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Re: Pixel-based display functions

From: Lars Ingebrigtsen
Subject: Re: Pixel-based display functions
Date: Fri, 30 Jan 2015 18:27:23 +1100
User-agent: Gnus/5.130012 (Ma Gnus v0.12) Emacs/25.0.50 (gnu/linux)

Eli Zaretskii <address@hidden> writes:

>> From: Lars Ingebrigtsen <address@hidden>
>> 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

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/

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