如何在屏幕上的某个点与用户的手指位置之间建立一条线连接？

Question

I'm making a game, but haven't been able to figure this out yet.

So, there's a little zappy ball of electricity at the bottom of the screen, and I want to make it so that – when you touch the screen – it makes a line of electricity, and connects it between the zappy ball and your finger. When you move your finger, the line shrinks or enlarges to fit the distance between the two.

Think of it like those electricity balls in real life. You touch your finger to it, the electricity redirects to your finger. When you move your finger, the line of electricity move with it, so it can find the electricity in your finger and pair up with it.

Answer 1

You can use an SKShapeNode to draw a line between two points. Create an SKShapeNode in touchesBegan . You can then modify its path based on touch location in touchesMoved .

var currentLine : SKShapeNode!

override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
    let touch = touches.anyObject() as UITouch?
    if let pointOfTouch = touch?.locationInNode(self) {
        currentLine = SKShapeNode()
        let pathToDraw = CGPathCreateMutable();
        CGPathMoveToPoint(pathToDraw, nil, 100.0, 100.0); // Change to zap
        CGPathAddLineToPoint(pathToDraw, nil, pointOfTouch.x, pointOfTouch.y);
        currentLine.path = pathToDraw
        self.addChild(currentLine)
    }
}

override func touchesMoved(touches: NSSet, withEvent event: UIEvent) {

    let touch = touches.anyObject() as UITouch?
    if let pointOfTouch = touch?.locationInNode(self) {
        let pathToDraw = CGPathCreateMutable();
        CGPathMoveToPoint(pathToDraw, nil, 100.0, 100.0); // Change to zap
        CGPathAddLineToPoint(pathToDraw, nil, pointOfTouch.x, pointOfTouch.y);
        currentLine.path = pathToDraw
    }
}