Re: Pixel-based display functions

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 06 Feb 2015 17:42:40 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: rudalics@gmx.at, monnier@IRO.UMontreal.CA, emacs-devel@gnu.org
> 
> > I think the ideal interface for this would be a function that returns
> > a vector of glyph widths in the region, possibly with one vector per
> > line.
> 
> I'll see what I can do.

A few preliminary questions about this:

 . Is it good enough to handle only a single physical line, starting
   from a given POSITION argument and ending at the first newline that
   follows POSITION?  (Handling of additional lines will then have to
   be done in Lisp.)

 . What to assume/do with the various display features, like overlay
   and display strings, images, align-to space specs, line-prefix,
   etc., that can be pertinent to the portion of text being processed?
   The easiest alternative is to handle them "as usual" in redisplay,
   i.e. the corresponding glyphs will be produced and included in the
   return value.  Is that OK?  If not, what else is needed for these
   use cases?  (Note that if a display or overlay string includes
   newlines, this means the result could span multiple screen lines --
   will that be a problem?.)

 . How will the caller specify the information about the display
   defaults, like the faces?  The usual way is that some window is
   specified, either explicitly as an argument or implicitly as the
   currently selected window, and all the defaults are taken from that
   window and its frame.  Is that good enough for your purposes?