Re: "Final" version of tty child frames

[Gerd Möllmann]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Gerd Möllmann <gerd.moellmann@gmail.com>
>> Cc: emacs-devel@gnu.org
>> Date: Tue, 22 Oct 2024 10:21:43 +0200
>> 
>> Thanks for taking a look.
>
> Can you explain this comment and the code change:
>
>   +         /* Struct frame can move with igc, and so on.  But we need
>   +            something that takes different frames into account. Use the
>   +            face_cache pointer for that which is malloc'd. */
>   +         if (glyph->frame && glyph->frame != f)
>   +           face_id += (ptrdiff_t) glyph->frame->face_cache;
>
> Why do we need to take the frame into account here?  Is this relevant
> to the current GC used on master?

I can try.

A combined frame matrix's glyph contents may come from different frames,
either the root frame one of its descendants (children, grandchildren
and so on). See copy_child_glyphs. glyph->frame is th eframe from where
the glyph stems. It is filled out when producing glyphs.

Face ids are valid only in frame's face cache. A Face with a given id in
one frame may be different from the same id another frame. So that's why
I'm taking the face cache into account here. Otherwise it could happen
that row hashes are the same although the contents are different. Not a
big deal, but one can avoid it, so I did.