https://github.com/pgorzelany/ScratchCardView
這有一個實現(xiàn)刮獎效果的第三方,一個灰色遮罩,手指劃過會顯現(xiàn)圖片內(nèi)容.
如圖:

效果圖

看到效果第一時間,認為是在imageView 上方遮蓋一層灰色 View ,在手指劃過時,路徑變成透明,以達到效果.當然,現(xiàn)實中是這樣實現(xiàn)的沒錯.
但是,在運行 demo 時,看到層級結(jié)構(gòu)
當相關(guān)如下時:

效果

層級結(jié)構(gòu)

????

頂著崩壞的世界觀繼續(xù)看源碼
直到

        canvasMaskView.backgroundColor = UIColor.clear
        canvasMaskView.strokeColor = UIColor.orange
        canvasMaskView.lineWidht = scratchWidth
        contentViewContainer.mask = canvasMaskView

canvasMaskView 即 我寫了 Hi 的圖層

mask 是什么屬性? 點擊去還是系統(tǒng)的屬性?

于是去百了個度 看到文章
http://www.reibang.com/p/e4ac8266d9f0
恍然大悟! 我的世界觀得以修正,謝謝!

說:

UIView有一個maskView屬性（遮罩），這個屬性是通過改變alpha通道來改變透明度的荷并，可以理解為maskview將自己“投影”到view上，實現(xiàn)改變alpha一樣的效果。

1.設(shè)置了遮罩屬性后view只顯示和遮罩重疊的區(qū)域呜达。

2.通過改變遮罩的alpha和顏色實現(xiàn)透明颂郎、半透明的效果膘茎。

至于劃線部分.代碼非常簡單(以下為框架:ScratchCardView 中摘抄)

import UIKit

class CanvasView: UIView {
    
    // MARK: Properties
    
    @IBInspectable var lineWidht: CGFloat = 1
    @IBInspectable var strokeColor = UIColor.red
    
    fileprivate var paths: [CGMutablePath] = []
    fileprivate var currentPath: CGMutablePath?
    
    // MARK: Lifecycle
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        self.configureView()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        
        self.configureView()
    }
    
    init(strokePaths paths: [CGMutablePath]) {
        self.init()
        
        self.paths = paths
    }
    
    override func draw(_ rect: CGRect) {
        let context = UIGraphicsGetCurrentContext()
        for path in self.paths + [self.currentPath].flatMap({$0}) {
            context?.addPath(path)
            context?.setLineWidth(lineWidht)
            context?.strokePath()
        }
    }
    
    // MARK: Actions
    
    func panGestureRecognized(_ recognizer: UIPanGestureRecognizer) {
        let location = recognizer.location(in: self)
        
        switch recognizer.state {
        case .began:
            self.beginPath(at: location)
        case .changed:
            self.addLine(to: location)
        default:
            self.closePath()
        }
    }
    
    // MARK: Public methods
    
    func beginPath(at point: CGPoint) {
        self.currentPath = CGMutablePath()
        self.currentPath?.move(to: point)
    }
    
    func addLine(to point: CGPoint) {
        self.currentPath?.addLine(to: point)
        self.setNeedsDisplay()
    }
    
    func closePath() {
        if let currentPath = self.currentPath {
            self.paths.append(currentPath)
        }
        self.currentPath = nil
        self.setNeedsDisplay()
    }
    
    func clear() {
        self.paths = []
        self.setNeedsDisplay()
    }
    
    // MARK: Private Methods
    
    fileprivate func configureView() {
        self.addGestureRecognizers()
    }
    
    fileprivate func addGestureRecognizers() {
        let panRecognizer = UIPanGestureRecognizer(target: self, action: #selector(panGestureRecognized))
        self.addGestureRecognizer(panRecognizer)
    }
}