[XeTeX] inconsistant kerning

[Jonathan Kew]

On 27 Sep 2006, at 2:58 pm, Jonathan Kew wrote:

> On 27 Sep 2006, at 2:07 pm, Malte Rosenau wrote:
>>
>>  I've also noticed a strange case of kerning
>> in the german abbreviation 'Vf.'
>>
>> \font\1="Minion Pro" at 12pt
>> \1 Vf. Va
>> \bye
>>
>> Gives me too much negative kerning in 'Vf.', while the 'Va' is
>> perfectly OK.

This turns out to be related to a previous problem where a string  
such as "AVAVAV" was not kerned correctly; you'd get kerning only  
between every other pair of letters, not every pair. I tried to fix  
this back in June, but didn't understand the ICU code involved  
properly, and this new bug was a side-effect of my incorrect patch.  
It no longer skipped certain glyph pairs, but instead it could overdo  
the kerning (as seen here) in certain cases, depending on the  
construction of the GPOS lookups in the font.

A new fix -- which I believe is correct this time! -- is in the XeTeX  
repository rev. 375; if some people would like to check out and build  
the new code, it would be good to test it with a range of OpenType  
fonts that include the 'kern' feature. (Looks OK so far with those  
I've tried.)

JK