----- Message d'origine -----
De : "J.Pietschmann" <[EMAIL PROTECTED]>
Envoyé : 9 oct. 2002 15:30
Objet : Re: Fw: Arabic characters and FOP

> patrick andries wrote:
>  > (*) Does anaybody know how glyphs variants and ligatures (see the
>  > substitution feature in Opentype) should be selected from fo ? I
>  > there is currently no such mechanism. Should we wait until another
version of
>  > XSL-FO? Extensions ?
> IIRC the spec mentions it's at the whim of the processor to
> provide ligatures.
> There are also various code points assigned
> to ligatures and presentation forms, for example U+FB01, which
> could be used in the FO source (at the risk of confusing
> hyphenation, spell checkers and others).

Not a good idea, these code points are deprecated. Ligatures are glyphs not
characters, Unicode is about characters (yes, I know there are "historical"
and compatibility exceptions)

> If such characters
> are mapped to glyphs by a font, FOP can handle them.

The idea with OpenType (the merging of PS1 and TTF fonts) is to do allow to
render these ligatures at rendering time (as is necessary with many
non-latin based scripts), i.e. within the glyph space.

Also, some ligatures are purely discretionary (like the ligated fi you
mentioned in U+FB01). This behaviour should be driven by some styling
information, I would assume ("I want a nice ffl ligature here if present in
the font,  and here a ct ligature if present). I do not know of any
available means to specify this. The same is true for glyph variants (I
would like this particular ampersand variant). What are the CSS people doing
about this ? Should we follow them ?

> Also, the discussion whether presentation forms have to be
> expressed by the characters itself or out of band, for example
> as fonts, has never ended.

Unicode is quite plain about this, I believe  it even states somewhere that
the Arabic presentations forms were a bad idea . This is at least what the
technical director of the Unicode consortium said in an interview I
conducted (in French though :
« Ceci s'est déjà produit : ainsi aucune mise en ouvre Unicode de l'arabe ne
se préoccupe du grand nombre de ligatures arabes codées dans Unicode,
ligatures dont l'inclusion a constitué une erreur. Les implantations arabes
correctes utilisent les caractères arabes de base et étendus et délèguent la
formation des ligatures aux polices, comme il se doit.»)

P. Andries

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