使用Swift 3.0實時繪制一條線

Question

我試圖在UIImageView上繪圖。 使用Swift 1.2我能夠讓它工作，但我不得不將它轉換為swift 3.0而我無法讓它工作。

它需要做的是用手指准確地繪制你在屏幕上繪制的內容。

代碼沒有錯誤，但只是沒有顯示任何內容。

變量;

var lastPoint = CGPoint.zero
var red: CGFloat = 0.0
var green: CGFloat = 0.0
var blue: CGFloat = 0.0
var brushWidth: CGFloat = 10.0
var opacity: CGFloat = 1.0
var swiped = false

編碼;

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = false
    if let touch = touches.first {
        lastPoint = touch.location(in: self.view)
    }
}

func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint) {


    imageView.image?.draw(in: CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height))
    UIGraphicsBeginImageContext(self.imageView.bounds.size);
    let context = UIGraphicsGetCurrentContext()

        context?.move(to: fromPoint)
        context?.addLine(to: toPoint)

        context?.setLineCap(CGLineCap.round)
        context?.setLineWidth(brushWidth)
        context?.setStrokeColor(red: red, green: green, blue: blue, alpha: 1.0)
        context?.setBlendMode(CGBlendMode.normal)

        imageView.image = UIGraphicsGetImageFromCurrentImageContext()
        imageView.alpha = opacity
        UIGraphicsEndImageContext()

}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = true
    if let touch = touches.first {
        let currentPoint = touch.location(in: view)
        drawLineFrom(fromPoint: lastPoint, toPoint: currentPoint)

        lastPoint = currentPoint
    }
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    if !swiped {
                    // draw a single point
        self.drawLineFrom(fromPoint: lastPoint, toPoint: lastPoint)
    }

Answer 1

你必須開始圖像上下文：

UIGraphicsBeginImageContextWithOptions(view.bounds.size, false, 0)

你還必須克服這條道路：

context?.strokePath()

您也沒有繪制上一張圖片：

imageView.image?.draw(in: view.bounds)

從而：

func drawLine(from fromPoint: CGPoint, to toPoint: CGPoint) {
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, false, 0)

    imageView.image?.draw(in: view.bounds)

    let context = UIGraphicsGetCurrentContext()

    context?.move(to: fromPoint)
    context?.addLine(to: toPoint)

    context?.setLineCap(CGLineCap.round)
    context?.setLineWidth(brushWidth)
    context?.setStrokeColor(red: red, green: green, blue: blue, alpha: 1.0)
    context?.setBlendMode(CGBlendMode.normal)
    context?.strokePath()

    imageView.image = UIGraphicsGetImageFromCurrentImageContext()
    imageView.alpha = opacity
    UIGraphicsEndImageContext()
}