[cairo] Clickable links in PDF? Metadata?

[Andreas Lobinger]

Hello colleague,

i'm not fully aware of the cairo development and do not have insight
into roadmap or feature planning, so the following might need
correction.

Cairo is clearly targeted at rendering - quality and consitently over
all output media - not at document management. The features your are
asking for are part of the pdf document structure and metadata and i'd
not expect this to be handled by Cairo. I have some background in
processing and creating pdf - i wrote once SW to change something in
the pdf structure - like updating the MediaBox, collecting pages from
1-page document into 1 document etc. and from that time i'd recommend
(for your use case) to look for another library to support the
document structure. pdflib lite e.g. comes to my mind. The pdf rending
model is quite straight forward (exc. color managment), the major part
in a pdf document is the document structure.

Wishing a happy day,
        Andreas

On Fri, Jul 3, 2015 at 6:37 PM, David Kastrup <dak at gnu.org> wrote:
>
> Hi,
>
> I'm currently taking a look at the suitability of using Cairo for the
> rendering purposes of GNU LilyPond <URL:http://www.lilypond.org>.
> Hardly surprising, print output is pretty much a priority.
>
> There are a few loose ends for which I see nothing in the
> documentation.  With regard to PDF production, I cannot find the
> following two items:
>
> a) clickable links
> b) document metadata
> c) interfacing with the PDF production
>
> While one can write out (sub-)surfaces via a streaming interface, it is
> not clear whether one can assemble a single PDF file from multiple
> surfaces such that resources are only present once, and how one would
> otherwise organize the PDF output such that user-defined elements can be
> spliced in.  If c) was reasonably available and powerful, the other
> points could be implemented as user-defined extensions.
>
> Even if it seems like overkill to render every item with a clickable
> link in a surface of its own.
>
> There is also stuff like "attaching files" to a PDF (not as important).
> It may be that this works with the MIME data extensions already.
>
> Any further information about this stuff?  Present state, plans,
> problems, possible interfaces/APIs, timelines, openness to third-party
> contributions?
>
> Oh, it also seems like surface types are hardcoded.  It might make sense
> to let the user define a surface of his/her own by providing hooks for
> _everything_.  For a vector-based format like PDF, this might be
> reasonably straightforward and consequently a somewhat doable way of
> getting a surface able to do everything that is required for a
> particular application.
>
> Thanks for any pointers/thoughts!
>
> --
> David Kastrup
>
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