bug#25824: 25.1; bugs about display specfications

[Eli Zaretskii]

> Date: Fri, 24 Feb 2017 10:23:13 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 25824@debbugs.gnu.org
> 
> > From: ynyaaa@gmail.com
> > Cc: 25824@debbugs.gnu.org
> > Date: Fri, 24 Feb 2017 15:01:19 +0900
> > 
> > Eli Zaretskii <eliz@gnu.org> writes:
> > > Only if the replacement comes from a before- or after-string (in which
> > > case the text won't be replaced, so you will have to hide it with some
> > > invisible property).  Put the 'raise' display property on the overlay
> > > string, and you will have what you want.
> > 
> > Overlays are not editable with kill and yank,
> > so text properties are better.
> 
> Then I'm afraid you are out of luck, because Emacs doesn't support
> recursive 'display' properties, i.e. a 'display' property that is a
> string which has another 'display' property for (a part of) that
> string.
> 
> > > What the display engine does is reserve space above
> > > the baseline that is large enough for the enlarged font, and then draw
> > > the "X" with a negative offset relative to the baseline, by enlarging
> > > the 'descent' value of that particular glyph, which adds vertical
> > > space _below_ the line.
> > 
> > I wonder why the display engine does not take 'rase' into account
> > when reserving space above the baseline.
> 
> AFAIU, it's just a side effect of the implementation: 'raise' is
> implemented as modifications of the ascent or descent, so it behaves
> like these attributes of any glyph would.
> 
> > > Does the below do what you want?  If not, perhaps I don't understand
> > > what you mean by "centered".
> > >
> > >   (insert "A" (propertize "X" 'display '((raise -0.2) (height 2))))
> > 
> > It is enough for only one line.
> > With blank areas, emacs can display fewer lines.
> 
> Yes, there are limitations of what can be done in Emacs as far as text
> layout is concerned.

I've now clarified the relations between 'raise' and 'height' in the
ELisp manual, and I'm closing this bug.

Thanks.