ios - CGContext 错误仅在模拟器中？

Question

在测试我的应用程序是否存在任何错误时，我注意到在模拟器中，当我调用其中一个函数将图像设置为 UIImageView 时，会抛出一堆 CGContext 错误，并且图像永远不会被设置。然而，在我的设备上(我在 iPhone 5、iPhone 3GS 和 iPad 3 上进行了测试)，这些 CGContext 错误都没有出现，并且图像设置得很好。

无论如何，我寻找了任何可以实现这一点的 CGContext 代码，以下是涉及 CGContext 的唯一方法:

- (void)setCropRect:(CGRect)cropRect
{
    if(!CGRectEqualToRect(_cropRect,cropRect)){
        _cropRect = cropRect;
        UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, 0.f);
        CGContextRef context = UIGraphicsGetCurrentContext();
        [[UIColor blackColor] setFill];
        UIRectFill(self.bounds);
        CGContextSetStrokeColorWithColor(context, [[UIColor whiteColor] colorWithAlphaComponent:0.5].CGColor);
        CGContextStrokeRect(context, _cropRect);
        [[UIColor clearColor] setFill];
        UIRectFill(CGRectInset(_cropRect, 1, 1));
        self.imageView.image = UIGraphicsGetImageFromCurrentImageContext();

        UIGraphicsEndImageContext();
    }
}

- (CGImageRef)newScaledImage:(CGImageRef)source withOrientation:(UIImageOrientation)orientation toSize:(CGSize)size withQuality:(CGInterpolationQuality)quality
{
    CGSize srcSize = size;
    CGFloat rotation = 0.0;

    switch(orientation)
    {
        case UIImageOrientationUp: {
            rotation = 0;
        } break;
        case UIImageOrientationDown: {
            rotation = M_PI;
        } break;
        case UIImageOrientationLeft:{
            rotation = M_PI_2;
            srcSize = CGSizeMake(size.height, size.width);
        } break;
        case UIImageOrientationRight: {
            rotation = -M_PI_2;
            srcSize = CGSizeMake(size.height, size.width);
        } break;
        default:
            break;
    }

    CGContextRef context = CGBitmapContextCreate(NULL,
                                                 size.width,
                                                 size.height,
                                                 8, //CGImageGetBitsPerComponent(source),
                                                 0,
                                                 CGImageGetColorSpace(source),
                                                 kCGImageAlphaNoneSkipFirst//CGImageGetBitmapInfo(source)
                                                 );

    CGContextSetInterpolationQuality(context, quality);
    CGContextTranslateCTM(context,  size.width/2,  size.height/2);
    CGContextRotateCTM(context,rotation);

    CGContextDrawImage(context, CGRectMake(-srcSize.width/2 ,
                                           -srcSize.height/2,
                                           srcSize.width,
                                           srcSize.height),
                       source);

    CGImageRef resultRef = CGBitmapContextCreateImage(context);
    CGContextRelease(context);

    return resultRef;
}

- (CGImageRef)newTransformedImage:(CGAffineTransform)transform
                      sourceImage:(CGImageRef)sourceImage
                       sourceSize:(CGSize)sourceSize
                sourceOrientation:(UIImageOrientation)sourceOrientation
                      outputWidth:(CGFloat)outputWidth
                         cropSize:(CGSize)cropSize
                    imageViewSize:(CGSize)imageViewSize
{
    CGImageRef source = [self newScaledImage:sourceImage
                             withOrientation:sourceOrientation
                                      toSize:sourceSize
                                 withQuality:kCGInterpolationNone];

    CGFloat aspect = cropSize.height/cropSize.width;
    CGSize outputSize = CGSizeMake(outputWidth, outputWidth*aspect);

    CGContextRef context = CGBitmapContextCreate(NULL,
                                                 outputSize.width,
                                                 outputSize.height,
                                                 CGImageGetBitsPerComponent(source),
                                                 0,
                                                 CGImageGetColorSpace(source),
                                                 CGImageGetBitmapInfo(source));
    CGContextSetFillColorWithColor(context,  [[UIColor clearColor] CGColor]);
    CGContextFillRect(context, CGRectMake(0, 0, outputSize.width, outputSize.height));

    CGAffineTransform uiCoords = CGAffineTransformMakeScale(outputSize.width/cropSize.width,
                                                            outputSize.height/cropSize.height);
    uiCoords = CGAffineTransformTranslate(uiCoords, cropSize.width/2.0, cropSize.height/2.0);
    uiCoords = CGAffineTransformScale(uiCoords, 1.0, -1.0);
    CGContextConcatCTM(context, uiCoords);

    CGContextConcatCTM(context, transform);
    CGContextScaleCTM(context, 1.0, -1.0);

    CGContextDrawImage(context, CGRectMake(-imageViewSize.width/2.0,
                                           -imageViewSize.height/2.0,
                                           imageViewSize.width,
                                           imageViewSize.height)
                       ,source);

    CGImageRef resultRef = CGBitmapContextCreateImage(context);
    CGContextRelease(context);
    CGImageRelease(source);
    return resultRef;
}

这些是 CGContext 错误:

Jul 31 23:37:37 app[10190] <Error>: CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 16 bits/pixel; 1-component color space; kCGImageAlphaNoneSkipFirst; 1504 bytes/row.
Jul 31 23:37:37 app[10190] <Error>: CGContextSetInterpolationQuality: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGContextTranslateCTM: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGContextRotateCTM: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGContextDrawImage: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGBitmapContextCreateImage: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGBitmapContextCreate: unsupported parameter combination: 0 integer bits/component; 0 bits/pixel; 0-component color space; kCGImageAlphaNone; 0 bytes/row.
Jul 31 23:37:37 app[10190] <Error>: CGContextSetFillColorWithColor: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGContextFillRects: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGContextConcatCTM: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGContextConcatCTM: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGContextScaleCTM: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGContextDrawImage: invalid context 0x0
Jul 31 23:37:37 app[10190] <Error>: CGBitmapContextCreateImage: invalid context 0x0

这些是我的应用程序中唯一使用 CGContexts 的方法。但就像我说的，这只发生在模拟器中，而不是在我测试过的设备上。

无论如何，这有什么特殊原因吗？或者有什么方法可以解决这个问题吗？

谢谢大家!

CGContextRef context = CGBitmapContextCreate(NULL,
                                                 size.width,
                                                 size.height,
                                                 CGImageGetBitsPerComponent(source), //8,
                                                 0,
                                                 CGImageGetColorSpace(source),
                                                 CGImageGetBitmapInfo //kCGImageAlphaNoneSkipFirst(source)
                                                 );

Answer 1

最有可能的是，您第一次调用 CGBitmapContextCreate失败了，因为你要求它做一些它不能做的事情。您可以在第一条错误消息中看到:

CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 16 bits/pixel; 1-component color space; kCGImageAlphaNoneSkipFirst; 1504 bytes/row.

CGBitmapContextCreate返回 NULL，其余的失败从那里级联。 (您不能在 NULL 上下文上进行操作，并且在 NULL 上下文上调用 CGBitmapContextGetImage() 会为您提供一个 NULL 图像，同样您也无法对其执行任何有用的操作。)

CGBitmapContextCreate 的文档状态:

For the list of supported pixel formats, see “Supported Pixel Formats” in the “Graphics Contexts” chapter of Quartz 2D Programming Guide.

这是direct link到该列表。