如何用有角度的渐变填充 CAShapeLayer

Question

如何用渐变和 45 度角填充 CAShapeLayer()？

例如，在图 1 中，以下代码绘制了一个正方形并将图层填充为蓝色 (UIColor.blueColor().CGColor)。

但是，如何使用 Image 2 中从蓝色到红色的 45 度角的渐变填充它（即 UIColor.blueColor().CGColor 到 UIColor.redColor().CGColor）？

代码：

let path = UIBezierPath()
path.moveToPoint(CGPoint(x: 0, y: 0))
path.addLineToPoint(CGPoint(x: 0, y: 100))
path.addLineToPoint(CGPoint(x: 100, y: 100))
path.addLineToPoint(CGPoint(x: 100, y: 0))
path.closePath()

let shape = CAShapeLayer()
shape.path = path.CGPath
shape.fillColor = UIColor.blueColor().CGColor

Answer 1

为什么不使用具有startPoint 和endPoint 属性的CAGradientLayer。

你可以这样做：

import UIKit
import PlaygroundSupport

let frame = CGRect(x: 0, y: 0, width: 100, height: 100)
let view = UIView(frame: frame)

PlaygroundPage.current.liveView = view

let path = UIBezierPath(ovalIn: frame)

let shape = CAShapeLayer()
shape.frame = frame
shape.path = path.cgPath
shape.fillColor = UIColor.blue.cgColor

let gradient = CAGradientLayer()
gradient.frame = frame
gradient.colors = [UIColor.blue.cgColor,
                   UIColor.red.cgColor]
gradient.startPoint = CGPoint(x: 0, y: 1)
gradient.endPoint = CGPoint(x: 1, y: 0)
gradient.mask = shape

view.layer.addSublayer(gradient)

注意：为圆形添加了贝塞尔路径，因为它可以在没有正方形遮罩的情况下工作。

Answer 2

轻松将渐变应用到 CALayer

Swift 4.2，Xcode 10.0

虽然上述解决方案仅适用于 45° 等微不足道的角度，但我的代码能够将渐变设置为任何给定角度。

public extension CALayer {

    public func applyGradient(of colors: UIColor..., atAngle angle: CGFloat) -> CAGradientLayer {
        let gradient = CAGradientLayer()
        gradient.frame = frame
        gradient.colors = colors
        gradient.calculatePoints(for: angle)
        gradient.mask = self
        return gradient
    }

}


public extension CAGradientLayer {

    /// Sets the start and end points on a gradient layer for a given angle.
    ///
    /// - Important:
    /// *0°* is a horizontal gradient from left to right.
    ///
    /// With a positive input, the rotational direction is clockwise.
    ///
    ///    * An input of *400°* will have the same output as an input of *40°*
    ///
    /// With a negative input, the rotational direction is clockwise.
    ///
    ///    * An input of *-15°* will have the same output as *345°*
    ///
    /// - Parameters:
    ///     - angle: The angle of the gradient.
    ///
    public func calculatePoints(for angle: CGFloat) {


        var ang = (-angle).truncatingRemainder(dividingBy: 360)

        if ang < 0 { ang = 360 + ang }

        let n: CGFloat = 0.5

        let tanx: (CGFloat) -> CGFloat = { tan($0 * CGFloat.pi / 180) }

        switch ang {

        case 0...45, 315...360:
            let a = CGPoint(x: 0, y: n * tanx(ang) + n)
            let b = CGPoint(x: 1, y: n * tanx(-ang) + n)
            startPoint = a
            endPoint = b

        case 45...135:
            let a = CGPoint(x: n * tanx(ang - 90) + n, y: 1)
            let b = CGPoint(x: n * tanx(-ang - 90) + n, y: 0)
            startPoint = a
            endPoint = b

        case 135...225:
            let a = CGPoint(x: 1, y: n * tanx(-ang) + n)
            let b = CGPoint(x: 0, y: n * tanx(ang) + n)
            startPoint = a
            endPoint = b

        case 225...315:
            let a = CGPoint(x: n * tanx(-ang - 90) + n, y: 0)
            let b = CGPoint(x: n * tanx(ang - 90) + n, y: 1)
            startPoint = a
            endPoint = b

        default:
            let a = CGPoint(x: 0, y: n)
            let b = CGPoint(x: 1, y: n)
            startPoint = a
            endPoint = b

        }
    }

}

---

用法：

let layer = CAShapeLayer()

// Setup layer...

