如何使用颜色渐变笔划绘制圆形路径

Question

我想在iOS和macOS上绘制一个带有颜色渐变笔画的圆圈，如下图所示：

有可能用CAShapeLayer或NSBezierPath / CGPath实现吗？还是其他任何方式？

Answer 1

在macOS 10.14及更高版本（以及iOS 12及更高版本）中，您可以使用CAGradientLayer创建type，然后用圆弧屏蔽它。例如，对于macOS：

.conic

或者，在iOS中：

class GradientArcView: NSView {
    var startColor: NSColor = .white { didSet { setNeedsDisplay(bounds) } }
    var endColor:   NSColor = .blue  { didSet { setNeedsDisplay(bounds) } }
    var lineWidth:  CGFloat = 3      { didSet { setNeedsDisplay(bounds) } }

    private let gradientLayer: CAGradientLayer = {
        let gradientLayer = CAGradientLayer()
        gradientLayer.type = .conic
        gradientLayer.startPoint = CGPoint(x: 0.5, y: 0.5)
        gradientLayer.endPoint = CGPoint(x: 1, y: 0.5)
        return gradientLayer
    }()

    override init(frame: CGRect = .zero) {
        super.init(frame: frame)

        configure()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        configure()
    }

    override func layout() {
        super.layout()

        updateGradient()
    }
}

private extension GradientArcView {
    func configure() {
        wantsLayer = true
        layer?.addSublayer(gradientLayer)
    }

    func updateGradient() {
        gradientLayer.frame = bounds
        gradientLayer.colors = [startColor, endColor].map { $0.cgColor }

        let radius = (min(bounds.width, bounds.height) - lineWidth) / 2
        let path = CGPath(ellipseIn: bounds.insetBy(dx: bounds.width / 2 - radius, dy: bounds.height / 2 - radius), transform: nil)
        let mask = CAShapeLayer()
        mask.fillColor = NSColor.clear.cgColor
        mask.strokeColor = NSColor.white.cgColor
        mask.lineWidth = lineWidth
        mask.path = path
        gradientLayer.mask = mask
    }
}

在早期的OS版本中，您必须手动执行某些操作，例如以不同颜色触摸一系列弧。例如，在macOS中：

@IBDesignable
class GradientArcView: UIView {
    @IBInspectable var startColor: UIColor = .white { didSet { setNeedsLayout() } }
    @IBInspectable var endColor:   UIColor = .blue  { didSet { setNeedsLayout() } }
    @IBInspectable var lineWidth:  CGFloat = 3      { didSet { setNeedsLayout() } }

    private let gradientLayer: CAGradientLayer = {
        let gradientLayer = CAGradientLayer()
        gradientLayer.type = .conic
        gradientLayer.startPoint = CGPoint(x: 0.5, y: 0.5)
        gradientLayer.endPoint = CGPoint(x: 1, y: 0.5)
        return gradientLayer
    }()

    override init(frame: CGRect = .zero) {
        super.init(frame: frame)

        configure()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        configure()
    }

    override func layoutSubviews() {
        super.layoutSubviews()

        updateGradient()
    }
}

private extension GradientArcView {
    func configure() {
        layer.addSublayer(gradientLayer)
    }

    func updateGradient() {
        gradientLayer.frame = bounds
        gradientLayer.colors = [startColor, endColor].map { $0.cgColor }

        let center = CGPoint(x: bounds.midX, y: bounds.midY)
        let radius = (min(bounds.width, bounds.height) - lineWidth) / 2
        let path = UIBezierPath(arcCenter: center, radius: radius, startAngle: 0, endAngle: 2 * .pi, clockwise: true)
        let mask = CAShapeLayer()
        mask.fillColor = UIColor.clear.cgColor
        mask.strokeColor = UIColor.white.cgColor
        mask.lineWidth = lineWidth
        mask.path = path.cgPath
        gradientLayer.mask = mask
    }
}

