Bidi paragraph direction in terminal emulators

[Richard Wordingham via Unicode]

On Fri, 08 Feb 2019 11:34:29 +0200
Eli Zaretskii via Unicode <unicode at unicode.org> wrote:

> > Date: Fri, 8 Feb 2019 06:40:44 +0000
> > From: Richard Wordingham via Unicode <unicode at unicode.org>
> >   
> > > I, for one, am not to the slightest bit interested in abandoning
> > > the character grid and allowing for proportional fonts. This
> > > would just break a gazillion of things.  
> > 
> > The message I take from that and this thread in general is that
> > Emacs and 'M-x term' are the route to take if one only has
> > proportional fonts.  
> 
> Not sure why.  There are terminal emulators out there which support
> proportional fonts.  Emacs is perhaps the only one whose terminal
> emulator currently supports bidi more or less in full, but is that
> related to proportional fonts?

Emacs is the one I know that can be made to support Indic fonts.  It's
rather a big too for such a relatively minor task, which is why I
implicitly called it a sledgehammer.

> > What's the sledgehammer for Windows?  

> Not sure what you meant.  "M-x term" doesn't work on Windows.

So my question is, 'What do I use on Windows?'  The application may be
disproportionate to the function I use it for.

> > Where do I find the specification for fixed-width fonts (is
> > wcswidth() the core?) and how do I select the set of fonts to use?
> > Do I need to use fontconfig where available?  

> That depends on the underlying C library and other facilities;
> basically on your OS.  AFAIK wcwidth will give the results consistent
> with the UCD only if you use glibc.  In Emacs, you have the functions
> char-width and string-width that take their data from
> EastAsianWidth.txt.  Not sure about other facilities, and I don't
> really understand what environment are you asking about -- are you
> talking about C/C++ programs?

I will give a concrete application.  If I want to make a font that is
interpretable for Tai Tham and maximally usable with VTE, what are the
VTE-specific constraints for me to be able to use it for Tai Tham when
using basic text utilities?  For example, if VTE decides that for
<cons, left-matra, above-matra> as two clusters <cons> and <left-matra,
above-matra>, can I nevertheless position the above-matra above the
<cons>?

Richard.