Re: Progress on xterm with combining characters, wcwidth

[Markus Kuhn <Markus.Kuhn@cl.cam.ac.uk>]

Bruno Haible wrote on 1999-11-29 15:09 UTC:
> Markus posted such a function. Except that you should call it "isnonspacing",
> not "iscombining": It covers the "Non-spacing" property of PropList.txt [5].
> Note there are also combining characters with a width of 1. The first one
> is U+0903. All of them are in Indic scripts. How are they supposed to be
> rendered by a simple rendering engine as xterm?

Probably not at all. I think, supporting Indic scripts would mean
stretching the typewriter model behind the VT100 terminal far too far.
We really should leave Indic script text processing for the moment to
GUI applications (GTK i18n, X11R7, etc.) that have pixel access to the
screen and can bypass the text rendering mechanisms of the system. Don't
worry about Indic scripts in UTF-8 VT100 terminal applications. The
glyphs aren't available in the commonly used fonts anyway.

Just treat the Indic spacing combining characters as normal spacing
characters, because they will anyway be represented under xterm together
with all other Indic characters with the DEFAULT_CHAR box.

If you really want to get into the adventurous area of ligature
substitution in a terminal emulator, then better first start with
Arabic, where there is at least some consensus on what exactly the
ligatures are and how they are to be encoded.

Let's get support for all the European and CJK scripts first widely
deployed for terminal applications, before we think about adding even
more burden to the implementor with Arabic and especially Indic.

Markus

-- 
Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at acm.org,  WWW: <http://www.cl.cam.ac.uk/~mgk25/>

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