Swift Pong(No SpriteKit): How to calculate ball angles to move ball

Question

I'm trying to make the game Pong using Swift, but without using SpriteKit. So far, I have been able to successfully draw a rectangle on my view, and I am able to drag this around the screen. This is my current code:

import UIKit

class PongView: UIView {
    lazy var paddle: CGRect = {
        return CGRect(x: 200,
                             y: 200,
                             width: self.frame.width / 6,
                             height: self.frame.height / 60)
    }()
    var movePaddle = false

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        let gesture = UIPanGestureRecognizer(target: self, action: #selector(dragPaddle(recognizer:)))
        addGestureRecognizer(gesture)
    }

    override func draw(_ rect: CGRect) {
        drawPaddle(rect)
    }

    func drawPaddle(_ rect: CGRect) {
        let path = UIBezierPath(rect: paddle)
        UIColor.black.set()
        path.fill()
    }

    func paddleInBounds() -> Bool {
        //padding vars are calculated in another file
        return (paddle.minX >= frame.minX + leftPadding) &&
               (paddle.maxX <= frame.maxX - rightPadding) &&
               (paddle.minY >= frame.minY + topPadding) &&
               (paddle.maxY <= frame.maxY - bottomPadding)
    }

    func setPaddleInBounds() {
        if (paddle.minX < frame.minX + leftPadding) {
            paddle.origin.x = frame.minX + leftPadding
        }
        if (paddle.maxX > frame.maxX - rightPadding) {
            paddle.origin.x = frame.maxX - rightPadding - paddle.width
        }
        if (paddle.minY < frame.minY + topPadding) {
            paddle.origin.y = frame.minY + topPadding
        }
        if (paddle.maxY > frame.maxY - bottomPadding) {
            paddle.origin.y = frame.maxY - bottomPadding - paddle.height
        }
    }

    @objc func dragPaddle(recognizer: UIPanGestureRecognizer) {
        print(paddle.origin)
        print(paddle.minX)
        print(paddle.minY)
        if paddleInBounds() {
            let translation = recognizer.translation(in: self)
            paddle.origin = CGPoint(x: paddle.minX + translation.x, y: paddle.minY + translation.y)
            recognizer.setTranslation(CGPoint.zero, in: self)
            setNeedsDisplay()
        } else {
            setPaddleInBounds()
        }
    }
}

Now I would like to create the ball. I'm not sure how to begin, though. Collisions should be easy:

if (ball coordinates are within boundaries) || 
   (ball coordinates touch paddle coordinates) {
    //collision detected
}

But without SpriteKit, I'm not sure how to calculate ball bouncing angles and move the ball accordingly, which are the main parts of the game. Any suggestions?

Just so it's said, UIKit is not optimal for building a game. — swift-lynx, Jul 04 '19 at 09:24

score 5 · Accepted Answer · answered Jul 02 '19 at 06:56

Simply put, you need to reverse the ball velocity 'x' if reached x-boundary and 'y' if reached y-boundary.

Considering no friction or acceleration any and no other factors to effect the velocity. Lets say the ball is traveling 60 degrees towards bottom right and hits right boundary. It needs to travel below on same 'y' velocity while returning towards left with same 'x' velocity. And as it hits bottom boundary, it will still move towards left, while returning towards top with same 'y' velocity.

var posX = 0
var posY = 0
var velX = 5
var velY = 8

func moveBall(){
    posX += velX
    posY += velY
    if collideOnXBoundary {
        velX = -velX
    }
    if collideOnYBoundary {
        velY = -velY
    }
}

You can create a whole physics for ball using this velocity. Change its value to speed up, use friction to slow it down as it moves, use acceleration, torque etc to create different mechanisms.

Hey @Alok, thank you so much for your detailed answers! I and my team stuck on an issue for days ah :/ I posted an interesting question: https://stackoverflow.com/questions/63662318/arkit-apply-filter-cifilter-to-a-specific-part-vertex-of-an-arfaceanchor Would love your suggestions! — Roi Mulia, Aug 31 '20 at 07:36

Swift Pong(No SpriteKit): How to calculate ball angles to move ball

1 Answers1