In fact, I wasn't thinking about Input class at all.
We could have in Window class something like a friend method with our WindowImpl and when we ask for a new WindowImpl, we give as parameter a Window such that the WindowImpl could call the friend method to set the initial cursor pos.
However, it may look a little bit overkill compared to calling the GetCursorPos() function inside Input... At least all the OS-impl is in the same place. :roll: