If I wanted to use the Unity Input Manager to register a keyboard input I’d conventionally use GetButtonDown, however as part of a self imposed learning project I’m shunning much of Unity’s perfectly good input manager version in favour of writing my own (almost certainly inferior) custom one. As such I’m now using GetKeyDown instead and referencing ones from my own manager which stores each input as a KeyCode. When it comes to mouse button pressing this also works because mouse0 and mouse1 are both available as KeyCodes, but mouse movement isn’t. What kind of equivalent is there that could allow me to obtain raw mouse delta values without requiring the Unity Input Manager’s axis system?
There are numerous control devices supported in Unity’s Input class. Be sure to take a look at their documentation and see what options are available to you.
To address your question directly, mouse input is primarily detected using Input.GetMouseButton(int) (and its Up and Down variants), Input.mousePosition, and input.mouseScrollDelta for the mouse wheel.
Furthermore, to get the per-frame mouse position change (i.e. mouseDelta), you can try something like this:
mouseDelta = Input.mousePosition - lastFrameMousePosition;
lastFrameMousePosition = Input.mousePosition;