On 10/04/2018 16:55, Jo Hund wrote:
Hi there,
I was told by David Carlisle on https://tex.stackexchange.com that the
xetex mailing list may be a good place to ask my question:
When generating documents in Khmer, we noticed that some ligatures do
not work. We found that turning off XeTeXlinebreaklocale fixes all
ligatures, however this causes problems with linebreaks, and lines
extend past the right margin if there aren't any zero width spaces
between words. (In Khmer words within the same sentence or phrase are
generally run together with no spaces between them.)
Our objective is to have all ligatures work, and to use
XeTeXlinebreaklocale at the same time.
Please note that we are not looking for a manual workaround for this
particular example. We are looking for a fix to the root cause that we
can then use in our automated system where we cannot fix individual
instances of this problem.
The problem arises because activating XeTeXlinebreaklocale effectively
makes xetex insert something like \penalty0 or \hskip0pt or similar
(depending on the settings of \XeTeXlinebreakpenalty and ...skip) at
each potential line-break position, so that the normal TeX line-breaking
algorithm will be able to find and use these breaks.
But the inserted penalty and/or skip interrupts the sequence of
characters that is passed to the OpenType shaping engine, and so
features like ligatures will not work across the boundary.
A possible workaround would be to set \XeTeXinterwordspaceshaping=2 in
your document. This will cause xetex to re-shape runs of text after
line-breaking, and at this point your ligatures should work.
There are some caveats: in particular you'll notice if you try this that
your red coloring of the example text fragment gets lost. This is
because the \special{}s that \color inserts will be moved out of the run
of text that is now being shaped as a unit. But depending on the needs
of your documents, this may be an acceptable trade-off.
Oh, by the way: you can change the \XeTeXinterwordspaceshaping setting
within the document if you like, but its effect does not respect the
usual TeX scoping rules; if I remember correctly,
\XeTeXinterwordspaceshaping=2 basically operates on a whole-page basis,
so what matters is the value at the time the page is completed.
HTH,
JK
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