build islands once and process islands arbitrary number of times in update constraints

src/BulletCollision/CollisionDispatch/btSimulationIslandManager.cpp

@@ -338,13 +338,17 @@ void btSimulationIslandManager::buildIslands(btDispatcher* dispatcher, btCollisi
 	}
 }
 
+
 ///@todo: this is random access, it can be walked 'cache friendly'!
 void btSimulationIslandManager::buildAndProcessIslands(btDispatcher* dispatcher, btCollisionWorld* collisionWorld, IslandCallback* callback)
 {
-	btCollisionObjectArray& collisionObjects = collisionWorld->getCollisionObjectArray();
-
 	buildIslands(dispatcher, collisionWorld);
+    processIslands(dispatcher, collisionWorld, callback);
+}
 
+void btSimulationIslandManager::processIslands(btDispatcher* dispatcher, btCollisionWorld* collisionWorld, IslandCallback* callback)
+{
+    btCollisionObjectArray& collisionObjects = collisionWorld->getCollisionObjectArray();
 	int endIslandIndex = 1;
 	int startIslandIndex;
 	int numElem = getUnionFind().getNumElements();

src/BulletCollision/CollisionDispatch/btSimulationIslandManager.h

@@ -57,7 +57,7 @@ public:
 	};
 
 	void buildAndProcessIslands(btDispatcher* dispatcher, btCollisionWorld* collisionWorld, IslandCallback* callback);
-
+    void processIslands(btDispatcher* dispatcher, btCollisionWorld* collisionWorld, IslandCallback* callback);
 	void buildIslands(btDispatcher* dispatcher, btCollisionWorld* colWorld);
 
 	bool getSplitIslands()

src/BulletDynamics/Featherstone/btMultiBodyDynamicsWorld.cpp

@@ -428,13 +428,18 @@ void btMultiBodyDynamicsWorld::forwardKinematics()
 void btMultiBodyDynamicsWorld::solveConstraints(btContactSolverInfo& solverInfo)
 {
     solveExternalForces(solverInfo);
-    buildIslands();
+    m_islandManager->buildAndProcessIslands(getCollisionWorld()->getDispatcher(), getCollisionWorld(), m_solverMultiBodyIslandCallback);
     solveInternalConstraints(solverInfo);
 }
 
 void btMultiBodyDynamicsWorld::buildIslands()
 {
-    m_islandManager->buildAndProcessIslands(getCollisionWorld()->getDispatcher(), getCollisionWorld(), m_solverMultiBodyIslandCallback);
+    m_islandManager->buildIslands(getCollisionWorld()->getDispatcher(), getCollisionWorld());
+}
+
+void btMultiBodyDynamicsWorld::processIslands()
+{
+    m_islandManager->processIslands(getCollisionWorld()->getDispatcher(), getCollisionWorld(), m_solverMultiBodyIslandCallback);
 }
 
 void btMultiBodyDynamicsWorld::solveInternalConstraints(btContactSolverInfo& solverInfo)
@@ -1086,3 +1091,8 @@ void btMultiBodyDynamicsWorld::serializeMultiBodies(btSerializer* serializer)
 		}
 	}
 }
+
+void btMultiBodyDynamicsWorld::setSplitIslands(bool split)
+{
+    m_islandManager->setSplitIslands(split);
+}

src/BulletDynamics/Featherstone/btMultiBodyDynamicsWorld.h

@@ -118,6 +118,8 @@ public:
     virtual void solveExternalForces(btContactSolverInfo& solverInfo);
     virtual void solveInternalConstraints(btContactSolverInfo& solverInfo);
     void buildIslands();
+    void processIslands();
+    void setSplitIslands(bool split);
 
 };
 #endif  //BT_MULTIBODY_DYNAMICS_WORLD_H

src/BulletSoftBody/btDeformableBackwardEulerObjective.cpp

@@ -143,6 +143,8 @@ void btDeformableBackwardEulerObjective::setConstraints()
 {
     // build islands for multibody solve
     m_world->btMultiBodyDynamicsWorld::buildIslands();
+    // for repeated constraint solve, splitIslands has to be set to true
+    m_world->setSplitIslands(true);
     projection.setConstraints();
 }
 

src/BulletSoftBody/btDeformableBodySolver.cpp

@@ -19,7 +19,7 @@
 btDeformableBodySolver::btDeformableBodySolver()
 : m_numNodes(0)
 , m_cg(10)
-, m_contact_iterations(10)
+, m_contact_iterations(5)
 {
     m_objective = new btDeformableBackwardEulerObjective(m_softBodySet, m_backupVelocity);
 }

src/BulletSoftBody/btDeformableContactProjection.cpp

@@ -51,9 +51,11 @@ static btVector3 generateUnitOrthogonalVector(const btVector3& u)
 void btDeformableContactProjection::update()
 {
     ///solve rigid body constraints
-    m_world->getSolverInfo().m_numIterations = 1;
-    m_world->btMultiBodyDynamicsWorld::solveInternalConstraints(m_world->getSolverInfo());
-
+    {
+        m_world->getSolverInfo().m_numIterations = 1;
+        m_world->processIslands();
+        m_world->btMultiBodyDynamicsWorld::solveInternalConstraints(m_world->getSolverInfo()); // process constraints deferred in the previous step
+    }
     // loop through constraints to set constrained values
     for (int index = 0; index < m_constraints.size(); ++index)
     {