randomgamescene.swift

    class GameScene: SKScene {
      
      let ball  = SKSpriteNode(color: .blue,  size: CGSize(width:  50, height:  50))
      let table = SKSpriteNode(color: .green, size: CGSize(width: 500, height: 500))

      func balled() {
        ball.position.y += 100
        
        let pb = SKPhysicsBody(rectangleOf: ball.size)
         pb.usesPreciseCollisionDetection = true
        ball.physicsBody = pb
        addChild(ball)
      }
      
      func tabled() {
        let pb = SKPhysicsBody(rectangleOf: table.size)
         pb.affectedByGravity = false
         pb.allowsRotation = false
         pb.isDynamic = false
         pb.usesPreciseCollisionDetection = true
        table.physicsBody = pb
        addChild(table)
      }
      
        func keepBallOnTable() {
          if ball.frame.minY < table.frame.maxY {
            ball.position.y = table.frame.maxY + ball.size.height / 2 + 1
          }
        }

      override func didMove(to view: SKView) {
        balled()
        tabled()
      }
      
      override func mouseDown(with event: NSEvent) {
        keepBallOnTable()
      }
      
      override func mouseDragged(with event: NSEvent) {
        table.position.y = event.location(in: self).y
      }

      override func didFinishUpdate() {
        keepBallOnTable()
      }
    }