Wheel around center point

wheel_center.swift

// This would be the public method callled to start a wheel
func wheelToAngle(angle:CGFloat) {
    self.wheelAngle = angle
    self.wheeling = true
}

// This would run each game loop to perform the wheel
func wheel() {

    // Hard code the speed of the turn. Each frame, move 0.003 radians until we reach target.
    let radian = self.formation!.heading - 0.003
    
    // If we have wheeled past our target angle, stop wheeling. Process is complete.
    if(radian <= self.wheelAngle) {
        radian = self.wheelAngle
        self.wheeling = false
    }
        
    // Only do math functions once
    let cosRadian = cos(radian)
    let sinRadian = sin(radian)

    // Loop over each unit, and caluclate the target coordinates given the 0.003 rotation.
    for (index, unit) in enumerate(self.units) {
        let vector = self.formation!.getVectorAtPosition(index)
        let newX  = vector.dx * cosRadian - vector.dy * sinRadian
        let newY = vector.dx * sinRadian + vector.dy * cosRadian
        unit.moveToPoint(CGPoint(x:newX, y:newY), {})
    }

    // Update formation to reflect our new heading
    self.formation!.heading = radian
}