I found a smudge tool example here Smudge Tool Tutorial

the problem is that the source code example is gone, and what you can download from the wayback machine crashes Xcode. So there’s no way to really get in to it and test it.
I used chatgpt to convert the objective-c example code to swift and I created a dummy project to try to make this work but it’s above my head and I can’t get it to work.
Because of the nature of the code it isn’t really possible to reduce it to something I can easily cut and paste here but I have uploaded the dummy project here : Test Project

The smudge tool I’ve created her only draws a single dot on the screen but does not smudge beyond that

I’ve tried getting chat gpt. to fix the code but it can’t