title: How to make a hole in Unity UI?
body: <p>I want to make a reusable tutorial system for my games. My idea is to use a semi-transparent black panel to block every thing including clicks, but cut a hole on it (with a customized transform e.g. a button on other layers that you want to guide the player to click) to reveal what's behind the hole, and also users' clicks can go through the whole to interact with whatever behind the hole only.</p>
  
  <p>I've been searching for many hours on the internet but still can't find a solution. So what is the proper way to do it? Thank you!</p>