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Re: Converting compositions to strings
From: |
Eli Zaretskii |
Subject: |
Re: Converting compositions to strings |
Date: |
Mon, 30 Jan 2017 18:52:00 +0200 |
> Cc: address@hidden
> From: Clément Pit-Claudel <address@hidden>
> Date: Mon, 30 Jan 2017 11:39:09 -0500
>
> On 2017-01-30 10:18, Eli Zaretskii wrote:
> > The information about this can be found in the doc strong of
> > compose-region, under COMPONENTS.
>
> Thanks. This covers only "relative" compositions, right? Is there more
> information on non-relative compositions somewhere?
No, AFAIK this documents both relative and rule-based compositions.
> > The ones that seem to be relevant to what you are looking for (I'm
> > guessing) are a small class, and I don't think you can discern them
> > from the others unless you look at the "rules" parts of a
> > composition.
>
> Looking at the rules sounds fine; thanks! I think these compositions form a
> small class in terms of what Emacs supports, but that class seems to most if
> not all uses of composition that I see in my daily use of Emacs (where are
> other compositions used, beyond character spacing in what-cursor-position?).
>
> Based on your pointers, the following seems to work OK for me (I guess it
> could be extended to cover the (Bl . Br) case, but I haven't seen that pop up
> yet in practice).
>
> (defun esh--parse-composition (components)
> "Translate composition COMPONENTS into a string."
> (let ((chars (list (aref components 0)))
> (nrules (/ (length components) 2)))
> (dotimes (nrule nrules)
> (let* ((rule (aref components (+ 1 (* 2 nrule))))
> (char (aref components (+ 2 (* 2 nrule)))))
> (pcase rule
> (`(Br . Bl) (push char chars))
> (_ (error "Unsupported composition COMPONENTS")))))
> (concat chars)))
I think if we want to be able to produce text with all the text
properties and overlays expressed explicitly as text, we need to write
a back-end for xdisp.c that "displays" to a buffer. It shouldn't be
hard, the number of interface routines a back-end needs to support is
not large; see 'struct redisplay_interface' in dispextern.h.