[DVIPDFMx] /Rect [...] of pdf annotation too big

[Alexander Grahn]

Hi,

I noticed that annotations in PDFs created with dvipdfmx are by 2 bp
larger in each direction than specified in the pdf-special `annot'.

Here is a minimal example:

\ifx\pdfoutput\undefined
  \special{pdf:annot width 10bp height 5bp depth 5bp <<
    /Type/Annotation /Subtype/Link /H/I
  >>}%
\else%
  \ifnum\pdfoutput=1
    \pdfannot width 10bp height 5bp depth 5bp {%
      /Type/Annotation /Subtype/Link /H/I
    }%
  \fi%
\fi%
\bye

When run through TeX/dvipdfmx, an annotation with

  /Rect [71 763.82 83 775.82]

is produced. It has an extension of 12bp instead of 10 bp in each
direction.

On the other hand, pdftex produces a 10bp by 10bp annotation, as expected:

  /Rect [72 764.89 82 774.89]

In the case of my animate package, where I put widget annotations tightly
together in a row in order to create animation controls, this leads to
overlapping buttons if the dvipdfmx route is taken.

Where does dvipdfmx define the extra amount to be added to the size
arguments of the  pdf:ann special? Is there a way to retrieve this value
from within TeX, e. g. from some \dimen register?

Thanks for your advice,

Alexander