Re: Redisplay issue

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 2 Dec 2015 20:55:25 -0800
> From: Yuan MEI <yuan.mei.list@gmail.com>
> Cc: emacs-devel <emacs-devel@gnu.org>
> 
> > +  unblock_input ();
> >  }
> >
> 
> Unfortunately this did not solve the problem.

That was the only difference I could spot between 2 different code
paths into calling the display back-end drawing routines: one which
works (the "normal" redisplay), the other that doesn't (when a frame
is exposed).

I guess at this point we need a Cairo expert to look into this and
find out what prevents the correct redisplay.  My gut feeling is that
it's some buffering at work, and Emacs simply doesn't tell Cairo to
"flush" the buffered drawing commands.  But I couldn't find the code
which would be responsible for that in the "normal" redisplay case.

> And I noticed something: comparing with and without cairo, even though
> the number of lines of text and other geometric parameters are
> identical (no .Xdefaults or any changes in .emacs.d/, the window
> (frame) height for with and without cairo are different.  Something
> about font handling are different?

Everything is different with Cairo, including the fonts: the Cairo
build has its own font back-end (see ftcrfont.c).

How large is the difference?  Do you see changes in frame/window
dimensions that correlate to those differences in height?