[XeTeX] XeTeX and diacritics

[Ross Moore]

Hi Arash,

On 25/03/2008, at 6:33 AM, Arash Zeini wrote:

> ----- Original Message ----
> From: Ross Moore <ross at ics.mq.edu.au>
> To: Unicode-based TeX for Mac OS X and other platforms <xetex at tug.org>
> Sent: Monday, 24 March, 2008 7:19:56 PM
> Subject: Re: [XeTeX] XeTeX and diacritics
>
> [...]
>
> Another question is:
>   Does it matter what is done at the input or macro levels?
>   Does XeTeX produce the same output in the PDF whether a precomposed
>   character or combining sequence is used, when there is a choice?
>
>
> If I understand you correctly, this is what I have been trying to  
> point out.

What I mean is that XeTeX, as in any TeX system, first "tokenizes"
the input characters.

So if the tokenized form of a  letter + composing character
is the same as the tokenized form of the pre-composed glyph,
then it doesn't matter what you do in the LaTeX source,
or within macros, since the result must be the same.

The above statement isn't quite true, since you can get the
letter and combining character tokenized independently,
then placed adjacent when being typeset.
But you can see the point of my question:
is there something to be done in macros, or can it only
be done by XeTeX itself?
e.g.,
  should XeTeX detect precomposed characters and output them
to .xdv  split into the letter + combining form?
If this isn't always desirable, can there be a switch
to control whether this is done or not?

Given that "desirability" here may depend upon exactly which
characters are available in the font, then should part of
this involve checking the font in detail before deciding
what form to output?

> For some diacritics it doesn't matter which input method you use or  
> better: the difference might be so small that it doesn't matter,  
> there is always a difference. But try two chracters side by side  
> with two different methods and you will see the difference. As I  
> mentioned earlier, an underlined z from Gentium differs  
> significantly from a \b{z}.
>
> Regards,
> Arash

Hope this helps,

	Ross

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Ross Moore                                       ross at maths.mq.edu.au
Mathematics Department                           office: E7A-419
Macquarie University                             tel: +61 (0)2 9850 8955
Sydney, Australia  2109                          fax: +61 (0)2 9850 8114
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