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

[Rich Felker <dalias@xxxxxxxxxx>]

On Mon, Dec 11, 2006 at 10:08:23AM +0800, "Arne Götje (高盛華)" wrote:
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> Rich Felker wrote:
> > On Sun, Dec 10, 2006 at 04:11:26PM +0100, Jan Willem Stumpel wrote:
> >> 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.
> > 
> > Well there are two flip sides to this situation. On the one hand
> > you're right, but on the other hand if no one tries to use the
> > combining characters, applications and fonts will remain broken. :(
> > Since I need to use scripts where combining is essential, I'm somewhat
> > inclined to hilight the brokenness in apps (by using combining chars
> > in more situations) in hopes that the authors will fix them...
> 
> In this case, *you* need to *define* which combinations you need and
> *how* they should be displayed. If they exist already as pre-composed
> glyphs in Unicode, then it's no problem to implement them... but if not,
> it's up to you to do the definition first and then either to modify
> existing fonts by yourself (e.g. by using fontforge), or ask the
> upstream author of the fonts to do it for you.

The case I need is just for Tibetan, and all the existing fonts
(except the broken stuff in GNU Unifont, which I'm hoping to
eventually get replaced with glyphs that halfway-work with dumb
overstrike) have working GPOS/GSUB data.

The issue I was talking about was more application support than font
support. Even if a font does not have glyphs for the combining
characters, a good rendering engine should be able to use the
precomposed glyphs in cases where they're encoded in Unicode. However
many apps don't work even with the combining characters in the font.
On Windows, whether it works is often dependent on the order the
characters are stored; I'm told that Hebrew specifically does not work
when stored in the canonical order, at least with certain fonts, but
does work when the combining marks are reordered. Firefox doesn't
support combining correctly at all unless you patch it and compile it
yourself with pango (yeah right, good luck...) on *nix or on Windows.

> If the application of your choice then still cannot display the
> combinations correctly, prod the maintainers of that application to
> either use a rendering engine which can interpret the GPOS table of TTF
> fonts, or hack the support in by themselves, or (the best solution)
> forward the request to the upstream maintainer of the rendering engine
> they use...

*nod* these are all good suggestions.

Rich


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