bug#3174: NS font selection still broken

[Adrian Robert]

> I've been looking at the trace from nsfont and, more importantly, ` 
> (reverse font-log)' from font.c.
>
> To display [“] 201C  LEFT DOUBLE QUOTATION MARK, we get the log  
> below (after adding a few items to log).
>
> At first (top of list), it tries to find "Apple Lucida Grande" and  
> "Lucida Grande" with a particular "registry" and for the symbol  
> script.  This fails, because the `val' variable in  
> font_list_entities ends up being Qnil.

This is as expected.  The first query asks for fonts with  
family=Lucida Grande, that cover script=symbol.  The way the second  
criterion is handled is the issue.  ns_findfonts() has no idea whether  
the font is being requested just for some particular character or for  
rendering the script in general, so it tries to deliver a font that  
has "good coverage" of the requested script.  This is handled by  
ns_get_covering_families() for the script, which looks at the whole  
set of characters provided by the font and returns those that cover a  
certain percentage of the characters in the unicode range for the  
script.

I don't see what other behavior would be reasonable here.

Perhaps the 90% criterion (nsfont.m line 507) could be lowered; this  
might lead to other problems though -- I did experiment with this when  
setting it.  The best thing at this point might be to do a similar  
trace against X11 or w32 and see where things differ.  Of course, the  
available fonts will be different, so it is impossible to duplicate  
the conditions.