Re: [Groff] PDFPIC macro

[Ted Harding]

On 21-Sep-2014 10:52:38 Deri James wrote:
> On Sun 21 Sep 2014 06:38:42 Werner LEMBERG wrote:
>> >> A good starting point may be to implement a C/C++ library function,
>> >> to extract the MediaBox properties; that would open the gate to a
>> >> possible pdfbb request, which gtroff.exe could process internally.
>> > 
>> > 
>> > Alternatively, we could modify the existing implementation of .psbb,
>> > such that it will discriminate on `%!PS-Adobe-´ or `%PDF-´ as
>> > initial file content, then DTRT wrt parsing a `%%BoundingBox:´ or
>> > `/MediaBox´ record accordingly.
>> 
>> 
>> Good idea!
>> 
>> 
>>     Werner
> 
> Yes, it is. Someone on the list has contacted me, with a view to writing
> the code, and I have provided the perl version.
> 
> It is a bit more complex than psbb, which is essentially a grep for 
> %BoundingBox in the first part of the postscript file. This is because 
> MediaBox can appear in multiple object types in a hierarchical fashion.
> Unlike postscript, each page in a pdf document can be a different size.
> So to be sure of the correct MediaBox to use it is necessary to parse
> the complete document, find the page you are interested in (page 1 in
> the case of PDFPIC) and then search for the MediaBox in the page object
> or any of its ancestors.
> 
> Cheers 
> Deri

Just to clarify:

Strictly speaking, in PostScript also each page can be a different size
(though there is nothing built-in to groff to arrange this).

First of all, the coordinates fo placing a mark can be arbitrary.

Next, what will appear when the document is rendered will depend on
the PostScript interpreter.

The "%%BoundingBox" that Deri refers to grepping for is in fact not
part of the PostScript commands which determine what will be placed
on the page, and where; it is in fact a Comment which the PostScript
interpreter may or may not ignore. The "%%" ensure that it is ignored
when the printing instructions are carried out.

There is, for instance, a "%%PageBoundingBox:" comment defined in
the PostScript Language Specification. Quote: "This comment specifies
the bounding box that includes all the martks painted on a particular
page (this is not the bounding box of the whole document -- see the
%%BoundingBox: comment)."

So there is a lot of flexibility of this kind in PostScript; but by
default this is not exploited by groff (which, by default, does not
even insert a %%BoundingBox: comment, though one can easily do this
by putting appropriate commands in the start-up script one uses).

Best wishes to all,
Ted.

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E-Mail: (Ted Harding) <address@hidden>
Date: 21-Sep-2014  Time: 12:45:35
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