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Re: Ntemacs chooses wrong font.

From: Kenichi Handa
Subject: Re: Ntemacs chooses wrong font.
Date: Wed, 11 Jun 2008 22:11:34 +0900
User-agent: SEMI/1.14.3 (Ushinoya) FLIM/1.14.2 (Yagi-Nishiguchi) APEL/10.2 Emacs/23.0.60 (i686-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO)

In article <address@hidden>, Jason Rumney <address@hidden> writes:

> Kenichi Handa wrote:
> > I currently explicitly generate a unibyte string for font
> > names just to avoid the font name encoding problem until the
> > font-backend codes gets stable.

> Does that mean that the encoding will eventually be done in generic 
> code, so I should avoid fixing this in w32font.c?

No.  The encoding and decoding must be done in each font
backend because only the backend knows how to do that.

> > Emacs at first checks if a charater is supported by the
> > frame font (here "Monaco-10") to avoid unnecessary looking
> > up of fontset table .  If supported, the frame font is used.
> > And, in your case, the font backend on Windows says that the
> > frame font supports it.  That is the problem.

> The problem appears to be that the system API used in one of the 
> encode_char functions on Windows (I don't know whether it is uniscribe 
> or gdi) seems to return a space glyph for unsupported characters in some 
> fonts, instead of 0 (which is ".notdef" according to the truetype spec).

It seems that this is a serious problem, but it's
unbelievable that Windows doesn't have a proper API to check
whether a font supports a specific character or not.

> Perhaps C-u C-x = should also report which font backend a font belongs 
> to, to make tracking these sorts of bugs down easier.

Ok, I'll add that soon.

> > It seems that you saved the file with some of legacy
> > encoding (e.g. euc-cn, big5).  On reading such a file, Emacs
> > adds a charset text-property (e.g. chinese-gb2312, big5),
> > and if a character has such a property, Emacs doesn't try
> > the frame font, but does a normal fontset looking up
> > (because `charset' information may change the priority of
> > fonts).  So, your fontset setting above takes effect.
> >   

> Ah, that explains a lot.

> > Perhaps, we should not try the frame font for a certain
> > group of charcters (e.g. han, indic, ??).
> >   

> Where is the has_char function used? On Windows, this should work to 
> filter out unsuitable fonts, as it checks the character against the 
> font's supported scripts.

The has_char method is called in fontset_find_font (in
fontset.c) to decide that the selected font is usable for
a specific character.

Kenichi Handa

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