import Cocoa /// This draws an arc, of length `maxAngle`, ending at `endAngle. This is `@IBDesignable`, so if you /// put this in a separate framework target, you can use this class in Interface Builder. The only /// property that is not `@IBInspectable` is the `lineCapStyle` (as IB doesn't know how to show that). /// /// If you want to make this animated, just use a `CADisplayLink` update the `endAngle` property (and /// this will automatically re-render itself whenever you change that property). @IBDesignable class GradientArcView: NSView { /// Width of the stroke. @IBInspectable var lineWidth: CGFloat = 3 { didSet { setNeedsDisplay(bounds) } } /// Color of the stroke (at full alpha, at the end). @IBInspectable var strokeColor: NSColor = .blue { didSet { setNeedsDisplay(bounds) } } /// Where the arc should end, measured in degrees, where 0 = "3 o'clock". @IBInspectable var endAngle: CGFloat = 0 { didSet { setNeedsDisplay(bounds) } } /// What is the full angle of the arc, measured in degrees, e.g. 180 = half way around, 360 = all the way around, etc. @IBInspectable var maxAngle: CGFloat = 360 { didSet { setNeedsDisplay(bounds) } } /// What is the shape at the end of the arc. var lineCapStyle: NSBezierPath.LineCapStyle = .square { didSet { setNeedsDisplay(bounds) } } override func draw(_ dirtyRect: NSRect) { super.draw(dirtyRect) let gradations = 255 let startAngle = -endAngle + maxAngle let center = NSPoint(x: bounds.midX, y: bounds.midY) let radius = (min(bounds.width, bounds.height) - lineWidth) / 2 var angle = startAngle for i in 1 ... gradations { let percent = CGFloat(i) / CGFloat(gradations) let endAngle = startAngle - percent * maxAngle let path = NSBezierPath() path.lineWidth = lineWidth path.lineCapStyle = lineCapStyle path.appendArc(withCenter: center, radius: radius, startAngle: angle, endAngle: endAngle, clockwise: true) strokeColor.withAlphaComponent(percent).setStroke() path.stroke() angle = endAngle } } }

Answer 2

这是一些适合我的代码。其中有动画，但您可以使用相同的原理来制作带渐变的strokeEnd。

A.创建自定义视图'Donut'并将其放在标题中：

B.然后做了基本视图设置并编写了这两个方法：

@interface Donut : UIView
@property UIColor * fromColour;
@property UIColor * toColour;
@property UIColor * baseColour;
@property float lineWidth;
@property float duration;
-(void)layout;
-(void)animateTo:(float)percentage;

C.创建视图：

-(void)layout{

    //vars
    float dimension = self.frame.size.width;

    //1. layout views

    //1.1 layout base track
    UIBezierPath * donut = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(lineWidth/2, lineWidth/2, dimension-lineWidth, dimension-lineWidth)];
    CAShapeLayer * baseTrack = [CAShapeLayer layer];
    baseTrack.path = donut.CGPath;
    baseTrack.lineWidth = lineWidth;
    baseTrack.fillColor = [UIColor clearColor].CGColor;
    baseTrack.strokeStart = 0.0f;
    baseTrack.strokeEnd = 1.0f;
    baseTrack.strokeColor = baseColour.CGColor;
    baseTrack.lineCap = kCALineCapButt;
    [self.layer addSublayer:baseTrack];

    //1.2 clipView has mask applied to it
    UIView * clipView = [UIView new];
    clipView.frame =  self.bounds;
    [self addSubview:clipView];

    //1.3 rotateView transforms with strokeEnd
    rotateView = [UIView new];
    rotateView.frame = self.bounds;
    [clipView addSubview:rotateView];

    //1.4 radialGradient holds an image of the colours
    UIImageView * radialGradient = [UIImageView new];
    radialGradient.frame = self.bounds;
    [rotateView addSubview:radialGradient];



    //2. create colours fromColour --> toColour and add to an array

    //2.1 holds all colours between fromColour and toColour
    NSMutableArray * spectrumColours = [NSMutableArray new];

    //2.2 get RGB values for both colours
    double fR, fG, fB; //fromRed, fromGreen etc
    double tR, tG, tB; //toRed, toGreen etc
    [fromColour getRed:&fR green:&fG blue:&fB alpha:nil];
    [toColour getRed:&tR green:&tG blue:&tB alpha:nil];

    //2.3 determine increment between fromRed and toRed etc.
    int numberOfColours = 360;
    double dR = (tR-fR)/(numberOfColours-1);
    double dG = (tG-fG)/(numberOfColours-1);
    double dB = (tB-fB)/(numberOfColours-1);

    //2.4 loop through adding incrementally different colours
    //this is a gradient fromColour --> toColour
    for (int n = 0; n < numberOfColours; n++){
        [spectrumColours addObject:[UIColor colorWithRed:(fR+n*dR) green:(fG+n*dG) blue:(fB+n*dB) alpha:1.0f]];
    }


    //3. create a radial image using the spectrum colours
    //go through adding the next colour at an increasing angle

    //3.1 setup
    float radius = MIN(dimension, dimension)/2;
    float angle = 2 * M_PI/numberOfColours;
    UIBezierPath * bezierPath;
    CGPoint center = CGPointMake(dimension/2, dimension/2);

    UIGraphicsBeginImageContextWithOptions(CGSizeMake(dimension, dimension), true, 0.0);
    UIRectFill(CGRectMake(0, 0, dimension, dimension));

    //3.2 loop through pulling the colour and adding
    for (int n = 0; n<numberOfColours; n++){

        UIColor * colour = spectrumColours[n]; //colour for increment

        bezierPath = [UIBezierPath bezierPathWithArcCenter:center radius:radius startAngle:n * angle endAngle:(n + 1) * angle clockwise:YES];
        [bezierPath addLineToPoint:center];
        [bezierPath closePath];

