Op 2/08/2012 12:17, Robert Bowen schreef:
I have a ballot with a bunch of different contests (President,
Vice-president, etc.) each with its candidates. Next to each candidate
is an oval. I'd like to use iText to check a given oval for each contest.
The ovals are not within an AcroForm, and they are not checkboxes. I
opened my pdf with Acrobat and selected a random oval and they seem to
be just normal objects ... perhaps graphic objects, I'm not sure, I
couldn't tell.
I used a combination of PDFReader, PDFStamper and Document to
uncompress the PDF, to be able to edit it in a normal text editor, and
it seems that each oval looks something like this:
01 g
89.04 650.52 41.22 24 re
f
1 J 1 j 0.2 w 10 M
1 i
116.28 662.58 m
116.28 664.56 112.44 666.12 107.7 666.12 c
102.96 666.12 99.12 664.56 99.12 662.58 c
99.12 660.6 102.96 658.98 107.7 658.98 c
112.44 658.98 116.28 660.6 116.28 662.58 c
b*
and if I manually add a '0 g' between '1 i' and '116.28 662.58 m', it
marks the oval. But if I write a program in Java to do this, to add '0
g' for each oval, the resulting PDF is corrupt, because ... well, you
can't just edit a PDF like that, you have to update the stream, the
dictionary, etc.
The path of the oval is defined using one moveTo (m) and four curveTo
(c) operators.
The path is drawn using a closePathEoFillStroke command (b*).
Close path means: add a path between start and end point if the curves
don't form a closed shape
Eo means: use the Even-Odd algorithm to find out which areas need to be
filled.
Fill means: fill the shape using the fill color
Stroke means: draw the borders using the stroke color
The fill color is defined with the g operator: 01 is the gray fill value
(0 is black, 1 is white).
The line width is 0.2 user units (w), but I don't see any operator
defining the stroke color (maybe it's just the default: black).
If you manually add "0 g" after "2 i", then the fill color will be
black, but you need to be very careful when doing so.
If you're sure about the PDF syntax, then this is a code sample I used
to change the content of a form XObject.
I'm sure you can adapt it to change the content stream of the page:
// read file my.pdf
PdfReader r = new PdfReader("my.pdf");
// get page dictionary of page 1
PdfDictionary p = r.getPageN(1);
// get the resources
PdfDictionary ps = p.getAsDict(PdfName.RESOURCES);
// get the XObjects
PdfDictionary xo = ps.getAsDict(PdfName.XOBJECT);
// get the content stream of a specific XObject identified by key
PRStream stream = (PRStream)xo.getAsStream(key);
// change its content (in this case: empty the content)
stream.setData(new byte[]{});
// create a new (altered) PDF
PdfStamper stamper = new PdfStamper(r, new FileOutputStream("new.pdf"));
stamper.close();
With this code, the structure of your PDF will not be corrupted.
However: if you use the wrong bytes, you can corrupt the content of a page.
Reading the syntax snippet however, I have the impression you know what
you're doing.
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