UIImage offscreen rendering

UIImage+Offscreen.m

// Define callback blocks
// Success
__block typeof (self) weakSelf = self;
void (^successBlock)(NSURLRequest *, NSHTTPURLResponse *, UIImage *) =
        ^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {

            // Assigning an image that has not yet been decoded leads
            // to stuttering in UI animations
            // Forcing image decoding on a background thread fixes this
            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^(void) {

                // Force image decoding
                UIGraphicsBeginImageContext(image.size);
                [image drawAtPoint:CGPointZero];
                __block UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
                UIGraphicsEndImageContext();

                // Show image view on main thread
                dispatch_async(dispatch_get_main_queue(), ^{
                    [UIView setAnimationBeginsFromCurrentState:YES];
                    [UIView animateWithDuration:0.3 animations:^{
                        weakSelf.imageView.image = img;
                        weakSelf.imageView.alpha = 1.0f;
                    }];
                });
            });
        };