Code:

static bool CustomMaterialCombinerCallback(btManifoldPoint& cp,const btCollisionObjectWrapper* colObj0Wrap,int partId0,int index0,const btCollisionObjectWrapper* colObj1Wrap,int partId1,int index1){btAdjustInternalEdgeContacts(cp,colObj1Wrap,colObj0Wrap, partId1,index1);//if (enable){//btAdjustInternalEdgeContacts(cp,colObj1,colObj0, partId1,index1, BT_TRIANGLE_CONVEX_BACKFACE_MODE);//btAdjustInternalEdgeContacts(cp,colObj1,colObj0, partId1,index1, BT_TRIANGLE_CONVEX_DOUBLE_SIDED+BT_TRIANGLE_CONCAVE_DOUBLE_SIDED);}float friction0 = colObj0Wrap->getCollisionObject()->getFriction();float friction1 = colObj1Wrap->getCollisionObject()->getFriction();float restitution0 = colObj0Wrap->getCollisionObject()->getRestitution();float restitution1 = colObj1Wrap->getCollisionObject()->getRestitution();if (colObj0Wrap->getCollisionObject()->getCollisionFlags() & btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK){friction0 = 1.0;//partId0,index0restitution0 = 0.f;}if (colObj1Wrap->getCollisionObject()->getCollisionFlags() & btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK){if (index1&1){friction1 = 1.0f;//partId1,index1} else{friction1 = 0.f;}restitution1 = 0.f;}cp.m_combinedFriction = calculateCombinedFriction(friction0,friction1);cp.m_combinedRestitution = calculateCombinedRestitution(restitution0,restitution1);//cp.m_combinedFriction = calculateCombinedFriction(0.0,0.0);//cp.m_combinedRestitution = calculateCombinedRestitution(0.0,0.0);//this return value is currently ignored, but to be on the safe side: return false if you don't calculate frictionreturn true;}