[cairo] pdf hyperlinks

John Ellson ellson at research.att.com
Wed Feb 18 07:31:50 PST 2009

Why is this PDF specific?

We also need facilities for inserting anchors into SVG.


Adrian Johnson wrote:
> Dan McMahill wrote:
>> Hello,
>> Quite some time back there was a proposal on this list for an API for 
>> supporting hyperlinks in the pdf output from cairo.  Has there been any 
>> further discussion or movement towards implementing this?
> At the last cairo summit it was agreed that the best way to make the 
> non-graphical PDF features available would be to provide a minimal API 
> for inserting objects into the PDF and offload the work to an external 
> library [1].
> I've recently started looking into this. I've started work on a patch 
> for allowing objects to be inserted into the PDF [2]. This allows some 
> of the PDF features such as outlines and annotations to be implemented. 
> Additional API would be required to support the full set of PDF features.
> Currently the API is:
> Allocate an object number for later use by cairo_pdf_surface_insert_object()
>    int
>    cairo_pdf_surface_allocate_object (cairo_surface_t *surface)
> Insert a dictionary and stream into the PDF file. stream may be NULL if 
> only a dictionary is required.
>    void
>    cairo_pdf_surface_insert_object (cairo_surface_t      *surface,
>                                     int                   object,
>                                     const char           *dictionary,
>                                     cairo_pdf_read_func_t stream,
>                                     void                 *closure)
> Insert a key/value pair into the dictionary specified by type
>    typedef enum _cairo_pdf_dictionary_type {
>    } cairo_pdf_dictionary_type_t;
>    void
>    cairo_pdf_surface_insert_dictionary_entry (cairo_surface_t *surface,
>                                      cairo_pdf_dictionary_type_t type,
>                                      const char               *key,
>                                      const char               *value)
> Return the object number of the current page. I intend changing this to 
> take a page number so the object number of any page can be obtained.
>    int
>    cairo_pdf_surface_get_page_object (cairo_surface_t *surface)
> I've also started coding a library that makes the additional PDF 
> features available to cairo using the above API [3]. I've used the 
> placeholder name "cpdf" for the library until someone can suggest a 
> better name.
> At present there is not much there. Just a bit of code for creating 
> outlines, a function for setting the PDF metadata, and an attempt at 
> getting link annotations to work. At this stage I've only been writing 
> this code to help design and test the cairo API for inserting PDF 
> objects. A real library for adding advanced PDF features to cairo PDFs 
> may look very different to this.
> [1] http://www.cairographics.org/summit/2008/notes/
> [2] http://cgit.freedesktop.org/~ajohnson/cairo/log/?h=pdf-insert-object
> [3] http://cgit.freedesktop.org/~ajohnson/cpdf/
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