遇到一例案例，iOS 10.1.1 使用CIBlendWithAlphaMask 渲染生成马赛克涂抹效果时，没有渲染出来，改为GPU绘制后，倒就正常了。原因未知，暂且记录下解决方案。

已知问题机型：

iphone 7p   iOS 10.1.1
iphone 6sp  iOS 10.1.1
iphone 6        iOS 10.1.1
(iphone 5 iOS 10.1.1 没有问题)

原实现：

CIImage *resultImage = [[CIFilter filterWithName:@"CIBlendWithAlphaMask"
                                       keysAndValues:kCIInputImageKey, ciOutputImagePixellate,
                                                    kCIInputMaskImageKey, maskImage,
                                                    kCIInputBackgroundImageKey, ciInputImage, nil]
                            valueForKey:kCIOutputImageKey];

CIContext *ciContext = [CIContext contextWithOptions:nil];
CGImageRef cgImage = [ciContext createCGImage:resultImage fromRect:[resultImage extent]];

CGImageRef cgImage = [ciContext createCGImage:resultImage fromRect:[resultImage extent]];
    
// 获取UIImage
UIImage *filteredImage = [UIImage imageWithCGImage:cgImage];
CGImageRelease(cgImage);

修改后实现方案：

CIImage *resultImage = [[CIFilter filterWithName:@"CIBlendWithAlphaMask"
                                       keysAndValues:kCIInputImageKey, ciOutputImagePixellate,
                                                    kCIInputMaskImageKey, maskImage,
                                                    kCIInputBackgroundImageKey, ciInputImage, nil]
                            valueForKey:kCIOutputImageKey];
                            
EAGLContext *glContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];

CIContext *ciContext = [CIContext contextWithEAGLContext:glContext
                                                     options:@{kCIContextWorkingColorSpace : [NSNull null]}];
    
CGImageRef cgImage = [ciContext createCGImage:resultImage fromRect:[resultImage extent]];
    
// 获取UIImage
UIImage *filteredImage = [UIImage imageWithCGImage:cgImage];
CGImageRelease(cgImage);

附上图片部分马赛克的源码：

- (UIImage *)demoCoreImageFilter {
    
    UIImage *originImage = [UIImage imageNamed:@"facetest"];
    // 导入CIImage
    CIImage *ciInputImage = [[CIImage alloc] initWithImage:originImage];
    
    // 创建CIFilter
    CIFilter *filterPixellate = [CIFilter filterWithName:@"CIPixellate"];
    [filterPixellate setValue:ciInputImage forKey:kCIInputImageKey];
    [filterPixellate setDefaults];
    [filterPixellate setValue:@32 forKey:@"inputScale"];
    NSLog(@"filterPixellate : %@", filterPixellate.attributes);
    
    // 获取滤镜效果之后的CIImage
    CIImage *ciOutputImagePixellate = [filterPixellate valueForKey:kCIOutputImageKey];
    
    
    // 人脸识别
    CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeFace
                                              context:nil
                                              options:nil];
    NSArray *faceArray = [detector featuresInImage:ciInputImage options:nil];
    
    // Create a green circle to cover the rects that are returned.
    
    CIImage *maskImage = nil;
    
    for (CIFeature *f in faceArray) {
        CGFloat centerX = f.bounds.origin.x + f.bounds.size.width / 2.0;
        CGFloat centerY = f.bounds.origin.y + f.bounds.size.height / 2.0;
        CGFloat radius = MIN(f.bounds.size.width, f.bounds.size.height) / 1.5;
        CIFilter *radialGradient = [CIFilter filterWithName:@"CIRadialGradient" withInputParameters:@{
                                                                                                      @"inputRadius0": @(radius),
                                                                                                      @"inputRadius1": @(radius + 1.0f),
                                                                                                      @"inputColor0": [CIColor colorWithRed:0.0 green:1.0 blue:0.0 alpha:1.0],
                                                                                                      @"inputColor1": [CIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:0.0],
                                                                                                      kCIInputCenterKey: [CIVector vectorWithX:centerX Y:centerY],
                                                                                                      }];
        CIImage *circleImage = [radialGradient valueForKey:kCIOutputImageKey];
        if (nil == maskImage)
            maskImage = circleImage;
        else
            maskImage = [[CIFilter filterWithName:@"CISourceOverCompositing" withInputParameters:@{
                                                                                                   kCIInputImageKey: circleImage,
                                                                                                   kCIInputBackgroundImageKey: maskImage,
                                                                                                   }] valueForKey:kCIOutputImageKey];
    }
    
    CIImage *resultImage = [[CIFilter filterWithName:@"CIBlendWithAlphaMask"
                                       keysAndValues:kCIInputImageKey, ciOutputImagePixellate,
                                                    kCIInputMaskImageKey, maskImage,
                                                    kCIInputBackgroundImageKey, ciInputImage, nil]
                            valueForKey:kCIOutputImageKey];
    
    EAGLContext *glContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
    CIContext *ciContext = [CIContext contextWithEAGLContext:glContext
                                                     options:@{kCIContextWorkingColorSpace : [NSNull null]}];
    CGImageRef cgImage = [ciContext createCGImage:resultImage fromRect:[resultImage extent]];
    
    // 获取UIImage
    UIImage *filteredImage = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    
    return filteredImage;
}

代码讲解：

1. 将原图马赛克化，得到一张马赛克后的图片 ciOutputImagePixellate
2. 对原图人脸识别，并取识别后的人脸区域 maskImage
3. 使用 CIBlendWithAlphaMask 滤镜进行合成
4. 指定GPU 渲染

参考链接

Anonymous Faces Filter Recipe