void _UnlockProperty(GraphicEntityMutexFlag flag)
{
mutex ^= flag;
// if every other property is released, graphic entity
// can be deleted as well
if (mutex == GraphicEntityMutexFlag.Existence)
{
mutex = GraphicEntityMutexFlag.None;
}
}
void _LockProperty(GraphicEntityMutexFlag flag)
{
//
mutex |= flag | GraphicEntityMutexFlag.Existence;
}