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 12:23:04 +0200
>> 
>> 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.
>
> Why not simply include the frame pointer in the hash?  

With igc, frames move in memory, face caches are malloc'd.

> Adding a pointer to a number looks kludgey, and might even make the
> hash weaker.

If you have something better, please tell.