There's really no need. That's a bunch of work for nothing.

I tested my remarks a minute ago. It is correct. You can make a .tga image 2048x2048 pixels that has only a tiny dot in the center, with the rest transparent. Nothing will happen while you're over the transparent parts, but when the mouse is over the little dot, you can click the button and activate the function you assigned. I can do the same thing with a dollar sign, a cross, a sombrero, or a leprechaun button. It doesn't matter. The mouse does NOT detect the transparent parts of a button. Please, just use .tga images with transparent parts... It's soooo easy...

NO need for a "circular image", NO need for window(s), NO need to "slice" up anything...