Re: Pixel-based display functions

[Lars Ingebrigtsen]

Eli Zaretskii <address@hidden> writes:

> 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.)

If this can be done as fast as collecting the line data in C, that would
be fine.  But I would assume that there's quite a lot set-up overhead
before getting started.  For instance, calling `window-text-pixel-size'
ten times over separate lines instead of once on a region is way slower.

But if there's no setup overhead, then doing it per line basis would be
fine. 

>  . 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?

Yes, including all that stuff is necessary to do the line filling.

>    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?.)

Hm...  I hadn't though of that.  Well, in the shr case, there are no
overlays at all, and the only display strings are `align-to' one, I
think...

>  . 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?

Passing in an optional window, or if that's nil, the current window,
would be fine for shr's use case.  

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/