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Subject: Re: Character widths
From: John Hewson <john@jahewson.com>
In-Reply-To: <CA+YcCwqAymRbWLpxnXadsuxbe0ETE_X_DB8yq_42-=bk2HrTuw@mail.gmail.com>
Date: Mon, 1 Aug 2016 14:51:01 -0700
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Message-Id: <DEBCCF53-FB04-4725-A6BD-FE638048F9EB@jahewson.com>
References: <CA+YcCwphfYYN8SK-6e=NTLcS_MZXj7Bi748A7fq1_N4UqaAzsA@mail.gmail.com> <90996F3C-E8B4-4DFD-A08F-830B0400F791@jahewson.com> <CA+YcCwqAymRbWLpxnXadsuxbe0ETE_X_DB8yq_42-=bk2HrTuw@mail.gmail.com>
To: users@pdfbox.apache.org
archived-at: Mon, 01 Aug 2016 21:51:09 -0000


> On 1 Aug 2016, at 14:12, Aaron Mulder <ammulder@gmail.com> wrote:
>=20
> On Mon, Aug 1, 2016 at 2:23 PM, John Hewson <john@jahewson.com> wrote:
>> That=E2=80=99s correct. getStringWidth is for use when creating new =
PDFs only, and we don=E2=80=99t
>> implement kerning, so the width you get will be =E2=80=9Ccorrect=E2=80=9D=
 with respect to the text
>> in the newly created PDF.
>=20
> So, I guess I don't understand this part.
>=20
> My impression was that if you wrote something like "/Helvetica 12 Tf
> (AVAVAV) Tj" to the PDF document, a reader displaying the document
> would use the standard-14 Helvetica font to draw the string "AVAVAV"
> to the screen, and because that font implements kerning for those
> character combinations, the reader would display the text as more
> compressed horizontally than in the absence of kerning.

No, PDF is rather unusual in this respect. Any kerns have to be =
specified
manually in the Tj array. The idea being that the PDF renderer is a =
=E2=80=9Cdumb=E2=80=9D
client:

e.g. "AWAY again=E2=80=9D with A-W-A kerned:

[ (A) 120 (W) 120 (A) 95 (Y again) ] TJ

See p251 of ISO 32000 for more details.

=E2=80=94 John

> So my expectation is that if you did the commands above and then drew
> a box around it using the horizontal dimension provided by
> getStringWidth("AVAVAV"), your box would display as slightly larger
> than the visible text width due to the absence of kerning in
> calculating the box size based on the text width at the time you wrote
> the document, but the presence of kerning in rendering the text in the
> reader.
>=20
> Where am I going wrong there?
>=20
> Thanks,
>       Aaron
>=20
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>=20


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