Question

Is there a way to black out a region (defined by a frame) of a UIImageView without creating an overlaying UIView instance (with this frame) and blacking that out?

Is there similarly a way to reveal part of a UIImageView without using UIView instances to black out the rest of the image?

Answer 1

I am going to cheat a bit here and suggest that you use layer as they are light weight.

CALayer *blackLayer = [CALayer layer];
blackLayer.backgroundColor = [UIColor blackColor];
blackLayer.frame = imageView.bounds;
[imageView.layer addSublayer:blackLayer];

For the second part you can consider using a grid of layers (black). When user touches the image view, you can pick the layers from the area he has touched and remove them from the super layer i.e. the image view’s root layer.