Hey, I come with a question.

These icons:

fascinate me. I'd like to know how these icons were made. It's probably something so simple it's stupid, but I can't figure out how to make half the icon disappear without white showing up in the back, thus making it look like a completely square icon.

So. How does one erase half the icon to get an image like that?


edit: I use Photoshop CS.