Y-axis inversion is an alternate to whatever are generally defined as the standard camera controls for a game. Standard camera controls normally have the 'looking up' control mapped to a mouse or controller being pushed forward. Y-axis inversion has the opposite action, where mouse or controller being pushed forward results in the camera being pointed down. This is also the standard control scheme for most flight simulators with joystick controls, and many PC gamers transferred this control scheme over to other games which involve any type of camera control (including first and third person three dimensional games). Therefore, the vast majority of games have an option to toggle from standard to inverted camera control.
Generally speaking, the PC gaming community will modify popular games if they lack a y-axis inversion option. However, some games are not mod-able in this fashion, and requires more brute force methods of enabling y-axis inversion on a system-wide level.
Polynomial's Mouse Inverter is currently the best option for forcing inverted mouse controls on PC.
SakasaMouse is a freeware program was developed as a 'joke' program to install on the victim's computer, which would invert all mouse movement on y-axis as well as x-axis. However it is one of the few freely available programs which can invert the y-axis globally on modern versions of Windows.
Version 1.03 was last updated on 29 October 2006, and has been tested to work on Windows XP, Vista and 7 and also in its x64 variant. It is available to download on ARA's website (a Japanese website).
This driver is a utility developed by MAF-Soft, which works by installing a driver over a specific mouse. Its x64 variant is in beta, and does not support USB mice, and the x86 version will not work on x64 Windows. The personal license costs €12.
Once the driver is installed, y-axis inversion can be activated using these steps:
A version without the use of a middle mouse button is available by contacting the author of the driver.
Some work has been done to develop y-axis inversion as an AutoHotkey script. However, this has some issues when used in DirectInput games.
I tried many options above to get my y-axis to invert only when middle mouse button was clicked. I tried all the above and failed. I finally got this to work on Battlefleet Gothic: Armada! Turns out what I had to do was use a combination of the two. Credit goes to this guy (sorry I don't know how to put a reference in but I'm so excited I had to share). Just change RButton to MButton in the autohotkey script. So simple.
Xpadder can be used to invert the y-axis of the right analogue stick by setting the 'Stick 2' vertical movement to 'Inverted Axis RY'. It may be necessary to override the game's native controller support for this to work.
Durazno is a XInput wrapper that simply sits between the controller and the game so as to allow for input customization.