通过向现有UIImage添加阴影来创建新的UIImage

Question

我看了一下这个问题:UIImage Shadow Trouble

但接受的答案对我不起作用.

我正在尝试做的是采用UIImage并为其添加阴影,然后返回一个全新的UIImage,阴影和所有.

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;
}

结果是我得到了与之前通过此方法完全相同的图像.

我这样做是正确的,或者有什么明显的东西我不见了？

Answer 1

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.
• 不要忘记坐标系被翻转,因此原点是左下角,而不是左上角.

通过解决这些问题,应该绘制阴影.

- (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;
}

Answer 2

iOS8/Swift版本(作为UIImage的扩展):

extension UIImage {

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

        let shadowColor = UIColor(white:0.0, alpha:0.8).cgColor

        let context = CGContext(data: nil,
                                width: Int(self.size.width + blurSize),
                                height: Int(self.size.height + blurSize),
                                bitsPerComponent: self.cgImage!.bitsPerComponent,
                                bytesPerRow: 0,
                                space: CGColorSpaceCreateDeviceRGB(),
                                bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)!

        context.setShadow(offset: CGSize(width: blurSize/2,height: -blurSize/2),
                          blur: blurSize,
                          color: shadowColor)
        context.draw(self.cgImage!,
                     in: CGRect(x: 0, y: blurSize, width: self.size.width, height: self.size.height),
                     byTiling:false)

        return UIImage(cgImage: context.makeImage()!)
    }
}

(由Laurent Etiemble转换为&capikaw答案)

编辑 2016/10/31:转换为Swift 3,并删除所有不必要的东西

用法:

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

Answer 3

我需要一个接受UIImage作为参数的方法,并返回一个带阴影的稍大的UIImage.这里的帖子对我很有帮助,所以这是我的方法.返回的图像每侧有一个居中的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;
}

Answer 4

我的 UIImages 需要更大的阴影。这是我的答案变体，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];

Answer 5

在尝试在这里使用其他一些示例时，我注意到它们似乎要么对偏移和模糊进行硬编码，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 的原创作品）：

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
    }
}