Re: Make scroll-{up, down} move point to {start, end} of newly visible text

[Spencer Baugh <sbaugh@janestreet.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Spencer Baugh <sbaugh@janestreet.com>
>> Date: Mon, 31 Jul 2023 16:18:15 -0400
>> 
>> 
>> After I use scroll-up or scroll-down, I want to start reading the new
>> text on the screen.  But it's easy to lose track of where the new text
>> start, especially with larger values of next-screen-context-lines.
>> 
>> So, I would like scrolling to move point to the division between old and
>> new text.  Then the location of the cursor will help me keep track of
>> which text is new and which text is old.
>
> I don't understand, because what you want happens here by default:
> scrolling always puts at the top of the window the first line of those
> which constitute next-screen-context-lines.  So, for example, if you
> have next-screen-context-lines set to 5, C-v will put the 5th line
> from the window's bottom at the top screen line.

Ah, that's not quite what I mean...

> If by "new text start" you mean the first line that was not visible in
> the window before C-v, then set scroll-margin to the value of
> next-screen-context-lines, and then Emacs will put point at that first
> new line.
>
> Is that what you want?

Yes, that's exactly what I mean and want!  Perfect, and very clever!
That indeed moves point to the division between old and new text!

Ah, but there's a missing feature... I'd like it to also work as I
described when I use scrolling with a prefix argument.  That is, it
should move point to the division between old and new text even then.

So M-5 C-v would move point to 5 lines from the end of the buffer.
scroll-margin might interfere, but I still would want point to be at the
division between old and new text.