implemented patch by Vroonsh to optimize island management with many static objects.

It can be disabled by commenting out the #define STATIC_SIMULATION_ISLAND_OPTIMIZATION in Bullet/src/BulletCollision/CollisionDispatch/btUnionFind.h

See also Issue 406

src/BulletCollision/CollisionDispatch/btSimulationIslandManager.cpp

@@ -1,3 +1,4 @@
+
 /*
 Bullet Continuous Collision Detection and Physics Library
 Copyright (c) 2003-2006 Erwin Coumans  http://continuousphysics.com/Bullet/
@@ -65,15 +66,69 @@ void btSimulationIslandManager::findUnions(btDispatcher* /* dispatcher */,btColl
 	}
 }
 
+#ifdef STATIC_SIMULATION_ISLAND_OPTIMIZATION
+void   btSimulationIslandManager::updateActivationState(btCollisionWorld* colWorld,btDispatcher* dispatcher)
+{
 
+	// put the index into m_controllers into m_tag   
+	int index = 0;
+	{
+
+		int i;
+		for (i=0;i<colWorld->getCollisionObjectArray().size(); i++)
+		{
+			btCollisionObject*   collisionObject= colWorld->getCollisionObjectArray()[i];
+			//Adding filtering here
+			if (!collisionObject->isStaticOrKinematicObject())
+			{
+				collisionObject->setIslandTag(index++);
+			}
+			collisionObject->setCompanionId(-1);
+			collisionObject->setHitFraction(btScalar(1.));
+		}
+	}
+	// do the union find
+
+	initUnionFind( index );
+
+	findUnions(dispatcher,colWorld);
+}
+
+void   btSimulationIslandManager::storeIslandActivationState(btCollisionWorld* colWorld)
+{
+	// put the islandId ('find' value) into m_tag   
+	{
+		int index = 0;
+		int i;
+		for (i=0;i<colWorld->getCollisionObjectArray().size();i++)
+		{
+			btCollisionObject* collisionObject= colWorld->getCollisionObjectArray()[i];
+			if (!collisionObject->isStaticOrKinematicObject())
+			{
+				collisionObject->setIslandTag( m_unionFind.find(index) );
+				//Set the correct object offset in Collision Object Array
+				m_unionFind.getElement(index).m_sz = i;
+				collisionObject->setCompanionId(-1);
+				index++;
+			} else
+			{
+				collisionObject->setIslandTag(-1);
+				collisionObject->setCompanionId(-2);
+			}
+		}
+	}
+}
+
+
+#else //STATIC_SIMULATION_ISLAND_OPTIMIZATION
 void	btSimulationIslandManager::updateActivationState(btCollisionWorld* colWorld,btDispatcher* dispatcher)
 {
-	
+
 	initUnionFind( int (colWorld->getCollisionObjectArray().size()));
-	
+
 	// put the index into m_controllers into m_tag	
 	{
-		
+
 		int index = 0;
 		int i;
 		for (i=0;i<colWorld->getCollisionObjectArray().size(); i++)
@@ -83,26 +138,20 @@ void	btSimulationIslandManager::updateActivationState(btCollisionWorld* colWorld
 			collisionObject->setCompanionId(-1);
 			collisionObject->setHitFraction(btScalar(1.));
 			index++;
-			
+
 		}
 	}
 	// do the union find
-	
+
 	findUnions(dispatcher,colWorld);
-	
-
-	
 }
 
-
-
-
 void	btSimulationIslandManager::storeIslandActivationState(btCollisionWorld* colWorld)
 {
 	// put the islandId ('find' value) into m_tag	
 	{
-		
+
-		
+
 		int index = 0;
 		int i;
 		for (i=0;i<colWorld->getCollisionObjectArray().size();i++)
@@ -122,6 +171,8 @@ void	btSimulationIslandManager::storeIslandActivationState(btCollisionWorld* col
 	}
 }
 
+#endif //STATIC_SIMULATION_ISLAND_OPTIMIZATION
+
 inline	int	getIslandId(const btPersistentManifold* lhs)
 {
 	int islandId;

src/BulletCollision/CollisionDispatch/btUnionFind.cpp

@@ -70,7 +70,9 @@ void	btUnionFind::sortIslands()
 	for (int i=0;i<numElements;i++)
 	{
 		m_elements[i].m_id = find(i);
+#ifndef STATIC_SIMULATION_ISLAND_OPTIMIZATION
 		m_elements[i].m_sz = i;
+#endif //STATIC_SIMULATION_ISLAND_OPTIMIZATION
 	}
 	
 	 // Sort the vector using predicate and std::sort
@@ -78,4 +80,3 @@ void	btUnionFind::sortIslands()
 	  m_elements.quickSort(btUnionFindElementSortPredicate());
 
 }
-

src/BulletCollision/CollisionDispatch/btUnionFind.h

@@ -18,7 +18,10 @@ subject to the following restrictions:
 
 #include "LinearMath/btAlignedObjectArray.h"
 
-	#define USE_PATH_COMPRESSION 1
+#define USE_PATH_COMPRESSION 1
+
+///see for discussion of static island optimizations by Vroonsh here: http://code.google.com/p/bullet/issues/detail?id=406
+#define STATIC_SIMULATION_ISLAND_OPTIMIZATION 1
 
 struct	btElement
 {