Re: Redisplay issue

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 04 Dec 2015 13:01:31 +0200
> Sun-Java-System-SMTP-Warning: Lines longer than SMTP allows found and
> 	truncated.
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: yuan.mei.list@gmail.com, emacs-devel@gnu.org
> 
> > Date: Fri, 04 Dec 2015 11:21:57 +0100
> > From: martin rudalics <rudalics@gmx.at>
> > CC: yuan.mei.list@gmail.com, emacs-devel@gnu.org
> > 
> >  >> So it's the Cairo font backend.  59 text lines plus one menu bar line
> >  >> give the 60 pixels difference.
> >  >
> >  > I don't understand how can it do that with the same size of the same
> >  > font.  Some bug in ftcrfont.c, perhaps?
> > 
> > Do what?
> 
> Compute a different frame-char-height for the same font and font size.

In case this is not clear: xterm.c computes FRAME_LINE_HEIGHT as
follows:

  get_font_ascent_descent (font, &font_ascent, &font_descent);
  FRAME_LINE_HEIGHT (f) = font_ascent + font_descent;

So the result comes from 2 values determined only by the frame's
default font.  These values are returned by the font back-end that
accesses the font, so only the font back-end could have affected them
for the same font.