2d lighting effect

I have a black texture (with 0.7f opacity) that I use as an overlay for darkness effect. I also have a small black circle sprite that I want to use as a mask to erase the darkness of the overlay. How do I achieve this? If this requires a custom shader, would you mind posting some snippets?

Below is sample image to illustrate what I want to achieve.

[37995-image+4.png|37995]

Lots of potential ways to achieve this. Try a Stencil Mask.