Mailing-List: contact users-help@pdfbox.apache.org; run by ezmlm
Precedence: bulk
Reply-To: users@pdfbox.apache.org
Content-Type: text/plain; charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\))
Subject: Re: Problems Using PDFBox To Manually Track TextPosition
From: John Hewson <john@jahewson.com>
In-Reply-To: <00d601d0d6ee$3bcaeea0$b360cbe0$@newconceptsdev.com>
Date: Sat, 15 Aug 2015 20:29:29 -0700
Content-Transfer-Encoding: quoted-printable
Message-Id: <5FA23B4F-3805-40BA-9C02-E513B2B89855@jahewson.com>
References: <00d601d0d6ee$3bcaeea0$b360cbe0$@newconceptsdev.com>
To: users@pdfbox.apache.org


> On 14 Aug 2015, at 17:06, John Walker <johnw@newconceptsdev.com> =
wrote:
>=20
> Hello,
>=20
>=20
>=20
> I'm using PDFBox to parse the contentstream for a page in a PDF.   =
Based on
> the list of operations, there are two lines of text that I expect to =
be in
> very different places on the page vertically.  However, when the page =
is
> displayed in Sumatra or Acrobat, this text is vertically aligned.

I=E2=80=99d recommend subclassing PDFStreamEngine if you want to hook =
into the PDF operators, specifically showTextString(s) and associated =
methods, such as showGlyph.

Parsing the stream yourself brings many challenges.

>=20
> The method I'm using to predict text position has been accurate in the =
past.
> I'm not sure if the method is faulty, or if I'm mis-understanding the
> operation list I'm getting from PDFBox.
>=20
>=20
>=20
> Here is the list of operations, with annotations explaining how I =
think they
> should impact vertical position of text cursor:=20
>=20
>=20
>=20
> http://pastebin.com/GUWWX3Kv
>=20
>=20
>=20
> As you can see, I'm basically only moving my model of the cursor in =
reaction
> to Tm's and Td's.  (TJ's aren't relevant because text is horizontal =
and the
> y position is the one I'm tracking.)   I also ignored the cm, because
> there's a Tm right after it.

You=E2=80=99re definitely misunderstanding the operators. Tm doesn=E2=80=99=
t set the x and y values, it specifies a matrix which is multiplied with =
the current Tm matrix in the graphics state. In addition, the graphics =
state itself can be saved/restored via the q and Q operators. You=E2=80=99=
ll also need to take the CTM into account (that=E2=80=99s the cm =
operator).

Anyway, don=E2=80=99t do that, use PDFStreamEngine instead.

=E2=80=94 John

>=20
> Am I mis-interpreting the PDF Operators (as I suspect)?  Is there any
> potential that this is a PDFBox issue? =20
>=20
>=20
>=20
> Thanks in advance!
>=20
>=20
>=20
> -John=20
>=20


---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@pdfbox.apache.org
For additional commands, e-mail: users-help@pdfbox.apache.org