如何在iphone上的新图像上渲染径向渐变

只是想知道如何在新的UIImage（iphone）上渲染径向渐变（点>圆）。 我看到了以下情况：

这让我觉得我需要使用CGShadingRef或CGGradientRef，并使用UIImage的“imageWithCGImage”构造函数从CG*转换为UIImage。。。但我不知道怎么做

非常感谢您的任何建议

您应该在与链接部分相同的文档中阅读。所有绘图都发生在图形上下文中。如果要创建具有径向渐变、线性渐变或其他任何内容的图像，则需要：

• 使用为图像创建图形上下文
• 执行希望在图像中显示的任何图形
• 调用以从上下文中获取图像。这将为您提供一个UIImage，因此无需从CGImage转换
• 调用以清理上下文

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好的，这是工作解决方案的要点，如果我遗漏了什么，请告诉我（例如释放句柄/引用）
也在我的博客上发布：

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您还可以在iOS5+中使用CoreImage并使用Vignette过滤器

- (UIImage *)vignetteImageOfSize:(CGSize)size withImage:(UIImage *)image {  
    UIGraphicsBeginImageContextWithOptions(size, YES, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
    CGContextFillRect(context, CGRectMake(0.0, 0.0, size.width, size.height));

    CIImage *coreImage = [CIImage imageWithCGImage:image.CGImage];
    CGPoint origin = [coreImage extent].origin;
    CGAffineTransform translation =
    CGAffineTransformMakeTranslation(-origin.x, -origin.y);
    coreImage = [coreImage imageByApplyingTransform:translation];

    CIFilter *vignette = [[CIFilter filterWithName:@"CIVignette"] retain];
    [vignette setValue:@1.5 forKey:@"inputRadius"];
    [vignette setValue:@1.5 forKey:@"inputIntensity"];
    [vignette setValue:coreImage forKey:@"inputImage"];

    UIImage *vignetteImage = [UIImage imageWithCIImage:vignette.outputImage];
    [vignette release];

    CGRect imageFrame = CGRectMake(0.0, 0.0, size.width, size.height);
    [image drawInRect:imageFrame];
    UIImage *renderedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return renderedImage;
}

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我在这里编写了这个简化的方法（例如，将其放入UIImage类别中）
示例用法：

// resulting image size 128x128 px
UIImage* myRadialImage = [UIImage radialGradientImageWithRadius:128.f StartColor:[UIColor greenColor] EndColor:nil ApplyScreenScale:NO]; 

// resulting image size 256x256 px on normal retina display, or 384x384 on iPhone 6 or gre 
UIImage* myRadialImage = [UIImage radialGradientImageWithRadius:128.f StartColor:[UIColor greenColor] EndColor:[UIColor redColor] ApplyScreenScale:YES]; 

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希望有用
为UIView设置径向渐变颜色
对于梯度

extension UIColor {
func colorWithRadialGradient(frame: CGRect, colors: [UIColor]) -> UIColor {
    if frame.width != 0.0 && frame.height != 0.0 {
        let backgroundGradientLayer = CAGradientLayer()
        backgroundGradientLayer.frame = frame
        let cgColors = colors.map({$0.cgColor})
        backgroundGradientLayer.colors = cgColors
        backgroundGradientLayer.type = kCAGradientLayerRadial
        backgroundGradientLayer.startPoint = CGPoint(x: 0.5, y: 0.1)
        UIGraphicsBeginImageContext(backgroundGradientLayer.bounds.size)
        backgroundGradientLayer.render(in: UIGraphicsGetCurrentContext()!)
        let backgroundColorImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return UIColor(patternImage: backgroundColorImage!)
    }
    return .clear
    }
}

（可选）对于外部阴影

extension UIView
{
func setGreenCircularShadow() {
    let greenGradient = [UIColor(red: 13/255.0, green: 160/255.0, blue: 110/255.0, alpha: 0.8),UIColor(red: 7/255.0, green: 200/255.0, blue: 128/255.0, alpha: 1.0),UIColor(red: 7/255.0, green: 200/255.0, blue: 128/255.0, alpha: 1.0), UIColor(red: 13/255.0, green: 160/255.0, blue: 110/255.0, alpha: 0.8)]
    self.backgroundColor        = UIColor().colorWithRadialGradient(frame: self.bounds, colors: greenGradient)
    self.layer.shadowColor      = UIColor(red: 7.0/255.0, green: 200.0/255.0, blue: 128.0/255.0, alpha: 1.0).cgColor
    self.layer.shadowOpacity    = 0.33
    self.layer.shadowOffset     = CGSize(width: 0, height: 5.0)
    self.layer.shadowRadius     = 10
    self.layer.shadowPath       = UIBezierPath(rect: self.bounds).cgPath
   }
}

设置为UIVIEW

view.layer.cornerRadius = 5.0
view.setGreenCircularShadow()

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但是图像应用在哪里？该方法的目标是什么？

extension UIView
{
func setGreenCircularShadow() {
    let greenGradient = [UIColor(red: 13/255.0, green: 160/255.0, blue: 110/255.0, alpha: 0.8),UIColor(red: 7/255.0, green: 200/255.0, blue: 128/255.0, alpha: 1.0),UIColor(red: 7/255.0, green: 200/255.0, blue: 128/255.0, alpha: 1.0), UIColor(red: 13/255.0, green: 160/255.0, blue: 110/255.0, alpha: 0.8)]
    self.backgroundColor        = UIColor().colorWithRadialGradient(frame: self.bounds, colors: greenGradient)
    self.layer.shadowColor      = UIColor(red: 7.0/255.0, green: 200.0/255.0, blue: 128.0/255.0, alpha: 1.0).cgColor
    self.layer.shadowOpacity    = 0.33
    self.layer.shadowOffset     = CGSize(width: 0, height: 5.0)
    self.layer.shadowRadius     = 10
    self.layer.shadowPath       = UIBezierPath(rect: self.bounds).cgPath
   }
}

view.layer.cornerRadius = 5.0
view.setGreenCircularShadow()