Iphone 通过向现有UIImage添加阴影来创建新UIImage

我看了一下这个问题：

但被接受的答案对我来说并不适用

我要做的是拍摄一个UIImage并向其添加一个阴影，然后返回一个全新的UIImage、阴影和所有内容

这就是我正在尝试的：

- (UIImage*)imageWithShadow {

    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef shadowContext = CGBitmapContextCreate(NULL, self.size.width, self.size.height + 1, CGImageGetBitsPerComponent(self.CGImage), 0, 
                                                 colourSpace, kCGImageAlphaPremultipliedLast);
    CGColorSpaceRelease(colourSpace);

    CGContextSetShadow(shadowContext, CGSizeMake(0, -1), 1);
    CGContextDrawImage(shadowContext, CGRectMake(0, 0, self.size.width, self.size.height), self.CGImage);

    CGImageRef shadowedCGImage = CGBitmapContextCreateImage(shadowContext);
    CGContextRelease(shadowContext);

    UIImage * shadowedImage = [UIImage imageWithCGImage:shadowedCGImage];
    CGImageRelease(shadowedCGImage);

    return shadowedImage;
}

结果是，我得到的图像与之前通过这种方法得到的图像完全相同

---

我这样做是正确的，还是有明显的遗漏？

您的代码有几个问题：

• 目标图像太小。确保有足够的地方画阴影
• 考虑使用

  CGContextSetShadowWithColor

  来定义阴影及其颜色
• 不要忘记坐标系是翻转的，所以原点是左下角，而不是左上角

通过解决这些问题，应该画出阴影

- (UIImage*)imageWithShadow {
    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef shadowContext = CGBitmapContextCreate(NULL, self.size.width + 10, self.size.height + 10, CGImageGetBitsPerComponent(self.CGImage), 0, 
                                             colourSpace, kCGImageAlphaPremultipliedLast);
    CGColorSpaceRelease(colourSpace);

    CGContextSetShadowWithColor(shadowContext, CGSizeMake(5, -5), 5, [UIColor blackColor].CGColor);
    CGContextDrawImage(shadowContext, CGRectMake(0, 10, self.size.width, self.size.height), self.CGImage);

    CGImageRef shadowedCGImage = CGBitmapContextCreateImage(shadowContext);
    CGContextRelease(shadowContext);

    UIImage * shadowedImage = [UIImage imageWithCGImage:shadowedCGImage];
    CGImageRelease(shadowedCGImage);

    return shadowedImage;
}

---

我需要一个方法，可以接受UIImage作为参数，并返回一个稍大的带有阴影的UIImage。这里的帖子对我很有帮助，下面是我的方法。 返回的图像在每一侧都有一个中心5px阴影

+(UIImage*)imageWithShadowForImage:(UIImage *)initialImage {

CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef shadowContext = CGBitmapContextCreate(NULL, initialImage.size.width + 10, initialImage.size.height + 10, CGImageGetBitsPerComponent(initialImage.CGImage), 0, colourSpace, kCGImageAlphaPremultipliedLast);
CGColorSpaceRelease(colourSpace);

CGContextSetShadowWithColor(shadowContext, CGSizeMake(0,0), 5, [UIColor blackColor].CGColor);
CGContextDrawImage(shadowContext, CGRectMake(5, 5, initialImage.size.width, initialImage.size.height), initialImage.CGImage);

CGImageRef shadowedCGImage = CGBitmapContextCreateImage(shadowContext);
CGContextRelease(shadowContext);

UIImage * shadowedImage = [UIImage imageWithCGImage:shadowedCGImage];
CGImageRelease(shadowedCGImage);

return shadowedImage;
}

---

我需要一个更大的阴影。这里是我的答案的变体，它允许自定义阴影大小而没有偏移

    - (UIImage*)imageWithShadow:(UIImage*)originalImage BlurSize:(float)blurSize {

    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef shadowContext = CGBitmapContextCreate(NULL, originalImage.size.width + (blurSize*2), originalImage.size.height + (blurSize*2), CGImageGetBitsPerComponent(originalImage.CGImage), 0, colourSpace, kCGImageAlphaPremultipliedLast);
    CGColorSpaceRelease(colourSpace);

