[NTG-pdftex] [pdftex-Bugs][4302] transparency bug: missing /ExtGState in Resources of Form XObject

pdftex-bugs at sarovar.org pdftex-bugs at sarovar.org
Wed Jan 20 10:44:01 CET 2010


Bugs item #4302, was opened at 2010-01-18 17:32
Status: Open
Priority: 3
Submitted By: Alexander Grahn (grahn)
Assigned to: Nobody (None)
Summary: transparency bug: missing /ExtGState in Resources of Form XObject 
Category: None
Group: None
Resolution: None


Initial Comment:
In the attached example a Form XObject is created from a savebox containing transparent objects. The Form XObject is later used by \pdfrefxform\pdflastxform. When loaded in AR-7, the resulting PDF cannot be displayed but causes the error message:
                                             
  Could not find the Extended Graphics State named 'pgf at CA0.5'.

(AR-7 is more verbose with regard to PDF errors.)                                       

The reason is that the XObject produced is broken. At some point in the content stream of the XObject, the graphics state is modified to set the transparency of subsequent fills and strokes:

/pgf at CA0.5 gs                                                                   /pgf at ca0.5 gs                                                                           

Although the operands pgf at CA0.5 and pgf at ca0.5 are defined in an ExtGState Dictionary as 

1 0 obj                                                                            
<< /pgf at CA0.5 << /CA 0.5 >> /pgf at ca0.5 << /ca 0.5 >>>>                                  
endobj                                                                                        
the corresponding /ExtGState key is missing in the Resources dictionary of the XObject. Instead, it is put to the Resources dictionary of the Page object.  But there it is useless, because it is not used in the content stream of the page.

pdfTeX-Version: 1.40.10

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Comment By: Alexander Grahn (grahn)
Date: 2010-01-20 10:44

Message:
After all, it is not a pdftex bug. I found out that PGF/TikZ adds resources such as /ExtGState and /Pattern, used in the graphics, to the /Resources dict of the /Page object. In order to make such resources accessible to the graphics encapsulated in a Form XObject too, one has to once more add a reference to the /Resources dict, this time to the Form XObject to be created, by means of the `resources {...}' argument of \pdfxform. See the attached example file `transs_ok.tex'.

I think this bug can be closed. Sorry for the noise.

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