// Gradient Direction: →
let gradientLayer1 = layer.applyGradient(of: UIColor.yellow, UIColor.red, at: 0)

// Gradient Direction: ↗︎
let gradientLayer2 = layer.applyGradient(of: UIColor.purple, UIColor.yellow, UIColor.green, at: -45)

// Gradient Direction: ←
let gradientLayer3 = layer.applyGradient(of: UIColor.yellow, UIColor.blue, UIColor.green, at: 180)

// Gradient Direction: ↓
let gradientLayer4 = layer.applyGradient(of: UIColor.red, UIColor.blue, at: 450)

---

数学解释

所以实际上我最近花了很多时间试图自己回答这个问题。下面是一些示例角度，只是为了帮助理解和可视化顺时针旋转方向。

如果您对我的计算方式感兴趣，我制作了一张表格，从 0° 到 360° 基本上可视化我在做什么。

Answer 3

我觉得是

shape.startPoint = CGPoint(x: 1.0, y: 0.0)
shape.endPoint = CGPoint(x: 0.0, y: 1.0)

，它是右下角的第一种颜色到左上角的第二种颜色。如果你想要右上角的第一种颜色和左下角的第二种颜色，那么你应该有

shape.startPoint = CGPoint(x: 1.0, y: 1.0)
shape.endPoint = CGPoint(x: 0.0, y: 0.0)

左上角第一种颜色，右下角第二种颜色

shape.startPoint = NSMakePoint(x: 0.0, y: 1.0)
shape.endPoint = NSMakePoint(x: 1.0, y: 0.0)

第一种颜色在左下角，第二种颜色在右上角

shape.startPoint = CGPoint(x: 0.0, y: 0.0)
shape.endPoint = CGPoint(x: 1.0, y: 1.0)

Answer 4

如果您的形状位于屏幕的左上角，@Alistra 答案有效。如果您尝试移动形状的位置，您会注意到形状被截断（如果它甚至显示出来，取决于您的 x 和 y 值）

要解决此问题，请为渐变层和形状层使用两个不同的框架。将形状图层的x,y 坐标设置为0,0。然后将渐变层的x,y 坐标设置为您希望它在屏幕上的位置。

    let gradientFrame = CGRect(x: 100,
                               y: 150,
                               width: 150,
                               height: 150)
    let circleFrame = CGRect(x: 0,
                             y: 0,
                             width: 150,
                             height: 150)
    let circle = CAShapeLayer()
    circle.frame = circleFrame
    circle.path = UIBezierPath(ovalIn: circleFrame).cgPath

    let gradient = CAGradientLayer()
    gradient.frame = gradientFrame
    gradient.startPoint = CGPoint(x: 0, y: 0)
    gradient.endPoint = CGPoint(x: 1, y: 1)
    gradient.colors = [UIColor.blue.cgColor,
                       UIColor.red.cgColor]
    gradient.mask = circle
    view.layer.addSublayer(gradient)

Answer 5

如果您不想使用 CAGradientLayer，根据 Noah Wilder 的回答，对于 Objective-C：

-(void)drawRect:(CGRect)rect {

//create theoretical circle
float w = self.frame.size.width;
float h = self.frame.size.height;

NSDictionary * points = [self pointsForAngle:angle width:w height:h];
CGPoint start = [points[@"start"] CGPointValue];
CGPoint end = [points[@"end"] CGPointValue];

//1. create vars
float increment = 1.0f / (colours.count-1);
CGFloat * locations = (CGFloat *)malloc((int)colours.count*sizeof(CGFloat));
CFMutableArrayRef mref = CFArrayCreateMutable(kCFAllocatorDefault, 0, &kCFTypeArrayCallBacks);

//2. go through the colours, creating cgColors and locations
for (int n = 0; n < colours.count; n++){
    CFArrayAppendValue(mref, (id)[colours[n] CGColor]);
    locations[n]=(n*increment);
}

//3. create gradient
CGContextRef ref = UIGraphicsGetCurrentContext();
CGColorSpaceRef spaceRef = CGColorSpaceCreateDeviceRGB();
CGGradientRef gradientRef = CGGradientCreateWithColors(spaceRef, mref, locations);

CGContextDrawLinearGradient(ref, gradientRef, start, end, kCGGradientDrawsAfterEndLocation);
free(locations);
CFRelease(mref);
CGColorSpaceRelease(spaceRef);
CGGradientRelease(gradientRef);
}

-(NSDictionary *)pointsForAngle:(float)angle width:(float)width height:(float)height{
    
    float n = 0.5f;
    
    CGPoint start = CGPointZero;
    CGPoint end = CGPointZero;
    
    if (angle >= 315 || angle < 45){
        
        start = CGPointMake(n * [self tanThis:angle] + n, 0);
        end = CGPointMake(n * [self tanThis:-angle] + n, 1);
        
    } else if (angle >= 45 && angle < 135){
        
        start = CGPointMake(0, n * [self tanThis:angle-90] + n);
        end = CGPointMake(1, n * [self tanThis:-angle-90] + n);
        
    } else if (angle >= 135 && angle < 225){
        
        start = CGPointMake(n * [self tanThis:-angle] + n, 1);
        end = CGPointMake(n * [self tanThis:angle] + n, 0);
        
    } else if (angle >= 225 && angle < 315){
        
        start = CGPointMake(1, n * [self tanThis:-angle-90] + n);
        end = CGPointMake(0, n * [self tanThis:angle-90] + n);

    }
    
    start = CGPointMake(start.x * width, start.y * height);
    end = CGPointMake(end.x * width, end.y * height);
    return @{@"start":@(start), @"end":@(end)};
    
}
-(float)tanThis:(float)angle{
    return tan(angle * M_PI / 180);
}