Re: Q: child frames on ttys

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

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

>> It was discussed in some length in a thread "Implementing child frames
>> on terminal" starting here
>>
>> https://lists.nongnu.org/archive/html/emacs-devel/2022-07/msg00301.html
>>
>> but IIRC nothing ever came out of it.
>>
>> martin
>
> Thanks for the pointer, Martin!

I've taken a look today, and I think the tty stuff is in principle still
like it was when I wrote it, plus some additions like multi-tty of
course.

Anyway, I think the below would be a viable plan how to add child frames
for ttys. Or a very rough first approach.

Any comments? Did I overlook something important?

* What we have

Child frames are created with the =parent-frame= frame parameter on
GUIs. This parameter can be changed at any time to create a hierarchy
of child fremes. It can be reset to make a frame a non-child frame.

A terminal's =tty_display_info= contains a =top_frame= member which is the
topmost frame in z-order, where z-order is a bit misleading because
all frames currently occupy the whole terminal screen. IOW making a
frame the topmost frame obsures all other frames.

Redisplay considers topmost frames only (more than one for multiple
terminals).

The function =frame-restack= can be used to change the z-order of
frames. It currently does not handle tty frames.

=frame-list= contains child frames.

* Terminology

A =root frame= is a frame with no parent frame. It always occupies the
whole terminal.

* Steps

1. Let frames have arbitrary ~(x, y, w, h)~ except for root frames,
   which have ~(0, 0, terminal-width, terminal-height)~. Change
   =frame-geometry=.

2. Give root frames a =child_frames= list which is in z-order, topmost
   last. Add a =tty-frame-restack= which acts on this list.

3. In =redisplay_internal=, act only on root frames. Generating desired
   glyphs generates glyphs for the root frame, then child frames in
   z-order, topmost last, i.e. in the order of =frame::child_frames=.

4. Making a frame visible means making all children frames visible.

5. Do not clear the terminal, unless switching to another root frame.

6. Update: Build frame matrices for all windows visible on a terminal.
   Copy visible parts of child fraem desired glyphs to root frame
   desired glyphs. Then write to the screen.

7. After writing to the screen, copy visble parts of root frame
   current glyphs to current glyphs of children.

8. Add something like =ns-frame-list-z-order= for ttys.

* Don't

1. Allocate child frame glyphs from a common pool. Reason is clipping.
   Don't want to change glyph generation in redisplay to take clipping
   into account. It's not worth the effort.