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

src/geometry/contact.rs

@@ -9,6 +9,16 @@ use {
     simba::simd::SimdValue,
 };
 
+bitflags::bitflags! {
+    #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+    /// Flags affecting the behavior of the constraints solver for a given contact manifold.
+    pub struct SolverFlags: u32 {
+        /// The constraint solver will take this contact manifold into
+        /// account for force computation.
+        const COMPUTE_FORCES = 0b01;
+    }
+}
+
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
 /// The type local linear approximation of the neighborhood of a pair contact points on two shapes
@@ -206,6 +216,7 @@ impl ContactPair {
     pub(crate) fn single_manifold<'a, 'b>(
         &'a mut self,
         colliders: &'b ColliderSet,
+        flags: SolverFlags,
     ) -> (
         &'b Collider,
         &'b Collider,
@@ -216,7 +227,7 @@ impl ContactPair {
         let coll2 = &colliders[self.pair.collider2];
 
         if self.manifolds.len() == 0 {
-            let manifold = ContactManifold::from_colliders(self.pair, coll1, coll2);
+            let manifold = ContactManifold::from_colliders(self.pair, coll1, coll2, flags);
             self.manifolds.push(manifold);
         }
 
@@ -288,6 +299,8 @@ pub struct ContactManifold {
     /// The relative position between the second collider and its parent at the time the
     /// contact points were generated.
     pub delta2: Isometry<f32>,
+    /// Flags used to control some aspects of the constraints solver for this contact manifold.
+    pub solver_flags: SolverFlags,
 }
 
 impl ContactManifold {
@@ -299,6 +312,7 @@ impl ContactManifold {
         delta2: Isometry<f32>,
         friction: f32,
         restitution: f32,
+        solver_flags: SolverFlags,
     ) -> ContactManifold {
         Self {
             #[cfg(feature = "dim2")]
@@ -319,6 +333,7 @@ impl ContactManifold {
             delta2,
             constraint_index: 0,
             position_constraint_index: 0,
+            solver_flags,
         }
     }
 
@@ -342,11 +357,17 @@ impl ContactManifold {
             delta2: self.delta2,
             constraint_index: self.constraint_index,
             position_constraint_index: self.position_constraint_index,
+            solver_flags: self.solver_flags,
         }
     }
 
-    pub(crate) fn from_colliders(pair: ColliderPair, coll1: &Collider, coll2: &Collider) -> Self {
-        Self::with_subshape_indices(pair, coll1, coll2, 0, 0)
+    pub(crate) fn from_colliders(
+        pair: ColliderPair,
+        coll1: &Collider,
+        coll2: &Collider,
+        flags: SolverFlags,
+    ) -> Self {
+        Self::with_subshape_indices(pair, coll1, coll2, 0, 0, flags)
     }
 
     pub(crate) fn with_subshape_indices(
@@ -355,6 +376,7 @@ impl ContactManifold {
         coll2: &Collider,
         subshape1: usize,
         subshape2: usize,
+        solver_flags: SolverFlags,
     ) -> Self {
         Self::new(
             pair,
@@ -364,6 +386,7 @@ impl ContactManifold {
             *coll2.position_wrt_parent(),
             (coll1.friction + coll2.friction) * 0.5,
             (coll1.restitution + coll2.restitution) * 0.5,
+            solver_flags,
         )
     }