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From: Aaron Madlon-Kay <aaron@madlon-kay.com>
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Subject: Re: Creating vertical text
Date: Sun, 12 Nov 2017 21:46:37 +0900
References: <3723506D-D663-4EB6-832F-AC052EDC230B@madlon-kay.com>
To: users@pdfbox.apache.org
In-Reply-To: <3723506D-D663-4EB6-832F-AC052EDC230B@madlon-kay.com>
Message-Id: <6B56DF9E-F9F4-413F-B104-0B6132D41987@madlon-kay.com>
archived-at: Sun, 12 Nov 2017 12:46:50 -0000

I received some spot-on advice from PDFBox contributor John Hewson, so I =
wanted to share it in case anyone else has the same issue:

> John Hewson wrote:
>=20
> =E2=80=A6
>=20
> First of all, Identity-V seems like the right approach. PDFBox should =
be able to handle the basics of vertical text layout using that. =
However, as you say advanced OpenType features such as GSUB are not =
supported in PDFBox. That=E2=80=99s because OpenType is not supported in =
PDF* as it=E2=80=99s too new. So it=E2=80=99s up to the program/library =
which generates the PDF to apply the positioning or substitution itself =
and place the correct glyph on the page. PDFBox doesn=E2=80=99t =
implement that functionality, because it=E2=80=99s pretty complex - =
though we=E2=80=99d certainly like to!
>=20
> * not entirely true, but PDF viewers have very limited support for it.
>=20
> The way OpenType Layout works is that there are various abstract =
"features=E2=80=9D which are identified by =E2=80=9Ctags=E2=80=9D such =
as =E2=80=9Cvert=E2=80=9D. These are simply used as keys to turn on/off =
various positioning or substitutions, which can be found in the GSUB and =
GPOS tables, respectively. So when an application wants, say, the =
vertical version of a font, it enables the =E2=80=9Cvert=E2=80=9D =
feature by applying all the relevant substitutions/positionings. This =
could be as simple as a substitution rule which switches a horizontal =
glyph for a vertical one, or a complex state machine for some Indic =
language. In the case of =E2=80=9Cvert=E2=80=9D, it=E2=80=99s going to =
be the former.
>=20
> Given that GSUB and GPOS support are not coming to PDFBox anytime soon =
and assuming that you are just wanting to use a limited set of vertical =
fonts then I=E2=80=99d recommend =E2=80=9Cfreezing=E2=80=9D the =
=E2=80=9Cvert=E2=80=9D feature into the font. This means creating a =
special subset of the font which already has the positioning and =
substitutions applied to the glyphs themselves. The resulting font =
won=E2=80=99t have any need for GSUB or GPOS tables for =E2=80=9Cvert=E2=80=
=9D any more, and will only support vertical writing. You can find a =
tool for generating such fonts here: =
https://github.com/twardoch/fonttools-utils/tree/master/pyftfeatfreeze
>=20
> For debugging, if you=E2=80=99re looking for a tool to inspect the =
table inside fonts, I recommend the free DTL OTMaster Light available =
here: http://fontmaster.nl, Microsoft=E2=80=99s OpenType spec is also =
helpful: =
https://www.microsoft.com/en-us/Typography/OpenTypeSpecification.aspx


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