[poppler] Vertical or horizontal writing?

[cobra.yu]

Hi,

     The original requirement to detect the direction of text flow is for "searching". The present "search" function of Poppler::Page is searching horizontally only. So, for CJK users, I must add one vertical search function for the vertical writing mode.
     I could sort out all the textboxes in every page by (x,y) of the bounding box to make a vertical-like textbox list, but I encountered a fundamental problem: If I can't know the exact direction of text flow first, how could I know when to use vertical or horizontal search?
     BTW, I've accomplished the vertical text selection by the same way as my vertical search right now, but it's rather simpler than searching indeed.

          Cobra

              
-----Original message-----
From:mpsuzuki at hiroshima-u.ac.jp
To:Deri James <deri at chuzzlewit.demon.co.uk>
Cc:poppler at lists.freedesktop.org,cobra.yu at hyweb.com.tw
Date:Wed, 28 Jul 2010 01:59:40 +0900
Subject:Re: [poppler] Vertical or horizontal writing?

Dear Deri,

On Tue, 27 Jul 2010 17:22:14 +0100
Deri James <deri at chuzzlewit.demon.co.uk> wrote:
>When looking at the two PDFs you are using with acroread using the text 
>selection tool:-
>
>P1 of 'vert-horiz-ipa-std.pdf' selection caret is drawn horizontally.
>'msword2010-vert2.pdf' selection caret is drawn vertically.
>
>So, it seems acroread can't detect the vertical text in this file, i.e. it is 
>actually horizontal text placed one glyph at a time (apart from 'MS Word 2010' 
>which is horizontal text rotated 90 degrees).
>
>The contents of the stream confirms this:-
>
>stream
> /P <</MCID 0/Lang (en-US)>> BDC BT
>/F1 10.56 Tf
>0.000000001 -1 1 0.000000001 496.54 756.84 Tm
>0 g
>0 G
>[(MS)6( )5(W)61(ord)-4( )5(20)10(10)] TJ
>ET
> EMC  /P <</MCID 1>> BDC BT
>/F2 10.56 Tf
>1 0.000000017 -0.000000017 1 495.29 673.7 Tm
><085B>Tj
>ET
> EMC  /P <</MCID 2>> BDC BT
>1 0.000000017 -0.000000017 1 495.29 663.14 Tm
><29AA>Tj

>...
>
>So this PDF does not have any true vertical text.

Yes, yes, just I've reached exactly same conclusion.
Thank you for checking the content of PDF.

The PDF generated by MS Office addin uses the font object
for horizontal writing mode, in PDF design, at least. So
the text flow detection in PDF font level does not work
with such PDF. Higher level recognization is needed.

It brings a philosophical question: what is vertical text?
Some people makes vertical serie of CJK glyphs by using
very very narrow text box, is this wrong vertical text?
If they are not vertical text, why we should distinguish?
The invalid shape of the punctuations & arrows? Or...

I have to ask Cobra about what is the original requirement
why the text direction should be detected. Cobra, could
you describe why you needed to detect the direction of
text flow?

Regards,
mpsuzuki