Re: [XeTeX] Khmer: ligatures break if XeTeXlinebreaklocale is turned on

[Jonathan Kew]

On 10/04/2018 23:08, Jo Hund wrote:

Hi Jonathan,

Thank you very much for the helpful info. This fixed our problem with 
ligatures. All our formatting seems to be working, too.


However there are some problems if we insert "\\hspace{0pt}" anywhere in 
the document. In the worst case, the entire PDF conversion crashes, or 
in some situations, the ligatures are broken, and character spacing is 
off. We insert "\\hspace{0pt}" in combination with "\\nolinebreak[4]" in 
some places to coax Latex to break lines where we want them to break 
around some emdashes and other places. This is not a show stopper. We 
can work around it. We were just wondering if you may have an obvious 
solution to this.


I'm afraid I don't have any ideas about this. I'd normally expect 
inserting \hspace{0pt} to interrupt ligatures, but it shouldn't cause 
the job to fail altogether! That sounds like a bug.


If you can provide a test document where it causes a crash, we may be 
able to investigate further.


Thanks,

JK


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Re: [XeTeX] Khmer: ligatures break if XeTeXlinebreaklocale is turned on

[Jo Hund]

Hi Jonathan,

Thank you very much for the helpful info. This fixed our problem with 
ligatures. All our formatting seems to be working, too.


However there are some problems if we insert "\\hspace{0pt}" anywhere in 
the document. In the worst case, the entire PDF conversion crashes, or 
in some situations, the ligatures are broken, and character spacing is 
off. We insert "\\hspace{0pt}" in combination with "\\nolinebreak[4]" in 
some places to coax Latex to break lines where we want them to break 
around some emdashes and other places. This is not a show stopper. We 
can work around it. We were just wondering if you may have an obvious 
solution to this.


Thanks again for your help, much appreciated

Cheers

Jo




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Re: [XeTeX] Khmer: ligatures break if XeTeXlinebreaklocale is turned on

[Jonathan Kew]

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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