向 CAGradientLayer 添加蒙版使 UIBezierPath 消失

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【中文标题】向 CAGradientLayer 添加蒙版使 UIBezierPath 消失【英文标题】:Adding a mask to CAGradientLayer makes UIBezierPath disappear 【发布时间】:2017-12-20 02:09:02 【问题描述】:

我想为带有渐变的视图添加内边框。以下代码有效并给了我这个结果

import UIKit

class InnerGradientBorderView: UIView 
    override init(frame: CGRect) 
        super.init(frame: frame)
        backgroundColor = UIColor.clear
    

    required init?(coder aDecoder: NSCoder) 
        super.init(coder: aDecoder)
        backgroundColor = UIColor.clear
    

    override func draw(_ rect: CGRect) 
        super.draw(rect)

        addGradientInnerBorder(width: 8, color: FlatWhite())
    

    func addGradientInnerBorder(width: CGFloat, color: UIColor) 

        // Setup
        let topLeftO = CGPoint(x: 0, y: 0)
        let topLeftI = CGPoint(x: width, y: width)

        let topRightO = CGPoint(x: frame.width, y: 0)
        let topRightI = CGPoint(x: frame.width - width, y: width)

        let bottomLeftO = CGPoint(x: 0, y: frame.height)
        let bottomLeftI = CGPoint(x: width, y: frame.height - width)

        let bottomRightO = CGPoint(x: frame.width, y: frame.height)
        let bottomRightI = CGPoint(x: frame.width - width, y: frame.height - width)

        // Top
        let topPoints = [topLeftO, topLeftI, topRightI, topRightO, topLeftO]
        let topGradientPoints = [CGPoint(x: 0, y: 0), CGPoint(x: 0, y: 1)]
        addGradientToBeizerPath(path: addClosedPathForPoints(points: topPoints), color: color, gradientPoints: topGradientPoints)

        // Left
        let leftPoints = [topLeftO, topLeftI, bottomLeftI, bottomLeftO, topLeftO]
        let leftGradientPoints = [CGPoint(x: 0, y: 0), CGPoint(x: 1, y: 0)]
        addGradientToBeizerPath(path: addClosedPathForPoints(points: leftPoints), color: color, gradientPoints: leftGradientPoints)

        // Right
        let rightPoints = [topRightO, topRightI, bottomRightI, bottomRightO, topRightO]
        let rightGradientPoints = [CGPoint(x: 1, y: 0), CGPoint(x: 0, y: 0)]
        addGradientToBeizerPath(path: addClosedPathForPoints(points: rightPoints), color: color, gradientPoints: rightGradientPoints)

        // Bottom
        let bottomPoints = [bottomLeftO, bottomLeftI, bottomRightI, bottomRightO, bottomLeftO]
        let bottomGradientPoints = [CGPoint(x: 0, y: 1), CGPoint(x: 0, y: 0)]
        addGradientToBeizerPath(path: addClosedPathForPoints(points: bottomPoints), color: color, gradientPoints: bottomGradientPoints)
    

    func addClosedPathForPoints(points: [CGPoint]) -> UIBezierPath? 
        guard points.count == 5 else  return nil 

        let path = UIBezierPath()
        path.move(to: points[0])
        path.addLine(to: points[1])
        path.addLine(to: points[2])
        path.addLine(to: points[3])
        path.addLine(to: points[4])

        path.close()

        return path
    

    func addGradientToBeizerPath(path: UIBezierPath?, color: UIColor, gradientPoints: [CGPoint]) 
        guard let path = path, gradientPoints.count == 2 else  return 

        let gradient = CAGradientLayer()
        gradient.frame = path.bounds
        gradient.colors = [color.cgColor, UIColor.clear.cgColor]
        gradient.startPoint = gradientPoints[0]
        gradient.endPoint = gradientPoints[1]

//        let shapeMask = CAShapeLayer()
//        shapeMask.path = path.cgPath
//        gradient.mask = shapeMask

        self.layer.insertSublayer(gradient, at: 0)
    

你会注意到边缘看起来不太好。为了解决这个问题,我给边缘一个角度。当我用这个角度对这个渐变应用蒙版时,右边和底部的路径会像这样消失:

我在这里所做的只是使用一些封闭的 bezierPaths 并对它们应用渐变。如果渐变有遮罩(注释代码未注释),则其中两条路径消失。我有一种不明白的感觉,所以希望这里有人能告诉我如何正确使用 CAShapeLayer。

【问题讨论】:

我不明白您为什么要从 draw 方法内部将 CAGradientLayer 添加到视图的 layer - 这对我来说感觉不对。你能解释一下你想要达到的目标吗? 我添加这个是可调整大小的。而且由于每当需要绘制或重绘视图时都会调用draw 方法,所以我想我会在那里完成工作。您有更好的实施方案吗? 是的,layoutSubviews 或其他地方。您应该只覆盖draw 来实际执行渲染,而不是更改层层次结构。由于您通过draw 调用插入图层,并且从不删除我可以看到的图层,因此您最终会得到数百个图层,不是吗?我实际上很难理解你想要实现的目标...... 我明白你的意思。不知道我在想什么。让我通过代码审查来解决这个问题,我将用更有意义的代码更新我的问题。感谢您的回复。 【参考方案1】:

This comment 到 CALayer mask property 完美解释:

遮罩层位于被遮罩层的坐标系中,就像它是子层一样。

在您的情况下,右侧和底部渐变层的原点不是 在封闭视图的(0, 0),但在(frame.width - width, 0)(frame.height - width, 0) 分别。 另一方面,点的坐标 oshapeMask.path 相对于封闭视图的(0, 0)

一个可能的简单解决方法是转换坐标系 形状图层,使其使用与点相同的坐标 给定路径的:

    let gradient = CAGradientLayer()
    gradient.frame = path.bounds
    gradient.bounds = path.bounds // <<--- ADDED HERE!
    gradient.colors = [color.cgColor, UIColor.clear.cgColor]
    gradient.startPoint = gradientPoints[0]
    gradient.endPoint = gradientPoints[1]

    let shapeMask = CAShapeLayer()
    shapeMask.path = path.cgPath
    gradient.mask = shapeMask

    self.layer.addSublayer(gradient)

【讨论】:

这解决了这个问题。谢谢!

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