Do not darken part of the area in the darkened area. Canvas/Pixi. How?

Question

JavaScript

In general, I need to hate the entire background. I did it on pixi (it doesn't matter)
Now we need to leave the part of the zone that is in the darkened zone (background) not darkened.
How can i do this?
The picture below is what I need.

Answer 1

You can apply a semi-transparent mask
https://jsfiddle.net/Stalk/0gc4x7qw/ (click on the cat) The
mask itself can be prepared as a separate file or generated on the fly, on another canvas.