I figured that the window class could keep two functions for transforming between the screen and the current view setting.
In the case that you set up a view that's not aligned to the pixels of the screen, the window could have a ScreenToView and ViewToScreen transform function so you could easily get the mouse position in the active view.
It's fairly straightforward to do it yourself, but it's easy to get wrong a few times before it's right. Another of those convenience things, but I think it'd make sense with the Window - View feature that's already in.