🚀 go-pugleaf

matt@EECS.NWU.EDU (Matt Larson) writes:

>I am interested in writing a filter that can count the number of pages
>printed to an HPLJ II.  The input stream could be plain text or the HP
>graphics language.  Counting pages of text is easy; counting pages of
>graphics (for example, output from Ghostscript, gnuplot, dvijep, etc.)
>is the part that has me stumped.

>Is there a sequence that always means, ``End of the page; print it''?
>I thought that's what the formfeed character (ASCII 12) did.  I tried
>counting formfeed characters, but that doesn't seem to work: there are
>way too many.  My current guess is that the formfeed character really
>means what I think it means, but that it is also possible for
>formfeeds to be part of other commands or in some sort of "quoted
>string."  If I am on the right track, then the question is: How do I
>tell the real formfeeds that mean end of page from the other ones?

You're right; FF is the all-done-now-print order, but only if it is
received in a protocol context.  The bit pattern (x'0C') can also appear
in any of a number of binary data fields, either for graphic images
or in a font download.

I suspect that you'll have to write code to parse all of the PCL sequences
in much the same manner that VT-100 emulators have to parse its escape
sequences, even if you don't do anything with them.  I don't have the
book handy, but there are many PCL sequences of the form:

  <ESC> <operation> <character count> <binary data>

which you'll have to recognize and skip over without testing for the
presence of a form-feed command.

Joe Morris