 @@ impl Collider {
         self.collision_groups
     }
 
+    /// The solver groups used by this collider.
+    pub fn solver_groups(&self) -> InteractionGroups {
+        self.solver_groups
+    }
+
     /// The density of this collider.
     pub fn density(&self) -> f32 {
         self.density
@@ -304,10 +310,12 @@ pub struct ColliderBuilder {
     pub delta: Isometry<f32>,
     /// Is this collider a sensor?
     pub is_sensor: bool,
-    /// The user-data of the collider beind built.
+    /// The user-data of the collider being built.
     pub user_data: u128,
     /// The collision groups for the collider being built.
     pub collision_groups: InteractionGroups,
+    /// The solver groups for the collider being built.
+    pub solver_groups: InteractionGroups,
 }
 
 impl ColliderBuilder {
@@ -322,6 +330,7 @@ impl ColliderBuilder {
             is_sensor: false,
             user_data: 0,
             collision_groups: InteractionGroups::all(),
+            solver_groups: InteractionGroups::all(),
         }
     }
 
@@ -442,6 +451,15 @@ impl ColliderBuilder {
         self
     }
 
+    /// Sets the solver groups used by this collider.
+    ///
+    /// Forces between two colliders in contact will be computed iff their solver groups are
+    /// compatible. See [InteractionGroups::test] for details.
+    pub fn solver_groups(mut self, groups: InteractionGroups) -> Self {
+        self.solver_groups = groups;
+        self
+    }
+
     /// Sets whether or not the collider built by this builder is a sensor.
     pub fn sensor(mut self, is_sensor: bool) -> Self {
         self.is_sensor = is_sensor;
@@ -523,6 +541,8 @@ impl ColliderBuilder {
             contact_graph_index: InteractionGraph::<Contact>::invalid_graph_index(),
             proximity_graph_index: InteractionGraph::<Proximity>::invalid_graph_index(),
             proxy_index: crate::INVALID_USIZE,
+            collision_groups: self.collision_groups,
+            solver_groups: self.solver_groups,
             user_data: self.user_data,
         }
     }