Route distance
Hello XBleed,
Also in a Boeing, it is like the previous poster states: distance from present position to active waypoint and then the route along the string of waypoints to destination.
Whether the FMC/FMGS just takes straight line distance from PPOS to active waypoint, or whether it makes an allowance for turn circle, I am not sure of.
When being vectored to final, the most convenient way to clean up the waypoints is to create an intercept leg to the glidepath intercept waypoint.(Airbus drivers, don't forget to disarm NAV). In that way, NAV or LNAV will be available for missed approach guidance.