    CGContextSetShadowWithColor(shadowContext, CGSizeMake(0, 0), blurSize, [UIColor blackColor].CGColor);
    CGContextDrawImage(shadowContext, CGRectMake(blurSize, blurSize, originalImage.size.width, originalImage.size.height), originalImage.CGImage);

    CGImageRef shadowedCGImage = CGBitmapContextCreateImage(shadowContext);
    CGContextRelease(shadowContext);

    UIImage * shadowedImage = [UIImage imageWithCGImage:shadowedCGImage];
    CGImageRelease(shadowedCGImage);

    return shadowedImage;
}

像这样使用它：

UIImage *shadowedImage = [self imageWithShadow:myImage BlurSize:30.0f];

---

要使图像成为本例中的

CGImage

，请尝试

self.shadowImage.CGImage

iOS8/Swift版本（作为UIImage的扩展）：

（由Laurent Etiemble和capikaw的答案转换而来）

编辑2016/10/31：转换为Swift 3，并删除所有不必要的内容

用法：

let sourceImage: UIImage(named: "some image")
let shadowImage = sourceImage.addShadow()

---

GK100在Swift 2/iOS9中的回答

func addShadow(blurSize: CGFloat = 6.0) -> UIImage {

    let data : UnsafeMutablePointer<Void> = nil
    let colorSpace:CGColorSpace = CGColorSpaceCreateDeviceRGB()!
    let bitmapInfo : CGBitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedLast.rawValue)

    let myColorValues:[CGFloat] = [0.0, 0.0, 0.0, 0.8]
    let myColor = CGColorCreate(colorSpace, myColorValues)

    let shadowContext : CGContextRef = CGBitmapContextCreate(data, Int(self.size.width + blurSize), Int(self.size.height + blurSize), CGImageGetBitsPerComponent(self.CGImage), 0, colorSpace, bitmapInfo.rawValue)!

    CGContextSetShadowWithColor(shadowContext, CGSize(width: blurSize/2,height: -blurSize/2),  blurSize, myColor)
    CGContextDrawImage(shadowContext, CGRect(x: 0, y: blurSize, width: self.size.width, height: self.size.height), self.CGImage)

    let shadowedCGImage : CGImageRef = CGBitmapContextCreateImage(shadowContext)!
    let shadowedImage : UIImage = UIImage(CGImage: shadowedCGImage)

    return shadowedImage
}

func addShadow（模糊大小：CGFloat=6.0）->UIImage{
let数据：UnsafeMutablePointer=nil
让colorSpace:CGColorSpace=CGColorSpace创建设备GB（）！
让bitmapInfo:CGBitmapInfo=CGBitmapInfo（rawValue:CGImageAlphaInfo.PremultipledLast.rawValue）
让myColorValues:[CGFloat]=[0.0,0.0,0.0,0.8]
让myColor=CGColorCreate（颜色空间，mycolorValue）
让shadowContext:CGContextRef=CGBitmapContextCreate（数据，Int（self.size.width+blurSize），Int（self.size.height+blurSize），CGImageGetBitsPerComponent（self.CGImage），0，颜色空间，bitmapInfo.rawValue）！
CGContextSetShadowWithColor（阴影上下文，CGSize（宽度：blurSize/2，高度：-blurSize/2），blurSize，myColor）
CGContextDrawImage（shadowContext，CGRect（x:0，y:blurSize，width:self.size.width，height:self.size.height），self.CGImage）
让shadowedCGImage:CGImageRef=CGBitmapContextCreateImage（shadowContext）！
让shadoweImage:UIImage=UIImage（CGImage:shadowedCGImage）
返回阴影图像
}

