[1.16.1] Getting mouse movements when mouse is focused

[DavidQF555]

I am trying to use mouse movements for a hud menu's selection process, but I ran into the problem that the mouse's movements are all set to 0 because the mouse isn't technically even on the screen. Is there a way to get the physical mouse's movement even when the mouse's pointer is not on the screen? The game has to parse physical mouse movements into camera movements somewhere right? So where could I get these physical movements? 

 

I've tried using head rotation to solve this, but I've actually given up with the trig required for it. 
 

Someone gave me some advice to use GLFW to get mouse movements, but I have no idea how to get the Callback that Mojang uses. I also looked at the GLFW_RAW_MOUSE variable in InputMappings, which looked very promising, but I have no idea how to use it. I was able to use the GLFW class to get cursor movements, but that doesn't work either because the cursor doesn't move. I need to get the direct mouse movements and not the cursor positions. 

Edited November 15, 2020 by DavidQF555
Added detail