Re: [Paps-discuss] Combining characters not rendered properly

[<ar...@li...>]

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Jan Willem Stumpel wrote:
> Arne Götje (高盛華) wrote:
>> The fonts need to contain a) the base glyphs b) the combining 
>> accents c) "anchors" in the GPOS table to tell the rendering 
>> engine where exactly to place the accents. In fontforge this is
>> done easily. :)
> 
> I am sure I detect some irony here.. Anyway it is true that in all
> cases when a), b), c) are fulfilled (but there are not many of
> those), combining accents work (at least for *single* accents).
> And they work (more or less by luck) also in some other cases.
> 
> I suppose for the Unicode "*multiple* combining accents" mechanism
> to work, more complicated anchor classed ought to be defined
> (allowing, e.g., "accent on top of accent"). But it seems no
> actual font does this at the moment. In the case of the multiple
> accents of Classical Greek, Openoffice seems to do OK. But I think
> Openoffice uses another mechanism.
> 
> So the advice to users has to remain: use pre-combined accents
> whenever possible. Don't count on the "combining accents"
> mechanism to work. It won't, except from some lucky cases.

yes, it depends totally on the font to define the *position* of the
accents (and weather or not they can be stacked). But it depends on the
rendering engine to *interpret* the information the font gives about the
accents.

BTW: there was no irony in my statement. In Fontforge it is really easy
to define the "anchors". For all pre-composed Latin based combinations,
you can get it done with around 10 anchor classes, including the stacked
ones for Vietnamese.

The difficulty is to decide how the combinations should be displayed,
i.e. which "standard" to follow and which scripts to support.
You need to define the anchor points, both for the base glyphs and the
combining accents, separately and for each possible combination. This is
quite some work...

In my CJK-Unifont (http://www.cjkunifonts.info) project, I have used
"anchors" to display compositions, which are used in the Minnan language
(or better it's romanization) and which are not available as
pre-composed glyphs in Unicode.

Example: o <U+0301> <U+0358> -> ó͘

However, I made no attempts yet to implement this for the already
existing pre-composed glyphs, due to lack of time and low priority for
my project.

> 
> Thanks again for your explanation.

You are welcome. :)

Cheers
Arne
- --
Arne Götje (高盛華) <ar...@li...>
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