// functions for calculating steering values.
@lazyglobal off.

function GetPitch {
  parameter v is SHIP:FACING:FOREVECTOR.
  return 90 - vectorangle(SHIP:UP:FOREVECTOR, v).
}

function GetAscentVector {
  parameter minPitch.
  // face prograde, but hold a solid eastern heading and don't
  // rotate the ship
  local newHeading is lookdirup(SHIP:SRFPROGRADE:FOREVECTOR,
    heading(90, 0, 270):TOPVECTOR).
  if GetPitch(newHeading:FOREVECTOR) < minPitch {
    set newHeading to heading(90, minPitch, 270).
  }
  return newHeading.
}

function AddCircularizationNode {
  parameter usePeriapsis is false.
  local target is SHIP:ORBIT:APOAPSIS.
  local t is TIME + SHIP:ORBIT:ETA:APOAPSIS.
  if usePeriapsis {
    set target to SHIP:ORBIT:PERIAPSIS.
    set t to SHIP:ORBIT:ETA:PERIAPSIS.
  }
  local n is Node(t, 0, 0, 0).
  add(n).
 
  local epsilon is 100.
  lock diff to n:ORBIT:APOAPSIS - n:ORBIT:PERIAPSIS.
  local pid is PIDLoop(0.05, 0.006, 0.006).
  set pid:EPSILON to epsilon.
  set pid:SETPOINT to n:ORBIT:APOAPSIS.
  
  until abs(diff) < epsilon {
    print diff.
    set n:PROGRADE to pid:Update(TIME:SECONDS, n:ORBIT:PERIAPSIS).
    wait 0.001.
  }
}