IDC's versus Egyptian format controls

[Asmus Freytag via Unicode]

On 2/16/2018 10:20 AM, Richard Wordingham via Unicode wrote:
> 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)

Should we ask t make the default behavior (visible IDS characters) more 
explicit?

I don't mind allowing the other as an option (it's kind of the reverse 
of the "show invisible"
mode, which we also allow, but for which we do have a clear default).
>
> 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.
>