Re: PDF

[Valeriy E. Ushakov]

On Tue, Dec 02, 1997 at 11:49:09AM +1100, Darrin Smart wrote:

> Valeriy E. Ushakov wrote:
>
> > And a rudimentary PDF backend without all the bells and whistles can
> > share a lot of code with PS backend.  I think 99.9% of engine code can
> > be shared as the imaging model is the same, the differences are in the
> > output format.
>
> It would be a little more complex than this. A lot of the PostScript
> specifics are actually in the package definitions. You also need to grep
> for @BackEnd in these. And actual postscript functions are defined in
> some of these too.

Yes, I intentionally oversimplified the problem :-)


> In addition, if PDF is a binary format it could be rather difficult
> to write packages to output them.

PDF 1.0 was ASCII only.  PDF 1.1 specification states (I have 1.1 spec
in text, I have 1.2 spec in PDF only, so I can't paste from it from
home):

| A PDF file is either a 7-bit ASCII file or a binary file.  If it is
| a 7-bit ASCII file, only the printable subset of the 7-bit ASCII
| code plus space, tab and newline (return or linefeed) is used.  If
| it is a binary file, the entire 8-bit range of characters may be
| used.

PDF backend can stick to producing plain ASCII.  A separate converter
can (can it?) later be used to convert PDF output from Lout into
binary format, to apply encription etc.


> Or you could write a XML-based specification for the backend which used
> a declaritive drawing model rather than a programming language which
> would make writing filters to various formats easier.

Hmm, sounds like SPDL, isn't it?

SPDL is ISO Standard Page Description Langauge which is a mixture of a
subset of PostScript structured with SGML.  Check the SGML Page at
http://www.sil.org/sgml/sgml.html and go to "related standards"
sections.

SY, Uwe
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