# How to write a bounding box information in PostScript to an external file and read it in TeX at the second compilation?

## Scenario

• I want to create a new environment, e.g., pscanvas that does not need any size specification but just a unique filename. It can contain any graphic objects that pspicture can contain.

Thus

\begin{pscanvas}{<filename>}% no size specification needed
% any graphic objects go here
\end{pscanvas}


will simplify

\begin{pspicture}(<width>,<height>)% size specification needed as usual
% any graphic objects go here
\end{pspicture}


or

\begin{pspicture}(<x1>,<y1>)(<x2>,<y2>)% size specification needed as usual
% any graphic objects go here
\end{pspicture}

• Because the canvas size is not specified in the TeX input file, the TeX input file needs to be compiled at least twice.

The first compilation with latex->dvips->gs must produce a temporary file, for example, <filename>.bbi (bbi stands for bounding box info). This temporary file is generated on the fly by GhostScript when invoking PostScript code embedded in pscanvas.

The first compilation does not need to produce PDF output because the canvas size has not been properly prepared by TeX. However, if we produce PDF output, the PDF should render a notification box saying "Graphics is premature, please compile once more.".

The second compilation with latex, TeX engine reads the <filename>.bbi to make the exact space for the graphics filename. Compilation with dvips->ps2pdf then produces a final PDF output.

## Question

How to write bounding box information of the canvas in PostScript to an external file <filename>.bbi and read it from TeX world for preparing the canvas size?

• I will progressively give the first satisfying answer several bounties of various amount in installment until the total amount of the given bounties converges exactly to 5000 (five thousands). – kiss my armpit Feb 7 '14 at 2:05

I'm not sure of the requirements for reading the info back into TeX, but you can get the bounding box information from ghostscript formatted as a DSC comment.

gs -sDEVICE=bbox file.ps


This will print 2 lines to stderr in response to each showpage event.

%%BoundingBox: 51 93 511 731
%%HiResBoundingBox: 51.335998 93.131997 510.209984 730.061978

%%BoundingBox: 23 83 587 765
%%HiResBoundingBox: 23.147999 83.087997 586.331982 764.801977


(The extra blank line was when I hit enter for the invisible showpage prompt. Invisible because I redirected stdout to get a nice picture of stderr.)

To capture it in a file, we need to wrangle the stderr handle.

gs -sDEVICE=bbox file.ps 2>file.bbi


Some other useful options are -dBATCH: exit after the file (otherwise it goes to a PS> prompt), and -dNOPAUSE: do not wait for enter at showpage.

If we can control how the shell-out to gs is handled, it might be possible to pipe the postscript fragment without an additional intermediate file.

??? | gs -q -sDEVICE=bbox -dNOPAUSE -dBATCH - 2>&1 | ???


This assumes the postscript program makes no interfering text output of its own.

• That is not possible from within TeX. – user2478 Feb 15 '14 at 21:26
• Rats... It may be possible to select the bbox device from within the postscript program. I'll have to do some research. But if we can't redirect stderr, ... Hm.... – luser droog Feb 16 '14 at 3:43
• @Herbert: If LaTeX can read the auxiliary files (.aux, .log, etc) at the second compilation, it should be possible for LaTeX to read the bounding box info (.bbi) at the second compilation as well. :-) – kiss my armpit Feb 16 '14 at 5:33
• @luserdroog: You have to run dvips and then gs on a file which doesn't exist in the current TeX run. It is only possible with another TeX source or with a script. But that is already possible. – user2478 Feb 16 '14 at 6:27
• Hm. I see, so we're either looking at 3-pass compilation, or maybe piping into gs? The option - indicates to execute stdin. – luser droog Feb 16 '14 at 6:37