Subtract UIView from another UIView in Swift

Question

I'm sure this is a very simple thing to do, but I can't seem to wrap my head around the logic.

I have two UIViews. One black, semi-transparent and "full-screen" ("overlayView"), another one on top, smaller and resizeable ("cropView"). It's pretty much a crop-view setup, where I want to "dim" out the areas of an underlying image that are not being cropped.

My question is: How do I go about this? I'm sure my approach should be with CALayers and masks, but no matter what I try, I can't get behind the logic.

This is what I have right now:

This is what I would want it to look like:

How do I achieve this result in Swift?

Answer 1

There might be another drawing solution but basically you have 4 areas that need to be handled. Take the square area above and below the space with full width and add the right and left side between them with constraints to eachother.