Getting a screenshot of a UIScrollView, including offscreen parts

Question

I have a UIScrollView decendent that implements a takeScreenshot method that looks like this:

-(void)takeScreenshot {  
  CGRect contextRect  =          


        

Answer 1

Here's another way of doing it, which takes the zoom level into account. I have a scrollview with 4 different UIImageView layers in it, and I want to take a screenshot of their current state:

float theScale = 1.0f / theScrollView.zoomScale;
// The viewing rectangle in absolute coordinates
CGRect visibleArea = CGRectMake((int)(theScrollView.contentOffset.x * theScale), (int)(theScrollView.contentOffset.y * theScale),
                                (int)(theScrollView.bounds.size.width * theScale), (int)(theScrollView.bounds.size.height * theScale));

NSArray *layers = [NSArray arrayWithObjects:imageLayer1, imageLayer2, imageLayer3, imageLayer4, nil];
UIGraphicsBeginImageContext(visibleArea.size);
for (UIImageView *layer in layers) {
    CALayer *coreLayer = layer.layer;
    coreLayer.bounds = CGRectMake(layer.frame.origin.x - visibleArea.origin.x, layer.frame.origin.y - visibleArea.origin.y, layer.frame.size.width, layer.frame.size.height);
    [coreLayer renderInContext:UIGraphicsGetCurrentContext()];
}
UIImage *screenshot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

This takes the screenshot in absolute coordinates. That is, if you have a 2048*2048 image in the scrollview and you can see about a quarter of it, then regardless of the resolution of your screen it would take a screenshot of 512*512. If you want to take a screenshot at your screen resolution (say, 320*480) then you have to adjust the image as follows, directly after the above code:

UIGraphicsBeginImageContext(theScrollView.frame.size);
[screenshot drawInRect:CGRectMake(0, 0, theScrollView.frame.size.width, theScrollView.frame.size.height)];
UIImage *smallScreenshot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();