Nice been looking for a diagram like that. From reading through the source the control algorithms are from this paper,
Mellinger, Daniel, and Vijay Kumar. "Minimum snap trajectory generation and control for quadrotors." Robotics and Automation (ICRA), 2011 IEEE International Conference on. IEEE, 2011.
Any idea how close those algorithms are implemented in PX4? I'd like to use that as a benchmark for our own development.