绘制完美的圆角线，Swift

Question

我正在开发一个绘图应用原型，我想要实现的是完美的圆角线。我已经通过曲线实现了绘图，但我的线条看起来还是有点像素化。

这是我的结果：

这就是我想要实现的目标：

    class ViewController: UIViewController {
        private var currentPoint: CGPoint?
        private var previousPoint1: CGPoint?
        private var previousPoint2: CGPoint?
        private var lineColor = UIColor.black
        private var lineWidth = CGFloat(10)
        private var lineAlpha = CGFloat(1)
        @IBOutlet private weak var imageView: UIImageView!
    
        override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
            guard let touch = touches.first else { return }
            
            previousPoint1 = touch.previousLocation(in: self.view)
            currentPoint = touch.location(in: self.view)
        }
    
        override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
            guard let touch = touches.first else { return }
            
            previousPoint2 = previousPoint1
            previousPoint1 = touch.previousLocation(in: self.view)
            currentPoint = touch.location(in: self.view)
            
            let mid1 = middlePoint(previousPoint1!, previousPoint2: previousPoint2!)
            let mid2 = middlePoint(currentPoint!, previousPoint2: previousPoint1!)
            
            draw(move: CGPoint(x: mid1.x, y: mid1.y), to: CGPoint(x: mid2.x, y: mid2.y), control: CGPoint(x: previousPoint1!.x, y: previousPoint1!.y))
        }
    
        public override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
            touchesMoved(touches, with: event)
        }
    
        private func middlePoint(_ previousPoint1: CGPoint, previousPoint2: CGPoint) -> CGPoint {
            return CGPoint(x: (previousPoint1.x + previousPoint2.x) * 0.5, y: (previousPoint1.y + previousPoint2.y) * 0.5)
        }
    
        func draw(move: CGPoint, to: CGPoint, control: CGPoint) {
            UIGraphicsBeginImageContext(view.frame.size)
            guard let ctx = UIGraphicsGetCurrentContext() else { return }
            imageView.image?.draw(in: view.bounds)
            ctx.move(to: move)
            ctx.addQuadCurve(to: to, control: control)
            ctx.setLineCap(.round)
            ctx.setLineJoin(.round)
            ctx.setLineWidth(lineWidth)
            ctx.setStrokeColor(lineColor.cgColor)
            ctx.setBlendMode(.normal)
            ctx.setAlpha(lineAlpha)
            ctx.strokePath()
            let finalImage = UIGraphicsGetImageFromCurrentImageContext()
            imageView.image = finalImage
            UIGraphicsEndImageContext()
        }
    }

附：我想通过上下文绘制，而不是使用drawRect

Answer 1

这里的问题是您创建的 imageContext 的比例不正确。与其使用 UIGraphicsBeginImageContext 创建上下文，不如尝试使用 UIGraphicsBeginImageContextWithOptions 创建它并将比例值设为 0。当您指定比例值为 0 时，比例因子设置为设备主屏幕的比例因子。更新后的代码 sn-p 如下所示。

func draw(move: CGPoint, to: CGPoint, control: CGPoint) {
        UIGraphicsBeginImageContextWithOptions(view.frame.size, false, 0)
        guard let ctx = UIGraphicsGetCurrentContext() else { return }
        imageView.image?.draw(in: view.bounds)
        ctx.move(to: move)
        ctx.addQuadCurve(to: to, control: control)
        ctx.setLineCap(.round)
        ctx.setLineJoin(.round)
        ctx.setLineWidth(lineWidth)
        ctx.setStrokeColor(lineColor.cgColor)
        ctx.setBlendMode(.normal)
        ctx.setAlpha(lineAlpha)
        ctx.strokePath()
        let finalImage = UIGraphicsGetImageFromCurrentImageContext()
        imageView.image = finalImage
        UIGraphicsEndImageContext()
    }