使用 Swift 3.0 实时画线 [英] Draw a line realtime with Swift 3.0

问题描述

我正在尝试在 UIImageView 上绘图.使用 Swift 1.2 我能够让它工作，但我不得不将它转换为 Swift 3.0 并且我无法让它工作.

I'am trying to draw on a UIImageView. With Swift 1.2 I was able to get it to work, but I had to convert it to swift 3.0 and I just can't get it to work.

它需要做的就是用手指准确地画出你在屏幕上画的东西.

What it needs to do is draw exactly what you draw on the screen with your finger.

代码没有给出任何错误，但只是不显示任何内容.

The codes gives no errors, but just does not display anything.

变量；

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

代码；

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)
    }

推荐答案

你必须开始图像上下文:

You have to begin the image context:

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

您还必须对路径进行描边:

You also have to stroke the path:

context?.strokePath()

您也没有绘制上一张图片:

You also are not drawing the previous image:

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

因此:

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()
}

这篇关于使用 Swift 3.0 实时画线的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！