Re: Temporarily select-window, without updating mode-line face and cursor fill?

[Eli Zaretskii]

> From: JD Smith <jdtsmith@gmail.com>
> Date: Sat, 1 May 2021 14:46:31 -0400
> 
> I’m working on a small “in mode-line” scroll bar, and have implemented mouse 
> events for it, which are working well.  When I interact using the mouse with 
> the mode line of a non-selected window, I need to have that window 
> temporarily selected, so I can calculate its line offsets and move within it. 
>  But (just as for regular scrollbars), I’d like to retain the originally 
> active window afterwards.

Please explain in more detail why do you think you need to select the
window.  What are those "line offsets", and why "move within it"
requires to select the window?