Add a key to "Hold" mouse in movement direction like a stick

[gsergeantGTHB]

Currently it's nearly impossible to watch those TV Broadcasts because the game expects you to use gamepad and keep your stick held in one angle to maintain frequency, a key to "lock" the mouse in whichever direction it is moving (like Left Alt) would solve this

[psxrestore]

I'll be sure to account for this as I work on the custom mouse look implementation. I'll likely prevent it from locking to the center of the screen.