Open Radar

 
Summary:
We are seeing occasional crashing (many hundred per day), plus many more "nil" return values for UIGraphicsGetImageFromCurrentImageContext (many thousand per day) when scaling images.

Steps to Reproduce:
We cannot reproduce this crash (nor the nil return value), but with 100 million users view billions of images, it happens enough to want to get to the bottom of it.

Code:
UIImage *TIPImageScaled(UIImage *sourceImage, CGSize targetDimensionsOrZero, UIViewContentMode targetContentMode)
{
    if (!sourceImage) {
        return nil;
    }

   UIImage *image = sourceImage;

    CGSize dimensions = TIPImageGetDimensionsWithoutScale(image);
    targetDimensionsOrZero = TIPImageScaleDimensions(dimensions, targetDimensionsOrZero, targetContentMode);

    // If we have a target size and the target size is not the same as our source image's size, draw the resized image
    if (!CGSizeEqualToSize(CGSizeZero, targetDimensionsOrZero) && !CGSizeEqualToSize(dimensions, targetDimensionsOrZero)) {
        CGFloat scale = [UIScreen mainScreen].scale;
        CGSize targetSize = targetDimensionsOrZero;
        targetSize.width /= scale;
        targetSize.height /= scale;
        CGRect drawRect = CGRectMake(0, 0, targetSize.width, targetSize.height);
        BOOL hasAlpha = TIPImageHasAlpha(image, NO);

        UIGraphicsBeginImageContextWithOptions(targetSize, !hasAlpha, scale);
        if (!image.images.count) {
            [image drawInRect:drawRect]; // <--- can crash here
            image = UIGraphicsGetImageFromCurrentImageContext(); // <-- can return nil (I might have seen it crash too)
        } else {
            NSMutableArray *newFrames = [[NSMutableArray alloc] initWithCapacity:image.images.count];
            for (UIImage *frame in image.images) {
                [frame drawInRect:drawRect];
                UIImage *newFrame = UIGraphicsGetImageFromCurrentImageContext();
                [newFrames addObject:newFrame];
            }
            image = [UIImage animatedImageWithImages:newFrames duration:image.duration];
         }
         UIGraphicsEndImageContext();
    }

    if (image == sourceImage) {
        TIPImageDecode(image);
    }

    TIPAssert(image != nil); // <-- assert can trigger

    return image;
}