Re: Pixel-based display functions

[Lars Ingebrigtsen <larsi@gnus.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Lars Ingebrigtsen <larsi@gnus.org>
>> Date: Fri, 30 Jan 2015 17:37:00 +1100
>> 
>> `font-get-glyphs' on a large region is quite fast, but since the font
>> may vary, I'm calling it on a char-by-char basis, and that's s-l-o-w.
>
> That's your problem: you should call it on a run of characters that
> have the same face.  Use next-single-char-property-change to find
> where such runs begin and end.

The face doesn't say what font is going to be used.  If I put 日本語
here, the entire preceding line has the same face, but two different
fonts.

I've done further experimentation, and it turns out my previous analysis
was kinda wrong.  `font-get-glyphs' isn't really the problem --
`font-at' is.  Calling it once per character is just way too slow.

If you have a handy function that can segment lines according to font
(even though it can't say what the font is (yet)), that would be useful.
If I could (on the first line there) just call `font-at' twice, I think
that would allow me to write an algorithm that should be fast enough.

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