画直线瞄准

Question

If you played Angry Birds or any Pool game before you would be familiar with what I'm trying to do, basically what I want is:

1- Draw a line in touchesMoved so that the player can know in which direction he is aiming.

2- I want the line to reflect in the right direction when it hits other objects. So far I have this:

Update:

   var ref = CGPathCreateMutable()

        override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {

            for touch in touches {
                let location = touch.locationInNode(self)

                let path = CGPathCreateMutable()
                CGPathMoveToPoint(ref, nil, position.x - 100 , position.y - 100 )
                CGPathAddLineToPoint(ref, nil, -location.x, -location.y)

                line.removeFromParent()
                line.path = ref

                line.strokeColor = UIColor.redColor()
                line.lineWidth = 20
                line.antialiased = true
                line.fillColor = UIColor.blueColor()
                addChild(line)
            }
        }

I added the - before location so that the line gets drawn in front of the node ao it gives better aiming sense, but that leave me with 2 problems:

1- I want the line to have a limit in which it gets in front of the node, but at the same time, I want its end to be the current touch location. ( Basically, I want it to go through the node)

2- I still don't know how can I make it reflect to the right angle when it hit a wall or something so it gives an idea of the node would bounce off that wall.

Answer 1

SpriteKit isn't drawing API. In SpriteKit you basically add elements to the scene and animate the elements. What you need to do is to delete previous line (if any) then add a new line to the scene every frame. Here is the pseudo code to give you idea how to do it:

class ParentNode: SKNode {

   private var lines = [SKShapeNode]()

    /// Called before each frame is rendered
    override func update(currentTime: CFTimeInterval) {
      self.drawLine()
    }

    func drawLine() {
      let _ = self.lines.map { $0.removeFromParent() }
      self.lines.removeAll()

      if let path = self.createDrawingPath() {
         let lineNode = SKShapeNode()
         lineNode.path = path
         lineNode.strokeColor = UIColor.whiteColor()
         lineNode.lineWidth = 3.0

         self.addChild(lineNode)
         self.lines.append(lineNode)
      }
   }
}

In your case just do the similar thing, I've used update to delete/add new line, but I guess you can use touchesMoved(touches:withEvent) to do it.

Answer 2

An alternative to deleting and adding a line node every frame, make a SKShapeNode of 1 pixel by 1 pixel, then scale on the x axis the distance of the from pt to the to pt, then rotate it. Use let angle = arctan2(P2_y - P1_y , P2_x - P1_x) (I believe arctan2 handles division by 0 for you) to get the angle