对 CAShapeLayer 应用渐变

Question

有人有将渐变应用于 CAShapeLayer 的经验吗？ CAShapeLayer 是一个很棒的图层类，但它似乎只支持纯色填充，而我希望它有一个渐变填充（实际上是一个动画渐变）。

与 CAShapeLayer 相关的一切（阴影、形状、笔触颜色、可动画的形状路径）都很棒。

我尝试在 CAShapeLayer 中放置一个 CAGradientLayer，或者确实将 CAShapeLayer 设置为 GradientLayer 的蒙版并将两者都添加到容器层，但这些都没有正确的结果。

我应该继承 CAShapeLayer，还是有更好的方法？

谢谢。

Answer 1

非常感谢@Palimondo 的出色回答！

如果有人正在寻找此解决方案的 Swift 4 + 填充动画代码：

    let myView = UIView(frame: .init(x: 0, y: 0, width: 200, height: 150))
    view.addSubview(myView)
    myView.center = view.center

    // Start and finish point
    let startPoint = CGPoint(x: myView.bounds.minX, y: myView.bounds.midY)
    let finishPoint = CGPoint(x: myView.bounds.maxX, y: myView.bounds.midY)

    // Path
    let path = UIBezierPath()
    path.move(to: startPoint)
    path.addLine(to: finishPoint)

    // Gradient Mask
    let gradientMask = CAShapeLayer()
    let lineHeight = myView.frame.height
    gradientMask.fillColor = UIColor.clear.cgColor
    gradientMask.strokeColor = UIColor.black.cgColor
    gradientMask.lineWidth = lineHeight
    gradientMask.frame = myView.bounds
    gradientMask.path = path.cgPath

    // Gradient Layer
    let gradientLayer = CAGradientLayer()
    gradientLayer.startPoint = CGPoint(x: 0.0, y: 0.5)
    gradientLayer.endPoint = CGPoint(x: 1.0, y: 0.5)

    // make sure to use .cgColor
    gradientLayer.colors = [UIColor.red.cgColor, UIColor.green.cgColor]
    gradientLayer.frame = myView.bounds
    gradientLayer.mask = gradientMask

    myView.layer.addSublayer(gradientLayer)

    // Corner radius
    myView.layer.cornerRadius = 10
    myView.clipsToBounds = true

额外。如果您还需要“填充动画”，请添加以下行：

    // Filling animation
    let animation = CABasicAnimation(keyPath: "strokeEnd")
    animation.fromValue = 0
    animation.duration = 10
    gradientMask.add(animation, forKey: "LineAnimation")

Answer 2

这是一个很好的解决方案，但是如果您在 CAShapeLayer 上创建一个类别而您没有立即看到该视图，您可能会遇到意想不到的问题。

见Setting correct frame of a newly created CAShapeLayer

底线，获取路径的边界，然后使用路径边界设置渐变蒙版的框架，并根据需要进行平移。这里的好处是，通过使用路径的边界而不是任何其他框架，渐变将只适合路径边界（假设这是您想要的）。

// Category on CAShapeLayer

CGRect pathBounds = CGPathGetBoundingBox(self.path);

CAShapeLayer *gradientMask = [CAShapeLayer layer];
gradientMask.fillColor = [[UIColor blackColor] CGColor];
gradientMask.frame = CGRectMake(0, 0, pathBounds.size.width, pathBounds.size.height);
gradientMask.path = self.path;

CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.startPoint = CGPointMake(0.5,1.0);
gradientLayer.endPoint = CGPointMake(0.5,0.0);
gradientLayer.frame = CGRectMake(0, 0, pathBounds.size.width, pathBounds.size.height);

NSMutableArray *colors = [NSMutableArray array];
for (int i = 0; i < 10; i++) {
    [colors addObject:(id)[[UIColor colorWithHue:(0.1 * i) saturation:1 brightness:.8 alpha:1] CGColor]];
}
gradientLayer.colors = colors;

[gradientLayer setMask:gradientMask];
[self addSublayer:gradientLayer];

Answer 3

您可以使用形状的路径来创建一个遮罩层并将其应用到渐变层上，如下所示：

UIView *v = [[UIView alloc] initWithFrame:self.window.frame];

CAShapeLayer *gradientMask = [CAShapeLayer layer];   
gradientMask.fillColor = [[UIColor clearColor] CGColor];
gradientMask.strokeColor = [[UIColor blackColor] CGColor];
gradientMask.lineWidth = 4;
gradientMask.frame = CGRectMake(0, 0, v.bounds.size.width, v.bounds.size.height);

CGMutablePathRef t = CGPathCreateMutable();    
CGPathMoveToPoint(t, NULL, 0, 0);
CGPathAddLineToPoint(t, NULL, v.bounds.size.width, v.bounds.size.height);

gradientMask.path = t;


CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.startPoint = CGPointMake(0.5,1.0);
gradientLayer.endPoint = CGPointMake(0.5,0.0);
gradientLayer.frame = CGRectMake(0, 0, v.bounds.size.width, v.bounds.size.height);
NSMutableArray *colors = [NSMutableArray array];
for (int i = 0; i < 10; i++) {
    [colors addObject:(id)[[UIColor colorWithHue:(0.1 * i) saturation:1 brightness:.8 alpha:1] CGColor]];
}
gradientLayer.colors = colors;

[gradientLayer setMask:gradientMask];
[v.layer addSublayer:gradientLayer];

如果您还想使用阴影，则必须在渐变层下方放置一个“复制”形状层，循环使用相同的路径参考。