Fusion of actuators_control in vtol_att_control

Hello, I am studying how px4 converts actuators_control to pwm value recently. To vtol_att_control (eg tailsitter.cpp), there is both actuator_controls_0 and actuator_controls_1, I am confusing how these two are fused together and then send to mixer. Anyone know which code does this work? Any suggestions will be appreciate!

Nice weekend!