Re: decomposed and precomposde glyphs

[Hans Hagen <pragma@wxs.nl>]

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, 
for instance because fonts fonts not always provide a decompose (ccmp) 
or composed glyphs

(2) one can mess at the node list level which has a potyential drawback 
that one cannot get a character (explicit \char) there without the 
danger of it being mangled

so, whatever method one chooses, it has to be controlled because in tex 
all is about control (think of verbatim)

I have a file here that implements a pseudo feature that does this kind 
of (trivial) magic and I can add that to the distribution. (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).

Hans

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                                           Hans Hagen | PRAGMA ADE
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