WINAPI Mouse movement diff via WinAPI

DirectInput still works fine for the time being, as there is still no complete replacement.

Raw Input might fit your bill: https://msdn.microsoft.com/en-us/library/windows/desktop/ms645536(v=vs.85).aspx

Yeah, sadly there isn't an alternative

Raw input does this

Yeah, Raw Input does but you still need to get the mouse initial position by WINAPI call GetCursorPos unless you now the direction but do not now the position of your cursor

GetRawInputData actually gives your the mouse motion in the X/Y directions, you can call it in response to a WM_INPUT event, after making sure to call RegisterRawInputDevice so that your window actually receives the events.

https://msdn.microsoft.com/query/dev15.query?appId=Dev15IDEF1&l=EN-US&k=k(WINUSER%2FGetRawInputData);k(GetRawInputData);k(SolutionItemsProject);k(DevLang-C%2B%2B);k(TargetOS-Windows)&rd=true

I second or third using RawInput. Since eventually DirectInput will no longer be supported. It's pretty easy to use too.