Re: How can I force updating mini window's header line when mode line is updated?

[Amos Bird <amosbird@gmail.com>]

Thanks for the kind help. I've made some progress and I'll report 
it on emacs-devel :)

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Amos Bird <amosbird@gmail.com>
>> Date: Wed, 25 Apr 2018 20:41:09 +0800
>>
>> Dear community,
>>
>> I'm trying to setup one mode line per frame. Here is what I've
>> done.
>>
>> 1. turn on the head line of mini window by tweaking
>> window_wants_header_line.
>> 2. change shrink_mini_window so that it shrinks mini window to 
>> two
>> lines instead of one.
>> 3. (setq-default header-line-format mode-line-format)
>
> It's great to hear someone hacks the display code to add 
> features.
> However, these issues are best discussed on emacs-devel, not 
> here.
> Who knows, we could even ask you to contribute the code ;-)
>
>> However the header line doesn't get updated at all. It seems
>> xdisp.c only provides ways to update mode line, and I've 
>> reached
>> the limit of my emacs-fu. How can I achieve this without 
>> hacking
>> tons of the display logic? Many thanks!
>
> I think you need to modify window_wants_header_line, it 
> currently has
> hard-wired knowledge that a minibuffer window will never display 
> a
> header line.
>
> Once that is done, the feature should work, because the same 
> triggers
> that update the mode line also update the header line, so this:
>
>> It seems xdisp.c only provides ways to update mode line
>
> is inaccurate.  See the part of redisplay_window immediately 
> following
> the 'done' label: it calls display_mode_lines, which displays 
> both the
> mode line and the header line.


--
Amos Bird
amosbird@gmail.com