Re: Q: child frames on ttys

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

martin rudalics <rudalics@gmx.at> writes:

>> So, this seems to work, at least in principle. Where in principle means
>> I didn't try much yet, but it looks like I can at least display
>> overlapping child frames.
>
> The screenshot looks good.  The question is how much resources it takes
> to turn the visibility of child frames on and off.  I conjecture that
> restoring the original frame glyph matrix could/should be even cheaper
> than handling the corresponding expose events on graphic frames.

Hard to tell if it's cheaper than on GUIs, but my gut feeling is that it
won't be too expensive. But it remains to be seen, I'm not yet that far.

> I wonder whether you should invariably show truncation/continuation
> columns on child frames and give them a same background as line numbers,
> title bars and modelines to make the child frame stand out more against
> the overlapped frame.  At least optionally.

Yeah, that's also still open. I'd like if background-color and
foreground-color frame params did something reasonable, at least on
child frames.

And I think I'd also like to have optional frame borders,
with border-width or something. Something lile +-| with display table
entries for the edges, sides, and horizontal lines.

>> I have a question regarding the child frame feature in general though.
>>
>> As I said before, I want to use them for Corfu and Posframe, the latter
>> with Vertico and Transient. But the child frame feature looks like
>> something much more general, more like a general MDI feature, as opposed
>> to SDI. And my question is: Is that actually used somewhere? In some
>> package, or in Emacs itself? If it is, I'd be grateful for a pointer.
>
> Initially, I wrote the child frame code because I found the necessary
> APIs for Windows and X and planned to use them for tooltips.  Later I
> found out that they are not really useful for that purpose because on
> graphic displays tooltips are often displayed outside the parent frame
> while child frames are clipped.  Moreover, tooltips usually disappear
> when the user interacts in some way and the major advantage of child
> frames - namely that they move together with their parent - gets lost in
> practice.  I even spent some time on 'window-largest-empty-rectangle' to
> avoid that tooltips hide any normal text.  Currently, I'm still using
> normal frames for tooltips while I'm using child frames mostly for
> displaying the minibuffer.

Hm, okay. Thanks for the insight.

> Child frames can be used to overcome the classic restriction that Emacs
> windows are "tiled".  'display-buffer-in-child-frame' conceptually
> provides that feature.  But I don't see why that would need any special
> treatment on TTYs.  Why do you think that MDI vs SDI would impact the
> design of child frames on TTYs?

It wouldn't impact the design, I think. What I'm thinking of is
basically if I can get by supporting only what I really need for Corfu
and Posframe (+ Vertico + Transient), and nothing more, without
implementing the whole thing.

>> (Background is of course that I'm trying to assess how much work is
>> ahead, and if I want to do it :-).
>
> I suppose that visibility and restacking of child frames and size
> changes of child frames and their ancestors are the corner issues.

That's one thing. Another big one is the silent assumptioin that on ttys
there exists only one visible frame and that frame occupies the whole
terminal. Hard to find and pops up again and again. 

> Once these have been resolved, the code should be pushed and you
> should wait for user feedback.

It is already pushed, but to a branch in my fork :-).

Anyway, this can take a bit.