[HarfBuzz] Don't render control characters?

Konstantin Ritt ritt.ks at gmail.com
Thu Mar 6 16:13:45 PST 2014

2014-03-07 1:20 GMT+02:00 <mskala at ansuz.sooke.bc.ca>:

> On Thu, 6 Mar 2014, Richard Wordingham wrote:
> > On Thu, 6 Mar 2014 22:38:07 +0200
> > Konstantin Ritt <ritt.ks at gmail.com> wrote:
> >
> > > Did you meet any single font with glyph for U+0008 (BS)? Honestly, I
> > > don't imagine what U+0008 glyph representation looks like :)
> >
> > Back one space!  The underlining in Unix man pages is usually
> > implemented as overstrike via U+0008.  However, I'd forgotten that
> > OpenType advance widths can't be negative, so it can't be rendered
> > under font control.
> ECMA-17, or ISO 2047, is now withdrawn, but it specified a graphical
> symbol for the control character we now call U+0008.  The symbol
> looked like an arrow running from lower right to upper left, with a
> slight concave-downward curve.  You can find a copy of the document here:
> http://www.ecma-international.org/publications/files/ECMA-ST-WITHDRAWN/ECMA-17,%201st%20Edition,%20November%201968.pdf
The p2. "PURPOSE" states almost literally the same what I was describing by
> 2) A "show document structure" rendering option, where some normally
invisible characters are handled by a special font (i.e. to visualize some
control characters, BiDi format characters, objects, etc.)
This is a use-case I do care about, too.

Perhaps we'll need a separate flag to be able to choose between "hide
<GC=Cc>" and "hide <GC=Cc> iff not present in the font".
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