From: Mark Davis (mark.davis@icu-project.org)
Date: Tue Aug 28 2007 - 11:20:41 CDT
On 8/28/07, James Kass <thunder-bird@earthlink.net> wrote:
>
>
> Mark Davis wrote,
>
> > And the CJK VS characters should never be visible
> > in a font that has CJK characters.
>
> "...in a font that has CJK characters." This is an important point.
>
> The developer would be well advised to include some kind of glyph
> for VS characters, but only if the font being designed supports
> base characters which can combine with VS characters in valid
> sequences.
>
> In other words, a font not designed to support math characters
> and which does not support VS characters would be expected to
> display two little boxes for a valid string consisting of a math
> base character plus a VS character.
>
> If the font supports VS characters for any other sequences, but
> does not support math characters, and the font uses control
> picture glyphs for VS characters, then the above string would
> display as a little box plus the control picture for the VS. If
> this font instead maps zero-width no-contour glyphs with VS
> characters, then the display will just be one free standing little
> box.
>
> Please note that the above rendering descriptions represent the
> way things actually work right now, rather than being an opinion
> concerning optimal performance. I do think, though, that things
> are working just fine.
>
> Because of the various possible factor combinations, the font
> developer should retain control of font character coverage.
>
> And, I just can't seem to leave this alone...
>
> > And the CJK VS characters should never be visible
> > in a font that has CJK characters.
>
> ...except during input/editing, if the font designer so desires
> and designs accordingly. In this case, though, the display of
> an invalid or unsupported (by the font) sequence would result
> in a display of a control picture rather than being transparent
> to the reader. Font designers can be well aware of this, yet
> choose to use control pictures anyway.
No. This is the core of the problem. If an application wants to Show Hidden,
and reveal VS characters, it can have a special rendering mode to do so,
where it replaces DI and whitespace by pictures. And it will have to manage
the pictures because it can't depend on any fonts to do it.
The font should always have invisible CJKVS characters if it has CJK
characters: otherwise it screws up normal rendering. The NORMAL rendering of
a CJK character plus CJKVSn, if the pair is not supported by the font, is
the CJK character alone. Period. No gummed up box after it.
Best regards,
>
> James Kass
>
>
>
-- Mark
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