iOS - 绘制渐变 - Swift

Question

我正在尝试绘制 UILabel 的渐变，但它只绘制我看不到文本的颜色。我从这里看到了代码StackOverflow

我的修改:

extension String{
    func gradient(x:CGFloat,y:CGFloat, fontSize:CGFloat)->UIImage{
        let font:UIFont = UIFont.systemFontOfSize(fontSize)
        let name:String = NSFontAttributeName
        let textSize: CGSize = self.sizeWithAttributes([name:font])
        let width:CGFloat = textSize.width         // max 1024 due to Core Graphics limitations
        let height:CGFloat = textSize.height       // max 1024 due to Core Graphics limitations
        UIGraphicsBeginImageContext(CGSizeMake(width, height))
        let context = UIGraphicsGetCurrentContext()
        UIGraphicsPushContext(context!)
        //draw gradient
        let glossGradient:CGGradientRef?
        let rgbColorspace:CGColorSpaceRef?
        let num_locations:size_t = 2
        let locations:[CGFloat] = [ 0.0, 1.0 ]
        let components:[CGFloat] = [(202 / 255.0), (197 / 255.0), (52 / 255.0), 1.0,  // Start color
            (253 / 255.0), (248 / 255.0), (101 / 255.0), 1.0] // End color
        rgbColorspace = CGColorSpaceCreateDeviceRGB()
        glossGradient = CGGradientCreateWithColorComponents(rgbColorspace, components, locations, num_locations)
        let topCenter = CGPointMake(0, 0);
        let bottomCenter = CGPointMake(0, textSize.height);
        CGContextDrawLinearGradient(context, glossGradient, topCenter, bottomCenter, CGGradientDrawingOptions.DrawsBeforeStartLocation)
        UIGraphicsPopContext()
        let gradientImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return  gradientImage
    }
}

以及imageView的设置

    self.timeLeftIV = UIImageView(frame: CGRectMake(self.pyramidFakeView.frame.origin.x/2-25,0, 100,20))
    self.timeLeftIV.image = "59:48".gradient(timeLeftIV.frame.origin.x, y: timeLeftIV.frame.origin.y, fontSize: 6.0)

代码的结果:

Answer 1

有一种更简单的方法来获取 UIImage 形式的渐变。您可以使用CAGradientLayer。例如:

func yellowGradientImage(bounds:CGRect) -> UIImage
{
    let gradientLayer = CAGradientLayer()
    gradientLayer.colors = [UIColor(red: (202 / 255.0), green: (197 / 255.0), blue: (52 / 255.0), alpha: 1.0).CGColor, UIColor(red: (253 / 255.0), green: (248 / 255.0), blue: (101 / 255.0), alpha: 1.0).CGColor]
    gradientLayer.bounds = bounds
    UIGraphicsBeginImageContextWithOptions(gradientLayer.bounds.size, true, 0.0)
    let context = UIGraphicsGetCurrentContext()
    gradientLayer.renderInContext(context!)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image
}

要将渐变应用于文本，您接下来需要使用 UIColor(patternImage: ...) 作为 textColor 返回的图像。例如:

let label = UILabel()
label.font = UIFont.systemFontOfSize(150.0)
label.text = "HELLO WORLD"
label.sizeToFit()

let image = yellowGradientImage(label.bounds)
label.textColor = UIColor(patternImage: image)

结果是:

swift 3.0:

func yellowGradientImage(bounds:CGRect) -> UIImage
{
    let gradientLayer = CAGradientLayer()
    gradientLayer.colors = [UIColor(red: (202 / 255.0), green: (197 / 255.0), blue: (52 / 255.0), alpha: 1.0).cgColor, UIColor(red: (253 / 255.0), green: (248 / 255.0), blue: (101 / 255.0), alpha: 1.0).cgColor]
    gradientLayer.bounds = bounds
    UIGraphicsBeginImageContextWithOptions(gradientLayer.bounds.size, true, 0.0)
    let context = UIGraphicsGetCurrentContext()
    gradientLayer.render(in: context!)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image!
}

let label = UILabel()
label.font = UIFont.systemFont(ofSize: 150.0)
label.text = "HELLO WORLD"
label.sizeToFit()

let image = yellowGradientImage(bounds: label.bounds)
label.textColor = UIColor(patternImage: image)