ios - 将 CGGradient 转换为 CAGradientLayer

Question

我正在使用 PaintCode StyleKit 生成一堆渐变，但 PaintCode 将它们导出为CGGradient. 我想将这些渐变添加到layer. 是否可以将 a 转换CGGradient为 a CAGradientLayer？

Answer 1

不，CAGradientLayer 的意义在于你可以向它描述你想要的渐变，它会为你绘制渐变。你已经过了那一步；你已经描述了你想要的渐变（到 PaintCode而不是到 CAGradientLayer），因此你已经有了你想要的渐变。因此，你甚至想使用 CAGradientLayer 都是愚蠢的，因为如果你要这样做，你为什么首先使用 PaintCode？只需将 CGGradient 本身绘制到图像、视图甚至图层中。

Answer 2

您无法从 CGGradient 中获取颜色，但您可以使用相同的值来设置 CAGradientLayer 的colors和locations属性。也许它会帮助您修改生成的PCGradient类以将颜色和位置保留为可以传递给 CAGradientLayer 的 NSArray。

Answer 3

如果您有一个渐变库并且只是偶尔需要使用两种格式之一的渐变，这可能很重要。

是的，这是可能的，但需要一些数学才能从常规坐标系（x 值从 0 到宽度，y 值从 0 到高度）转换为 CAGradientLayer 使用的坐标系（x 值从 0 到 1和 y 值从 0 到 1)。而且它需要更多的数学运算（相当复杂）才能使斜率正确。

x 从 0 到 1 的距离取决于原始矩形的宽度。y 从 0 到 1 的距离将取决于原始矩形的高度。所以：

let convertedStartX = startX/Double(width)
let convertedStartY = startY/Double(height)
let convertedEndX = endX/Double(width)
let convertedEndY = endY/Double(height)

let intermediateStartPoint = CGPoint(x:convertedStartX,y:convertedStartY)
let intermediateEndPoint = CGPoint(x:convertedEndX,y:convertedEndY)

如果您的原始矩形是正方形，则此方法有效。否则，定义渐变角度的线的斜率将是错误的！要解决此问题，请参阅此处的出色答案：CAGradientLayer 对角渐变

如果您从那里选择实用程序，那么您可以如下设置最终转换的起点和终点，从上面已经调整的点值开始：

let fixedStartEnd:(CGPoint,CGPoint) = LinearGradientFixer.fixPoints(start: intermediateStartPoint, end: intermediateEndPoint, bounds: CGSize(width:width,height:height))

let myGradientLayer = CAGradientLayer()
myGradientLayer.startPoint = fixedStartEnd.0
myGradientLayer.endPoint = fixedStartEnd.1

这是一个完整结构的代码，您可以使用它来存储梯度数据并根据需要取回 CGGradients 或 CAGradientLayers：

import UIKit

struct UniversalGradient {

    //Doubles are more precise than CGFloats for the
    //calculations needed to convert start and end
    //to CAGradientLayers 1...0 format

    var startX: Double
    var startY: Double
    var endX: Double
    var endY: Double

    let options: CGGradientDrawingOptions = [.drawsBeforeStartLocation, .drawsAfterEndLocation]

    //for CAGradientLayer
    var colors: [UIColor]
    var locations: [Double]

    //computed conversions
    private var myCGColors: [CGColor] {
        return self.colors .map {color in color.cgColor}
    }

    private var myCGFloatLocations: [CGFloat] {
        return self.locations .map {location in CGFloat(location)}
    }

    //computed properties
    var gradient: CGGradient {
        return CGGradient(colorsSpace: nil, colors: myCGColors as CFArray, locations: myCGFloatLocations)!
    }

    var start: CGPoint {
        return CGPoint(x: startX,y: startY)
    }
    var end: CGPoint {
        return CGPoint(x: endX,y: endY)
    }

    //can't use computed property here
    //since we need details of the specific environment's bounds to be passed in
    //so this will be an instance function

    func gradientLayer(width: CGFloat, height: CGFloat) -> CAGradientLayer {

        //convert location x and y values from full coordinates to 0...1 for start and end
        //this works great for position, but it gets the slope incorrect if the view is not square

        //this is because the gradient is not drawn with the final scale
        //it is drawn while the view is square, and then it gets stretched, changing the angle
        //https://stackoverflow.com/questions/38821631/cagradientlayer-diagonal-gradient

        let convertedStartX = startX/Double(width)
        let convertedStartY = startY/Double(height)
        let convertedEndX = endX/Double(width)
        let convertedEndY = endY/Double(height)

        let intermediateStartPoint = CGPoint(x:convertedStartX,y:convertedStartY)
        let intermediateEndPoint = CGPoint(x:convertedEndX,y:convertedEndY)

        let fixedStartEnd:(CGPoint,CGPoint) = LinearGradientFixer.fixPoints(start: intermediateStartPoint, end: intermediateEndPoint, bounds: CGSize(width:width,height:height))

        let myGradientLayer = CAGradientLayer()
        myGradientLayer.startPoint = fixedStartEnd.0
        myGradientLayer.endPoint = fixedStartEnd.1

        myGradientLayer.locations = self.locations .map {location in NSNumber(value: location)}
        myGradientLayer.colors = self.colors .map {color in color.cgColor}

        return myGradientLayer
    }

}