如何在Swift中给SKLabelNode加下划线？

let labelNode = SKLabelNode(text: "Hello World")

labelNode.fontName = "Helvetica"
labelNode.fontSize = 20
labelNode.fontColor = UIColor.white

let underlineNode = SKShapeNode(rectOf: CGSize(width: labelNode.frame.width, height: 1))
underlineNode.fillColor = UIColor.white
underlineNode.position = CGPoint(x: labelNode.position.x, y: labelNode.position.y - labelNode.frame.height/2)

labelNode.parent?.addChild(underlineNode)

import SpriteKit

class GameScene: SKScene {
    override func didMove(to view: SKView) {
        let labelNode = SKLabelNode(text: "Hello World")
        labelNode.fontName = "Helvetica"
        labelNode.fontSize = 20
        labelNode.fontColor = UIColor.white
        addChild(labelNode)
        
        let underlineNode = SKShapeNode(rectOf: CGSize(width: labelNode.frame.width, height: 1))
        underlineNode.fillColor = UIColor.white
        underlineNode.position = CGPoint(x: labelNode.position.x, y: labelNode.position.y - labelNode.frame.height/2)
        labelNode.parent?.addChild(underlineNode)
    }
}