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Re: Pango-like font fallback (was Re: Russian numero sign)

From: Paul Pogonyshev
Subject: Re: Pango-like font fallback (was Re: Russian numero sign)
Date: Tue, 7 Mar 2006 22:39:29 +0200
User-agent: KMail/1.7.2

Kenichi Handa wrote:
> In article <address@hidden>, Paul Pogonyshev <address@hidden> writes:
> >> unify-8859-on-encoding-mode is not relevant how to read (or
> >> decode) Cyrillic characters encoded in UTF-8, nor how to
> >> display Cyrillic characters decoded into
> >> mule-unicode-0100-24ff charset.
> >> 
> >> Do you really mean that you solved the display problem by
> >> turning it off?
> > No, there is a misundestanding.  I meant `unify-8859-on-decoding'.
> So, you turned off unify-8859-on-decoding to solve the
> display problem, right?

Yes.  When it is off, newly typed Cyrillic characters are displayed OK.
When it is on, newly typed characters are displayed as boxes, even if
the buffer visiting an UTF-8 file already contains properly displayed
Cyrillic characters.

> Then I think the reason why you can't see Cyrillic
> characters while unify-8859-on-decoding is on is that your
> -adobe-courier-*-iso10646-1 font doesn't contain Cyrillic
> glyphs.

Yeah, I suspected that all the way :)  However, Emacs can do nothing
about the fact that the fonts out there don't provide support for all
the Unicode characters (and most fonts actually provide support for
only a tiny fraction of characters...)  Emacs could, however, use
multiple fonts to alleviate the problem, that's what I'm proposing
(for a future version.)

> > In general, Emacs shows most basic characters OK with unify-on-encoding
> > turned on and unify-on-decoding off, it's not like I need fancy
> > characters regularly.  However, Pango sure does a nicer job and I hope
> > your changes doing similar things get merged into the Emacs trunk.  That
> > is, if another stable version is ever released.
> Please note that Pango and the other modern rendering
> engines use TrueType font with a help of freetype/Xft and
> fontconfig libraries.  Emacs (and emacs-unicode-2 too)
> currently doesn't use them, but there exists an ongoing
> project for supporting TTF in Emacs.

That is a valid reason why Emacs cannot use Pango (yet), but it
doesn't mean Emacs cannot implement similar substitution heuristic
without Pango and for a different font class.  As I understand, you
did that in the `emacs-unicode-2' branch.  It is not something simple,
but Emacs is not simple to begin with.

> >> Please try to select "fontset->standard" by shift-mouse1.
> >> It makes "fixed" the default family, thus has the higher
> >> possibility of selecting an iso10646-1 font that support
> >> Cyrillic.
> > This doesn't seem to have any effect.  The screen flickers
> > but displays exactly the same fonts, no matter what I
> > choose in the menus. Probably because I have customized
> > faces, not sure.
> First of all, do you have any iso10646-1 X core fonts that
> support Cyrillic characters?

No idea, sorry.  How do I check?  As I wrote above, Emacs does
display Cyrillic characters (newly typed) when `unify-8859-on-decoding'
is off.  And already existing characters are displayed no matter if
that mode is active or not.


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