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Re: Is there something like `on-display-functions'?

From: Alan Mackenzie
Subject: Re: Is there something like `on-display-functions'?
Date: Thu, 28 Jan 2010 14:47:07 +0000
User-agent: Mutt/1.5.9i

Hi, Eli,

On Thu, Jan 28, 2010 at 07:54:34AM -0500, Eli Zaretskii wrote:
> > Date: Thu, 28 Jan 2010 10:38:56 +0000
> > Cc: Stefan Monnier <address@hidden>, address@hidden
> > From: Alan Mackenzie <address@hidden>

> > As a zero order approximation, something like
> > `before-display-functions', where an element would look like this:

> >    (defun foo-before-display (buffer beg end) .....)

> > , BEG and END defining the piece of BUFFER about to be displayed.
> > The hook would be called before fontification.

> What do you mean by ``before fontification'', and why does it have to
> be before that?

I don't really know what I mean by "before fontification".  I want it so
that if in `foo-before-display' I put syntax-table TP on < and >, and
point happens to be at one of them, show-paren-mode will work to
highlight them.

> > (Is it possible in general to determine BEG and END before
> > fontification?).

> Only approximately.  E.g., imagine a `display' property whose value is
> a long string -- without computing how it will be displayed, there's
> no way of knowing how much of the screen estate it will take.  As
> another, less exotic example, imagine font-lock definitions that
> enlarge the font significantly: until you fontify that part, you
> cannot know how much screen space it will take.

> BEG and END are well known _after_ redisplay prepares what will be
> shown on the glass, though.  Therefore, please tell why do you ask to
> call this hook _before_ fontifications.

See above.

Maybe an alternative to a hook here would be to allow an application to
specify that some text property (say, 'c-templatified) is to be
"special", and when the displayer detects the TP has changed, it calls an
associated function.  'c-templatified would be analogous to 'fontified.

Alan Mackenzie (Nuremberg, Germany).

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