Bidi paragraph direction in terminal emulators

Richard Wordingham via Unicode unicode at
Sat Feb 9 19:49:05 CST 2019

On Sat, 9 Feb 2019 18:42:52 +0100
Egmont Koblinger via Unicode <unicode at> wrote:

> The
> problem that I don't know how to address is: What if harfbuzz tells us
> that the overall width for rendering a particular grapheme cluster is
> significantly different from its designated area (the number of
> character cells [wcswidth()] multiplied by the width of each)?

You have to reduce the width of the glyph used.  The tricky bit is
where the glyph deliberately overhangs or underlies a neighbouring
glyph.  A good example of this is almost U+0E33 THAI CHARACTER SARA AM,
whose nikkhahit component can typically overhangs the previous
character; however, ink beyond the left limit should not be a problem
for LTR scripts. Which side do you align RTL cells on?

Now, you might want to treat U+0E33 as interacting with its
predecessor, because it does. The test word is น้ำ 'water'.


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