如何使用"from-color"和"to-color"创建具有垂直渐变的UIImage

Question

如何使用渐变色创建新图像,使用"从颜色"和"到颜色"？

Answer 1

首先,您需要创建所需大小的图形上下文:

CGSize size = CGSizeMake(width, height);
UIGraphicsBeginImageContextWithOptions(size, NO, 0);
CGContextRef context = UIGraphicsGetCurrentContext();

创建颜色空间:

CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();

现在创建渐变:

size_t gradientNumberOfLocations = 2;
CGFloat gradientLocations[2] = { 0.0, 1.0 };
CGFloat gradientComponents[8] = { r0, g0, b0, a0,     // Start color
                                  r1, g1, b1, a1, };  // End color

CGGradientRef gradient = CGGradientCreateWithColorComponents (colorspace, gradientComponents, gradientLocations, gradientNumberOfLocations);

使用渐变填充上下文 - 这假定为垂直渐变:

CGContextDrawLinearGradient(context, gradient, CGPointMake(0, 0), CGPointMake(0, size.height), 0);

现在您可以从上下文创建图像:

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

最后释放渐变,颜色空间和上下文:

CGGradientRelease(gradient);
CGColorSpaceRelease(colorspace);
UIGraphicsEndImageContext();

Answer 2

一个更简单的答案,使用CAGradientLayer.

CGSize size = CGSizeMake(width, height);
CAGradientLayer *layer = [CAGradientLayer layer];
layer.frame = CGRectMake(0, 0, size.width, size.height);
layer.colors = @[(__bridge id)[UIColor blackColor].CGColor,  // start color
                 (__bridge id)[UIColor whiteColor].CGColor]; // end color

UIGraphicsBeginImageContext(size);
@try {
  [layer renderInContext:UIGraphicsGetCurrentContext()];
  UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
} @finally {
  UIGraphicsEndImageContext();
}

Answer 3

我认为,它更加开心

斯威夫特3

struct GradientPoint {
   var location: CGFloat
   var color: UIColor
}



extension UIImage {
convenience init?(size: CGSize, gradientPoints: [GradientPoint]) {
    UIGraphicsBeginImageContextWithOptions(size, false, UIScreen.main.scale)

    guard let context = UIGraphicsGetCurrentContext() else { return nil }       // If the size is zero, the context will be nil.
    guard let gradient = CGGradient(colorSpace: CGColorSpaceCreateDeviceRGB(), colorComponents: gradientPoints.flatMap { $0.color.cgColor.components }.flatMap { $0 }, locations: gradientPoints.map { $0.location }, count: gradientPoints.count) else {
        return nil
    }

    context.drawLinearGradient(gradient, start: CGPoint.zero, end: CGPoint(x: 0, y: size.height), options: CGGradientDrawingOptions())
    guard let image = UIGraphicsGetImageFromCurrentImageContext()?.cgImage else { return nil }
    self.init(cgImage: image)
    defer { UIGraphicsEndImageContext() }
}
}


extension UIImageView {
   func gradated(gradientPoints: [GradientPoint]) {
    let gradientMaskLayer       = CAGradientLayer()
    gradientMaskLayer.frame     = frame
    gradientMaskLayer.colors    = gradientPoints.map { $0.color.cgColor }
    gradientMaskLayer.locations = gradientPoints.map { $0.location as NSNumber }
    self.layer.insertSublayer(gradientMaskLayer, at: 0)
}
}

像这样使用,

let points = [GradientPoint(location: 0, color: #colorLiteral(red: 0.7450980544, green: 0.1568627506, blue: 0.07450980693, alpha: 0.2530534771)), GradientPoint(location: 0.2, color: #colorLiteral(red: 0.9686274529, green: 0.78039217, blue: 0.3450980484, alpha: 0.5028884243)), GradientPoint(location: 0.4, color: #colorLiteral(red: 0.721568644, green: 0.8862745166, blue: 0.5921568871, alpha: 0.3388534331)),
          GradientPoint(location: 0.6, color: #colorLiteral(red: 0.2588235438, green: 0.7568627596, blue: 0.9686274529, alpha: 0.3458681778)), GradientPoint(location: 0.8, color: #colorLiteral(red: 0.2196078449, green: 0.007843137719, blue: 0.8549019694, alpha: 0.3851232394))]

UIImage(size: CGSize(width: 300, height: 300), gradientPoints: points)


let veniceImageView = UIImageView(image: #imageLiteral(resourceName: "venice-italy.jpg"))
veniceImageView.gradated(gradientPoints: points)

我测试了swift 3.检查屏幕截图.

