Proposal for BiDi in terminal emulators

Frédéric Grosshans via Unicode unicode at
Thu Jan 31 08:32:53 CST 2019

Le 31/01/2019 à 10:41, Egmont Koblinger a écrit :
> Hi,
>> Personally, I think we should simply assume that complex script
>> shaping is left to the terminal, and if the terminal cannot do that,
>> then that's a restriction of working on a text terminal.
> I cannot read any of the Arabic, Syriac etc. scripts, but I did lots
> of experimenting with picking random Arabic words, displaying in the
> terminal their unshaped as well as shaped (using presentation form
> characters) variants, and compared them to pango-view's (harfbuzz's)
> rendering.
> To my eyes the version I got in the terminal with the presentation
> form characters matched the "expected" (pango-view) rendering
> extremely closely. Of course there's still some tradeoffs due to fixed
> with cells (just as in English, arguably an "i" and "w" having the
> same width doesn't look as nice as with proportional fonts). In the
> mean time, the unshaped characters looks vastly differently.
>> OTOH a terminal emulator who wants to perform shaping needs
>> information from the application
> And the presentation form characters are pretty much exactly that
> information, aren't they (for Arabic)?
>> There's nothing you can do here [...] there's no way for the application to provide
> Instead of saying that it's not possible, could we perpahs try to
> solve it, or at least substantially improve the situation? I mean, for
> example we can introduce control characters that specify the language.
> We can introduce a flag that tells the terminal whether to do shaping
> or not. There are probably plenty of more ideas to be thrown in for
> discussion and improvement.
> cheers,
> egmont

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