Programmatically take a screenshot of specific area

Question

Like you can see in my code, I take a screenshot and save it to the photo album.

//for retina displays
if ([[UIScreen mainScreen] respondsToSelector:@selecto         


        

Answer 1

You need to make two changes in order to only grab a portion of the screen:

1. Create a smaller image - use the size of the rect you'd like to capture.
2. Move the origin of the context that you're rendering into to be negative x/y of the rect you'd like to capture.

After that, you just render the layer into the context as you were doing, and you should get what you're looking for. Something like this ought to do it:

CGRect grabRect = CGRectMake(40,40,300,200);

//for retina displays
if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
    UIGraphicsBeginImageContextWithOptions(grabRect.size, NO, [UIScreen mainScreen].scale);
} else {
    UIGraphicsBeginImageContext(grabRect.size);
}
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(ctx, -grabRect.origin.x, -grabRect.origin.y);
[self.view.layer renderInContext:ctx];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImageWriteToSavedPhotosAlbum(viewImage, nil, nil, nil);