我在图像上绘制阴影的方法。它具有自定义阴影参数，并以正确的大小和屏幕比例渲染图像。应该在UIImage扩展中实现。（Swift 3）

---

在尝试使用这里的其他一些示例时，我注意到它们似乎要么硬编码偏移和模糊，要么在调整输出大小和定位时没有正确考虑它们

以下代码解决了这些问题（它基于Igor Kulagin的原始工作）：

---

完美的我实际上是在高度上加1来绘制阴影，但是其他的东西（设置阴影，翻转坐标系）是非常重要的。这段代码将在哪里实现，以及如何调用它来为图像添加阴影？该方法假设该类可以提供CGImage及其尺寸。您可以更改此方法以获取参数（CGImage和CGSize）。如何将UIImage转换为CGImage？@user403015:使用UIImage的CGImage属性。如果UIImage将显示在UIImageView中，您也可以向视图添加阴影效果。看见

func addShadow(blurSize: CGFloat = 6.0) -> UIImage {

    let data : UnsafeMutablePointer<Void> = nil
    let colorSpace:CGColorSpace = CGColorSpaceCreateDeviceRGB()!
    let bitmapInfo : CGBitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedLast.rawValue)

    let myColorValues:[CGFloat] = [0.0, 0.0, 0.0, 0.8]
    let myColor = CGColorCreate(colorSpace, myColorValues)

    let shadowContext : CGContextRef = CGBitmapContextCreate(data, Int(self.size.width + blurSize), Int(self.size.height + blurSize), CGImageGetBitsPerComponent(self.CGImage), 0, colorSpace, bitmapInfo.rawValue)!

    CGContextSetShadowWithColor(shadowContext, CGSize(width: blurSize/2,height: -blurSize/2),  blurSize, myColor)
    CGContextDrawImage(shadowContext, CGRect(x: 0, y: blurSize, width: self.size.width, height: self.size.height), self.CGImage)

    let shadowedCGImage : CGImageRef = CGBitmapContextCreateImage(shadowContext)!
    let shadowedImage : UIImage = UIImage(CGImage: shadowedCGImage)

    return shadowedImage
}

func addingShadow(blur: CGFloat = 1, shadowColor: UIColor = UIColor(white: 0, alpha: 1), offset: CGSize = CGSize(width: 1, height: 1) ) -> UIImage {

    UIGraphicsBeginImageContextWithOptions(CGSize(width: size.width + 2 * blur, height: size.height + 2 * blur), false, 0)
    let context = UIGraphicsGetCurrentContext()!

    context.setShadow(offset: offset, blur: blur, color: shadowColor.cgColor)
    draw(in: CGRect(x: blur - offset.width / 2, y: blur - offset.height / 2, width: size.width, height: size.height))
    let image = UIGraphicsGetImageFromCurrentImageContext()!

    UIGraphicsEndImageContext()

    return image
}

extension UIImage {
    /// Returns a new image with the specified shadow properties.
    /// This will increase the size of the image to fit the shadow and the original image.
    func withShadow(blur: CGFloat = 6, offset: CGSize = .zero, color: UIColor = UIColor(white: 0, alpha: 0.8)) -> UIImage {

        let shadowRect = CGRect(
            x: offset.width - blur,
            y: offset.height - blur,
            width: size.width + blur * 2,
            height: size.height + blur * 2
        )
        
        UIGraphicsBeginImageContextWithOptions(
            CGSize(
                width: max(shadowRect.maxX, size.width) - min(shadowRect.minX, 0),
                height: max(shadowRect.maxY, size.height) - min(shadowRect.minY, 0)
            ),
            false, 0
        )
        
        let context = UIGraphicsGetCurrentContext()!

        context.setShadow(
            offset: offset,
            blur: blur,
            color: color.cgColor
        )
        
        draw(
            in: CGRect(
                x: max(0, -shadowRect.origin.x),
                y: max(0, -shadowRect.origin.y),
                width: size.width,
                height: size.height
            )
        )
        let image = UIGraphicsGetImageFromCurrentImageContext()!
        
        UIGraphicsEndImageContext()
        return image
    }
}