Re: decomposed and precomposde glyphs

[Ulrike Fischer <news3@nililand.de>]

Am Thu, 23 Feb 2017 13:19:12 +0100 schrieb Hans Hagen:

> On 2/23/2017 11:58 AM, Ulrike Fischer wrote:
>> When using input like the following with xetex then harfbuzz kicks
>> in and one would always get the good looking precomposed U+1EA0 for
>> the A and the decomposed B+U+0323 for the B.
>>
>> With context (and lualatex) one get a rather bad looking -- as the
>> dot is misplaced -- output for the A^^^^0323 input and no output at
>> all for ^^^^1e04.
>>
>> As the coverage for precomposed glyphs varies a lot across fonts
>> this is rather a nuisance.  Is there a way to get the fontloader
>> (also the one used by luaotfload) to do a similar substituation as
>> done by harfbuzz?
>>
>> \starttext
>> \catcode`\^= 7
>> Ạ A^^^^0323  %decomposed input -> U+1EA0 with xetex
>>
>> Ạ  ^^^^1ea0  %precomposed input
>>
>>
>> Ḅ B^^^^0323  %decomposed input
>>
>> ^^^^1e04     %precomposed input -> B+U+0323 with xetex
>>
>>
>> \stoptext
>>
>>
>> (I added the ^^-notation to avoid problems with copy&paste)
> 
> In context one can enable a collapse (last week i found out that it was 
> off by default).
> 
> Anyway, there are two issues here:
> 
> (1) one can in the input stream collapse the dot accent and the other 
> character but of course an altered input might not be what one wants,

No changing the input is imho not a solution as the document fonts
can have different coverage of the glyphs. Whatever is done must be
font dependant. 

> (btw, I suppose that xetex can disable that on demand as from your
> post I deduce that it's default behaviour and fighting defaults
> is a pain).

I don't think that one disable the behaviour in xetex, the internal
harfbuzz library is doing it. There is imho no way to get a
A+combining accent in a document.

I agree that it would be neat to be able to disable it but on the
whole: if I had only the choice between "the xetex-substituation"
and the current luatex/context behaviour I would prefer the first.
For normal documents it is preferable. 

Did you sent the second mail only for me for a reason or did you
only forget to add the list? Imho this is interesting for others
too. 


-- 
Ulrike Fischer 
http://www.troubleshooting-tex.de/

___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________