iOS中的模糊效果

App设计时往往会用到一些模糊效果。iOS目前已提供一些模糊API可以让我们方便是使用。一种是使用Core Image，另一种是使用Accelerate.Framework中的vImage API。

使用Core Image进行模糊

Core Image很早在Mac系统中得到应用，后来这个Framework也开始应用到iOS，不过直到iOS6.0才开始支持模糊。这个API调用起来很方便简洁。

- (UIImage *)blurryImage:(UIImage *)image 
           withBlurLevel:(CGFloat)blur {
    CIImage *inputImage = [CIImage imageWithCGImage:image.CGImage];
    CIFilter *filter = [CIFilter filterWithName:@"CIGaussianBlur"
                         keysAndValues:kCIInputImageKey, inputImage,
                                       @"inputRadius", @(blur), 
                                       nil];
     
    CIImage *outputImage = filter.outputImage;
     
    CGImageRef outImage = [self.context createCGImage:outputImage 
                                   fromRect:[outputImage extent]];
    return [UIImage imageWithCGImage:outImage];
}

使用vImage API进行模糊

iOS5.0中新增了vImage API可以使用，它属于Accelerate.Framework，所以如果你要使用它要在工程中加入这个Framework。模糊算法使用的是vImageBoxConvolve_ARGB8888这个函数。

- (UIImage *)blurryImage:(UIImage *)image withBlurLevel:(CGFloat)blur {
    if (blur < 0.f || blur > 1.f) {
        blur = 0.5f;
    }
    int boxSize = (int)(blur * 100);
    boxSize = boxSize - (boxSize % 2) + 1;
     
    CGImageRef img = image.CGImage;
     
    vImage_Buffer inBuffer, outBuffer;
    vImage_Error error;
     
    void *pixelBuffer;
     
    CGDataProviderRef inProvider = CGImageGetDataProvider(img);
    CFDataRef inBitmapData = CGDataProviderCopyData(inProvider);
     
    inBuffer.width = CGImageGetWidth(img);
    inBuffer.height = CGImageGetHeight(img);
    inBuffer.rowBytes = CGImageGetBytesPerRow(img);
     
    inBuffer.data = (void*)CFDataGetBytePtr(inBitmapData);
     
    pixelBuffer = malloc(CGImageGetBytesPerRow(img) * 
                         CGImageGetHeight(img));
     
    if(pixelBuffer == NULL)
        NSLog(@"No pixelbuffer");
     
    outBuffer.data = pixelBuffer;
    outBuffer.width = CGImageGetWidth(img);
    outBuffer.height = CGImageGetHeight(img);
    outBuffer.rowBytes = CGImageGetBytesPerRow(img);
     
    error = vImageBoxConvolve_ARGB8888(&inBuffer, 
                                       &outBuffer, 
                                       NULL, 
                                       0, 
                                       0, 
                                       boxSize, 
                                       boxSize, 
                                       NULL, 
                                       kvImageEdgeExtend);
     
     
    if (error) {
        NSLog(@"error from convolution %ld", error);
    }
     
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef ctx = CGBitmapContextCreate(
                                    outBuffer.data,
                                    outBuffer.width,
                                    outBuffer.height,
                                    8,
                                    outBuffer.rowBytes,
                                    colorSpace,
                                    kCGImageAlphaNoneSkipLast);
    CGImageRef imageRef = CGBitmapContextCreateImage (ctx);
    UIImage *returnImage = [UIImage imageWithCGImage:imageRef];
     
    //clean up
    CGContextRelease(ctx);
    CGColorSpaceRelease(colorSpace);
     
    free(pixelBuffer);
    CFRelease(inBitmapData);
     
    CGColorSpaceRelease(colorSpace);
    CGImageRelease(imageRef);
     
    return returnImage;
}