        [colour setFill];
        [colour setStroke];
        [bezierPath fill];
        [bezierPath stroke];
    }

    //3.3 create image, add to the radialGradient and end
    [radialGradient setImage:UIGraphicsGetImageFromCurrentImageContext()];
    UIGraphicsEndImageContext();



    //4. create a dot to add to the rotating view
    //this covers the connecting line between the two colours

    //4.1 set up vars
    float containsDots = (M_PI * dimension) /*circumference*/ / lineWidth; //number of dots in circumference
    float colourIndex = roundf((numberOfColours / containsDots) * (containsDots-0.5f)); //the nearest colour for the dot
    UIColor * closestColour = spectrumColours[(int)colourIndex]; //the closest colour

    //4.2 create dot
    UIImageView * dot = [UIImageView new];
    dot.frame = CGRectMake(dimension-lineWidth, (dimension-lineWidth)/2, lineWidth, lineWidth);
    dot.layer.cornerRadius = lineWidth/2;
    dot.backgroundColor = closestColour;
    [rotateView addSubview:dot];


    //5. create the mask
    mask = [CAShapeLayer layer];
    mask.path = donut.CGPath;
    mask.lineWidth = lineWidth;
    mask.fillColor = [UIColor clearColor].CGColor;
    mask.strokeStart = 0.0f;
    mask.strokeEnd = 0.0f;
    mask.strokeColor = [UIColor blackColor].CGColor;
    mask.lineCap = kCALineCapRound;

    //5.1 apply the mask and rotate all by -90 (to move to the 12 position)
    clipView.layer.mask = mask;
    clipView.transform = CGAffineTransformMakeRotation(DEGREES_TO_RADIANS(-90.0f));

}

-(void)animateTo:(float)percentage {

    float difference = fabsf(fromPercentage - percentage);
    float fixedDuration = difference * duration;

    //1. animate stroke End
    CABasicAnimation * strokeEndAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
    strokeEndAnimation.duration = fixedDuration;
    strokeEndAnimation.fromValue = @(fromPercentage);
    strokeEndAnimation.toValue = @(percentage);
    strokeEndAnimation.fillMode = kCAFillModeForwards;
    strokeEndAnimation.removedOnCompletion = false;
    strokeEndAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    [mask addAnimation:strokeEndAnimation forKey:@"strokeEndAnimation"];

    //2. animate rotation of rotateView
    CABasicAnimation * viewRotationAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
    viewRotationAnimation.duration = fixedDuration;
    viewRotationAnimation.fromValue = @(DEGREES_TO_RADIANS(360 * fromPercentage));
    viewRotationAnimation.toValue = @(DEGREES_TO_RADIANS(360 * percentage));
    viewRotationAnimation.fillMode = kCAFillModeForwards;
    viewRotationAnimation.removedOnCompletion = false;
    viewRotationAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    [rotateView.layer addAnimation:viewRotationAnimation forKey:@"viewRotationAnimation"];

    //3. update from percentage
    fromPercentage = percentage;

}

D.动画视图：

Donut * donut = [Donut new];
donut.frame = CGRectMake(20, 100, 140, 140);
donut.baseColour = [[UIColor blackColor] colorWithAlphaComponent:0.2f];
donut.fromColour = [UIColor redColor];
donut.toColour = [UIColor blueColor];
donut.lineWidth = 20.0f;
donut.duration = 2.0f;
[donut layout];
[tasteView addSubview:donut];

E.说明：

甜甜圈视图从创建基本轨道，clipView，rotateView和radialGradient imageView开始。然后，它会计算您要在甜甜圈中使用的两种颜色之间的360种颜色。它通过增加颜色之间的rgb值来实现。然后使用这些颜色创建径向渐变图像并将其添加到imageView。因为我想使用kCALineCapRound，我添加了一个点来掩盖两种颜色相遇的地方。整个事情需要旋转-90度才能使其处于12点钟位置。然后将遮罩应用于视图，使其具有圆环形状。

随着蒙版的strokeEnd改变，它下面的视图'rotateView'也会旋转。这给人的印象是，只要它们处于同步状态，线就会增长/缩小。

您可能还需要这个：

[donut animateTo:0.5f];

Answer 3

由于你的路径是一个圆形，你所要求的数量相当于一个角度渐变，也就是说，当我们扫过一个圆形的圆形时，会改变颜色的一种馅饼。没有内置的方法可以做到这一点，但是有一个很棒的库可以帮到你：

#define DEGREES_TO_RADIANS(x) (M_PI * (x) / 180.0)

诀窍在于您绘制角度渐变，其中心位于圆的中心，然后在其上面放置一个遮罩，使其仅出现在您的圆形笔划的位置。

Answer 4

使用以下代码。经过测试，适用于iOS10 +

https://github.com/paiv/AngleGradientLayer

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