IDC's versus Egyptian format controls

[Richard Wordingham via Unicode]

On Fri, 16 Feb 2018 08:22:23 -0800
Ken Whistler via Unicode <unicode at unicode.org> wrote:

> On 2/16/2018 8:00 AM, Richard Wordingham via Unicode wrote:
> 
> > A more portable solution for ideographs is to render an Ideographic
> > Description Sequences (IDS) as approximations to the characters they
> > describe.  The Unicode Standard carefully does not prohibit so
> > doing, and a similar scheme is being developed for blocks of
> > Egyptian Hieroglyphs, and has been proposed for Mayan as well.  
> 
> A point of clarification: The IDC's (ideographic description
> characters) are explicitly *not* format controls. They are visible
> graphic symbols that sit visibly in text.

That doesn't square well with, "An implementation may render a valid
Ideographic Description Sequence either by rendering the individual
characters separately or by parsing the Ideographic Description
Sequence and drawing the ideograph so described." (TUS 10.0 p704, in
Section 18.2)

The reason for comparison with Egyptian quadrat controls is the scaling
issue.  The thickness of brush strokes should be consistent across the
ideograph, which increases the complexity of a font that parses the
descriptions.  Outline hieroglyphic quadrats have the same problem.
However, as I said before, there is a good argument for rendering an
IDS inelegantly.

Richard.