[XeTeX] missing characters and msgs

[Mike Maxwell]

Jonathan Kew wrote:
> On Sat, Aug 22, 2009 at 4:27 PM, Mike Maxwell<maxwell at umiacs.umd.edu> wrote:
>> I'm getting a msg from xetex about missing characters in a font; I'm unclear
>> whether I should worry...
>>
>> The warning is:
>> -----------
>> Missing character: There is no X in font
>> [/groups/tools/fonts/NafeesNastaleeq
>> _v1_02.ttf]/ICU:script=arab,!
>> -----------
>> Some comments:
>> 1) The actual missing character is not X, but U+200C = ZWNJ.
> 
> I wonder if you are viewing the terminal output with a font where ZWNJ
> is not present, and the "missing glyph" looks like a (boxed?) X.

Sorry, I just used the 'X' as a placeholder in the email.  Nothing 
visible shows up in the logfile, although the character is there.

>> 2) At the end of the xelatex run, I get the msg
>>      LaTeX Font Info:    Some font shapes were not available,
>>      defaults substituted.
>>   I'm guessing this means that xelatex substituted a ZWNJ from
>>   some other font...
> 
> No, xetex does not do font substitution. So if your text contains
> ZWNJ, but this is not supported by the font you're using, you'll get
> that font's "missing glyph", which may be a box or blob of some kind,
> or may (if you're lucky, in this case) be an invisible glyph.

We seem to be lucky.

> If it happens that the font you're using renders missing glyphs as
> zero-width, invisible glyphs (rather than as some visible artifact),
> then in the case of ZWNJ you'll actually be getting the result you
> wanted -- but more by chance than anything else!

Apparently!  (at least that's what people who can read Nasta'liq tell 
me)  (BTW, the font is Nafees Nastaleeq, v1.02.)

> You could consider making ZWNJ an active character and defining it as
> a zero-width kern; for most purposes, this will give the effect of a
> ZWNJ without relying on the font to support it.

I was assuming xetex was substituting another font.  I might try that 
fix, although it's low on my priority list, since this seems to be 
working by luck...
-- 
    Mike Maxwell
    What good is a universe without somebody around to look at it?
    --Robert Dicke, Princeton physicist