+ make compound versus soft body work (soft body uses interpolated transform)

+ fixed issue with persistent manifold, warmstarting values were not initialized properly
+ don't clear manifold in sphere-sphere collision (need warmstarting)
+ added support for 'split impulse', decouple positional error correction from velocity correction
This avoids adding momentum due to penetration correction, it can be tuned using following variables:
solverInfo.m_splitImpulse = true/false (disable/enable)
solverInfo.m_splitImpulsePenetrationThreshold (below this value, baumgarte/mixed velocity/penetration is used (cheaper, looks more plausible)
solverInfo.m_linearSlop (less jitter, when small amound of penetration is allowed)

src/BulletCollision/CollisionDispatch/btCompoundCollisionAlgorithm.cpp

@@ -77,17 +77,22 @@ void btCompoundCollisionAlgorithm::processCollision (btCollisionObject* body0,bt
 
 		//backup
 		btTransform	orgTrans = colObj->getWorldTransform();
+		btTransform	orgInterpolationTrans = colObj->getInterpolationWorldTransform();
+
 		btCollisionShape* orgShape = colObj->getCollisionShape();
 
 		const btTransform& childTrans = compoundShape->getChildTransform(i);
-		//btTransform	newChildWorldTrans = orgTrans*childTrans ;
-		colObj->setWorldTransform( orgTrans*childTrans );
+		btTransform	newChildWorldTrans = orgTrans*childTrans ;
+		colObj->setWorldTransform( newChildWorldTrans);
+		colObj->setInterpolationWorldTransform(newChildWorldTrans);
+
 		//the contactpoint is still projected back using the original inverted worldtrans
 		colObj->setCollisionShape( childShape );
 		m_childCollisionAlgorithms[i]->processCollision(colObj,otherObj,dispatchInfo,resultOut);
 		//revert back
 		colObj->setCollisionShape( orgShape);
 		colObj->setWorldTransform(  orgTrans );
+		colObj->setInterpolationWorldTransform(orgInterpolationTrans);
 	}
 }
 

src/BulletCollision/CollisionDispatch/btSphereSphereCollisionAlgorithm.cpp

@@ -56,7 +56,7 @@ void btSphereSphereCollisionAlgorithm::processCollision (btCollisionObject* col0
 	btScalar radius0 = sphere0->getRadius();
 	btScalar radius1 = sphere1->getRadius();
 
-	m_manifoldPtr->clearManifold();
+	//m_manifoldPtr->clearManifold(); //don't do this, it disables warmstarting
 
 	///iff distance positive, don't generate a new contact
 	if ( len > (radius0+radius1))