我正在尝试使用 CoreGraphic 将渐变应用于 UIImage;然而,我得到的结果不是很好。我想在图像底部创建一个黑色到透明的渐变,以便为我放置一些文本创建对比度。然而,我能够实现的渐变与图像不能很好地融合;你可以清楚地看到中心的分离。我正在寻找的结果就像这个应用程序:http://capptivate.co/2014/02/17/yummly-3/ http://capptivate.co/2014/02/17/yummly-3/我应该如何应用渐变来实现这一目标? (我必须将其应用于大量图像)。
我的结果:
这是我的代码:
func imageWithGradient(img:UIImage!) -> UIImage{
UIGraphicsBeginImageContext(img.size)
var context = UIGraphicsGetCurrentContext()
img.drawAtPoint(CGPointMake(0, 0))
let colorSpace = CGColorSpaceCreateDeviceRGB()
let locations:[CGFloat] = [0.50, 1.0]
//1 = opaque
//0 = transparent
let bottom = UIColor(red: 0, green: 0, blue: 0, alpha: 0.5).CGColor
let top = UIColor(red: 0, green: 0, blue: 0, alpha: 0).CGColor
let gradient = CGGradientCreateWithColors(colorSpace,
[top, bottom], locations)
let startPoint = CGPointMake(img.size.width/2, 0)
let endPoint = CGPointMake(img.size.width/2, img.size.height)
CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0)
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return image
}
SWIFT 3
func imageWithGradient(img:UIImage!) -> UIImage {
UIGraphicsBeginImageContext(img.size)
let context = UIGraphicsGetCurrentContext()
img.draw(at: CGPoint(x: 0, y: 0))
let colorSpace = CGColorSpaceCreateDeviceRGB()
let locations:[CGFloat] = [0.0, 1.0]
let bottom = UIColor(red: 0, green: 0, blue: 0, alpha: 0.5).cgColor
let top = UIColor(red: 0, green: 0, blue: 0, alpha: 0).cgColor
let colors = [top, bottom] as CFArray
let gradient = CGGradient(colorsSpace: colorSpace, colors: colors, locations: locations)
let startPoint = CGPoint(x: img.size.width/2, y: 0)
let endPoint = CGPoint(x: img.size.width/2, y: img.size.height)
context!.drawLinearGradient(gradient!, start: startPoint, end: endPoint, options: CGGradientDrawingOptions(rawValue: UInt32(0)))
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return image!
}
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