[cairo] How to reuse an image source surface on the PDF backend

[Rafael Viotti]

Hello list,

  first of all thanks for this awesome library that is Cairo!

  I'm working on the PDF file generation module of a CRM web
application. I have been using Cairo for that with great success.
Everything was going well.

  Now I have to draw a background image on each page of the PDF
document. A problem arose. Those tiny PDF files are now huge because
Cairo is repeating the image stream for each page shown.

  Here's a code snippet that illustrates how the PDF module of the
application works:

#include <cairo-pdf.h>

#define DPI 96.0
#define PX_2_PT(x) (x * (72.0 / DPI))
#define PDF_W PX_2_PT(645.0)
#define PDF_H PX_2_PT(560.0)

int main (int argc, char *argv[]) {
    cairo_surface_t *img, *pdf;
    cairo_t *ctx;

    img = cairo_image_surface_create_from_png("bg.png");
    pdf = cairo_pdf_surface_create("out.pdf", PDF_W, PDF_H);
    ctx = cairo_create(pdf);

    cairo_scale(ctx, PX_2_PT(1.0), PX_2_PT(1.0));

    cairo_set_source_surface(ctx, img, 0.0, 0.0);

    cairo_paint(ctx);
    cairo_show_page(ctx);

    cairo_paint(ctx);
    cairo_show_page(ctx);

    cairo_paint(ctx);
    cairo_show_page(ctx);

    cairo_paint(ctx);
    cairo_show_page(ctx);

    cairo_paint(ctx);
    cairo_show_page(ctx);

    cairo_surface_finish(pdf);

    cairo_destroy(ctx);
    cairo_surface_destroy(img);
    cairo_surface_destroy(pdf);

    return 0;
}

  This program generates a PDF file approximately five times bigger
than the source RGB image.

  I'm testing with Cairo 1.9.2 snapshot. I've seen from the Cairo docs
that cairo_set_source_surface creates a pattern for the surface and
from the conversation below that Cairo 1.9.2 (and the 1.10 release) do
support pattern reuse.

http://lists.cairographics.org/archives/cairo/2009-September/018084.html

  So, is it possible to generate only one image stream on the PDF
file? If so, how can it be done?

Cheers from Brazil,
Rafael.