How to write an X11 app that follows the cursor

Question

I'd like to write a Linux screen magnifier that's customized to my liking. Ideally, the magnified window would be a square about 150 pixels wide that follows the mouse cursor wherever it goes.

Is it possible to do this in X11? Would it be easier to have an application window that follows the mouse around, or would it be better (or possible) to forget about the window altogether and just make the mouse pointer a 150x150 square that magnifies whatever's underneath?

Answer 1

This actually already exists, it's called Xmag (do a Google search for additional info). You might want to check out the source code for it if you want to know how it works.

EDIT: looks like I misread your question a little bit... if you want a magnified square to follow the mouse pointer around, I suppose it should be possible, but I don't know the technical details of how you'd do it. Regardless, the place to start is probably by looking at Xmag as a starting point.

Answer 2

Look at the source to xeyes?

Answer 3

I am unsure if this can run as its own app or would have to be integrated into your window manager. Either way, you would need libx11 (might have a different name from distro to distro). Also, I would suggest taking a look at swarp. I know this is not even close to what you are talking about, but the source code is only 35 lines and it shows what can be done with libx11.