Marcel Fabian Krüger tex at
Tue Oct 15 14:15:19 CEST 2019

Hi Norbert,

On Tue, Oct 15, 2019 at 05:32:49PM +0900, Norbert Preining wrote:
> Hi Ulrike,
> thanks for your email, it would be great if we could work that out, I am
> helping a friend settting Tibetan/Sanskrit texts and this is a real
> pain.
> I attach four files
> 	tibetan-test.ENGINE.pdf
> for ENGINE in luatex, xetex, luahbtex, harftex
> * First of all, the text you send does not show up correctly with
>   luatex, only with xetex, there is considerable overlap in glyphs
>   and the wrong compound is selected in the luatex and luahbtex case.
> * Then look at the first row of big characters
>   - xetex got it correct with all fonts
>   - lua(hb)tex use a strange glyph with a dotted circle set below, 
>     in the Noto case

I tried this with the current development branch for the HarfBuzz
support in luaotfload and got the same output as with XeTeX, so
luahbtex will be able to solve this issue.

> * The last line shows the biggest problem: In Tibetan there are
>   "standard" combinations of characters, that are used in normal
>   Tibetan, and then there are non-standard ones, that are often
>   used to transcribe religious text, Devenagari etc etc. If the font
>   does not provide a proper pre-composed glyph, the font/layout
>   engine needs to do this manually.
>   Back in Omega times I wrote code for this in OTPs (analyzing
>   the stacks, and emitting TeX code creating the proper stacks),
>   but with xetex and luatex the layout is completely broken.
>   In the xetex case we even get the dotted circle variants set
>   aside ..

These look like problems with the fonts, do they work better in other
programs? Especially the dotted circles in Noto Tibetan was a known bug
which is fixed in current versions. Related to this: The font
"Noto Sans Tibetan" has been renamed to "Noto Serif Tibetan" so the
"Sans" file hasn't been updated in recent years.
If I try your example with "Serif", I get a glyph which looks quite
similiar to your picture. (I attached the PDF file)

Best regards,

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