Re: Request for pointers and advice: displaying several buffers inside a single window

[Eli Zaretskii]

> From: Dmitrii Korobeinikov <address@hidden>
> Date: Sat, 11 Apr 2020 01:09:08 +0600
> Cc: Yuan Fu <address@hidden>, address@hidden, Eli Zaretskii <address@hidden>, 
>       emacs-devel <address@hidden>
> 
> >From what I saw, there's not a unified core interface on top of that c
> array. So, would need to modify each place that makes a use of it.
> (for a couple of examples, see text_outside_line_unchanged_p in
> xdisp.c, looking_at_1 in search.c)

I'm not sure why you came to that conclusion.  Emacs's internals
access buffer text directly when needed, for speed.  Interfaces like
BEG_UNCHANGED/END_UNCHANGED, BYTE_POS_ADDR, GPT, and others are no
less "core interfaces" for accessing buffer text than functions in
insdel.c.  I would even consider insdel.c as a layer _above_ the
low-level interfaces such as BYTE_POS_ADDR.

And looking_at_1 does what it does because it needs to pass buffer
text as 2 C 'char' arrays to regex routines, so I don't think it's any
evidence to anything.  It's just a trick to pass non-contiguous text
to a function that needs contiguous text.

> The good news is: I believe xdisp.c wouldn't have to be modified all
> that much if the regions are enforced to start on different lines.

How so?  The display code accesses the buffer text directly, using
BYTE_POS_ADDR.