[HarfBuzz] Don't render control characters?

[Konstantin Ritt]

2014-03-06 21:32 GMT+02:00 Richard Wordingham <
richard.wordingham at ntlworld.com>:

> On Wed, 05 Mar 2014 15:04:30 -0800
> Behdad Esfahbod <behdad at behdad.org> wrote:
>
> > Any objection to not rendering Unicode GC=Cc, same way that we don't
> > render Default_Ignorables?
>
> I'm not sure that BS (U+0008) and TAB (U+0009) don't need to be
> rendered.  I can imagine a terminal emulator wanting BS for
> overstriking, and having no spacing for TAB is suboptimal.  TAB can
> easily get into text to be rendered.
>
>
Did you meet any single font with glyph for U+0008 (BS)? Honestly, I don't
imagine what U+0008 glyph representation looks like :)
GC=Cc aren't really a characters but a control codes; some of them are
historically very common in use, though.

As for TAB, certain fonts don't have nbsp and/or tab, and most fonts don't
have line separator, paragraph separator, and many other space characters.
Since we've touched this topic...in my opinion, HarfBuzz should take care
of (quite common) issue with missing glyphs for characters of property
White_Space [1].
For any of them, a fallback to U+0020 (SPACE) should be enough [2], though
a more sophisticated mechanism would also take care of glyph advances [3],
making U+000A..U+000D, U+0085, U+2028..U+2029 occupy no space, U+202F
occupy "narrow" space, and simply dub U+0020 metrics for other space
characters.
I'll make a patch if Behdad (or maybe someone else) would +1 to this
proposition.

[1] http://www.unicode.org/Public/6.3.0/ucd/PropList.txt
[2] http://www.unicode.org/faq/unsup_char.html#2
[3] http://www.unicode.org/faq/unsup_char.html#5
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