Moving SKSpriteNode to location of the touch

Question

Above is an image of my game. A top-down game. Wherever on the screen the player touches, I want the bullets to go to that location with a duration. I also want the

Answer 1

Here you go - a simple app with a ship you can drag around the screen and missiles that shoot towards the location of a touch.

If you touch the ship you can drag it around; touch outside the ship and a missile will shoot from the ship to the touch location.

import SpriteKit

class GameScene: SKScene {

var ship = SKSpriteNode()
var shipIsTouched = false
var missileDestination = CGPoint()
let missileSpeed: CGFloat = 800 // Points per second)
let missileFireRate : TimeInterval = 0.2 // Seconds between each missile

override func didMove(to view: SKView) {
    missileDestination = CGPoint(x: 0, y: (self.size.height / 2))
    createPlayerShip()
    let fire = SKAction.sequence([SKAction.run(fireMissile), SKAction.wait(forDuration: missileFireRate)])
    run(SKAction.repeatForever(fire))
}

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    if let touch = touches.first {
        if ship.contains(touch.location(in: self)) {
            shipIsTouched = true
        } else {
            missileDestination = touch.location(in: self)
            ship.zRotation = direction(to: missileDestination, from: ship.position) - CGFloat(Double.pi/2)
        }
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    if (shipIsTouched == true) {
        ship.position = (touches.first?.location(in: self))!
        ship.zRotation = direction(to: missileDestination, from: ship.position) - CGFloat(Double.pi/2)
    }
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    if shipIsTouched {
        shipIsTouched = false
    }
}

override func update(_ currentTime: TimeInterval) {
    // Called before each frame is rendered
}

func createPlayerShip() {
    ship = SKSpriteNode(imageNamed: "Spaceship")
    ship.zRotation = CGFloat(-Double.pi/2.0)
    ship.scale(to: CGSize(width: 150, height: 150))
    ship.position = CGPoint(x: -size.width/2 + 200, y: 0)

    addChild(ship)
}


func fireMissile() {
    let missile = SKSpriteNode(color: .white, size: CGSize(width: 50, height: 10))
    missile.position = ship.position

    let missileFlightTime = travelTime(to: missileDestination, from: ship.position, atSpeed: missileSpeed)
    missile.zRotation = direction(to: missileDestination, from: missile.position)

    addChild(missile)

    let missileMove = SKAction.move(to: missileDestination,
                                    duration: TimeInterval(missileFlightTime))
    let missileRemove = SKAction.removeFromParent()
    missile.run(SKAction.sequence([missileMove, missileRemove]))
}

func travelTime(to target : CGPoint, from : CGPoint, atSpeed speed : CGFloat) -> TimeInterval {
    let distance = sqrt(pow(abs(target.x - from.x),2) +
        pow(abs(target.y - from.y),2))
    return TimeInterval(distance/speed)
}


func direction(to target : CGPoint, from: CGPoint) -> CGFloat {
    let x = target.x - from.x
    let y = target.y - from.y
    var angle = atan(y / x)
    if x < 0 {
        angle = angle + CGFloat.pi
    }
    return angle
}
}

There's a bit of extra trickery to make the missiles speed consistent (since moveTo takes a time, not a speed, so if the destination was close the missiles would move slowly, and if further away they'd move faster) and to make the missiles rotate to face the destination.

You could create a curved path for the missiles to follow to the destination, which would look cool but may not be appropriate for your app.

EDIT:

If you want the ship stationary, and the missiles to follow your finger, replace all the code down to createPlayerShip with this (yes, we've lost touchesEnded() and update():

import SpriteKit

class GameScene: SKScene {

var ship = SKSpriteNode()
var missileDestination = CGPoint()
let missileSpeed: CGFloat = 800 // Points per second)
let missileFireRate : TimeInterval = 0.2 // Seconds between each missile

override func didMove(to view: SKView) {
    missileDestination = CGPoint(x: size.height/2, y: 0)
    createPlayerShip()
    let fire = SKAction.sequence([SKAction.run(fireMissile), SKAction.wait(forDuration: missileFireRate)])
    run(SKAction.repeatForever(fire))
}

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    if let touch = touches.first {
            missileDestination = touch.location(in: self)
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        missileDestination = (touches.first?.location(in: self))!
}