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gContactAddedCallback = CustomMaterialCombinerCallback;

///this flag will use the friction information from the contact point, if contactPoint.m_lateralFrictionInitialized==true
m_dynamicsWorld->getSolverInfo().m_solverMode |= SOLVER_ENABLE_FRICTION_DIRECTION_CACHING;

///enable the callback for the ground object
body->setCollisionFlags(body->getCollisionFlags()  | btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK);

static bool CustomMaterialCombinerCallback(btManifoldPoint& cp,	const btCollisionObject* colObj0,int partId0,int index0,const btCollisionObject* colObj1,int partId1,int index1)
{
	cp.m_lateralFrictionInitialized = true;
	///choose a target velocity in the friction dir1 direction, for a conveyor belt effect
	cp.m_lateralFrictionDir1.setValue(0.5,0.5,0.5);
	cp.m_lateralFrictionDir1.normalize();

	///optionally downscale the friction direction 2 for lower (anisotropic) friction (rather than a unit vector)
	btScalar downscale = 1.f;
	cp.m_lateralFrictionDir2 = downscale*cp.m_lateralFrictionDir1.cross(cp.m_normalWorldOnB);
	
	cp.m_contactMotion1 = 1.f;
	//cp.m_contactCFM2 = 0.1;
	//cp.m_combinedFriction = 10;
	//cp.m_combinedRestitution = calculateCombinedRestitution(restitution0,restitution1);
	return true;
}