Answer 4

更新到Swift 3

我UIImage为Swift 编写了扩展,但你也可以在Objective-C中使用它:

import UIKit

private let ChannelDivider: CGFloat = 255

public class RGBA: NSObject {
    var red: CGFloat
    var green: CGFloat
    var blue: CGFloat
    var alpha: CGFloat

    init(red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) {
        self.red = red
        self.green = green
        self.blue = blue
        self.alpha = alpha
    }

    init(intRed: Int, green: Int, blue: Int, alpha: Int) {
        self.red = CGFloat(intRed)/ChannelDivider
        self.green = CGFloat(green)/ChannelDivider
        self.blue = CGFloat(blue)/ChannelDivider
        self.alpha = CGFloat(alpha)/ChannelDivider
    }
}

public class Grayscale: NSObject {
    var white: CGFloat
    var alpha: CGFloat

    init(white: CGFloat, alpha: CGFloat) {
        self.white = white
        self.alpha = alpha
    }
}

public class GradientPoint<C>: NSObject {
    var location: CGFloat
    var color: C

    init(location: CGFloat, color: C) {
        self.location = location
        self.color = color
    }
}

extension UIImage {

    public class func image(withGradientPoints gradientPoints: [GradientPoint<[CGFloat]>], colorSpace: CGColorSpace, size: CGSize) -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(size, false, 0);
        guard
            let context = UIGraphicsGetCurrentContext(),
            let gradient = CGGradient(colorSpace: colorSpace,
                                      colorComponents: gradientPoints.flatMap { $0.color },
                                      locations: gradientPoints.map { $0.location }, count: gradientPoints.count) else {
                                        return nil
        }

        context.drawLinearGradient(gradient, start: CGPoint.zero, end: CGPoint(x: 0, y: size.height), options: CGGradientDrawingOptions())
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return image
    }

    public class func image(withRGBAGradientPoints gradientPoints: [GradientPoint<RGBA>], size: CGSize) -> UIImage? {
        return image(withGradientPoints: gradientPoints.map {
            GradientPoint(location: $0.location, color: [$0.color.red, $0.color.green, $0.color.blue, $0.color.alpha])
        }, colorSpace: CGColorSpaceCreateDeviceRGB(), size: size)
    }

    public class func image(withRGBAGradientColors gradientColors: [CGFloat: RGBA], size: CGSize) -> UIImage? {
        return image(withRGBAGradientPoints: gradientColors.map {  GradientPoint(location: $0, color: $1)}, size: size)
    }

    public class func image(withGrayscaleGradientPoints gradientPoints: [GradientPoint<Grayscale>], size: CGSize) -> UIImage? {
        return image(withGradientPoints: gradientPoints.map {
            GradientPoint(location: $0.location, color: [$0.color.white, $0.color.alpha]) },
                     colorSpace: CGColorSpaceCreateDeviceGray(), size: size)
    }

    public class func image(withGrayscaleGradientColors gradientColors: [CGFloat: Grayscale], size: CGSize) -> UIImage? {
        return image(withGrayscaleGradientPoints: gradientColors.map { GradientPoint(location: $0, color: $1) }, size: size)
    }
}

您可以使用RGBA颜色创建渐变图像:

// Objective-C
RGBA *startColor = [[RGBA alloc] initWithRed:1 green:0 blue:0 alpha:1];
RGBA *endColor = [[RGBA alloc] initWithIntRed:0 green:255 blue:0 alpha:255];
UIImage *gradientImage = [UIImage imageWithRGBAGradient: @{ @0: startColor, @1: endColor} size: CGSizeMake(32, 64)];

// Swift
let startColor = RGBA(red: 1, green: 0, blue: 0, alpha: 1)
let endColor = RGBA(intRed: 0, green: 255, blue: 0, alpha: 255)
let gradientImage = UIImage.image(withRGBAGradientPoints: [0: startColor, 1: endColor], size: CGSizeMake(32, 64))

和灰度颜色:

// Objective-C
Grayscale *startColor = [[Grayscale alloc] initWithWhite:1 alpha:1];
Grayscale *endColor = [[Grayscale alloc] initWithWhite:0 alpha: 0.5];
UIImage *gradientImage = [UIImage imageWithGrayscaleGradient: @{ @0: startColor, @1: endColor} size: CGSizeMake(32, 64)];

// Swift
let startColor = Grayscale(white: 1, alpha: 1)
let endColor = Grayscale(white:0, alpha: 0.5)
let gradientImage = UIImage.image(withGrayscaleGradientPoints: [0: startColor, 1: endColor], size: CGSizeMake(32, 64))

如果你不打算使用此代码从Objective-C的比你可以删除NSObject从继承RGBA,Grayscale和GradientPoint.