PrintOperation.addOnDrawPage

Emitted for every page that is printed. The signal handler must render the page_nr's page onto the cairo context obtained from context using PrintContext.getCairoContext.

static void
draw_page (GtkPrintOperation *operation,
GtkPrintContext   *context,
gint               page_nr,
gpointer           user_data)
{
cairo_t *cr;
PangoLayout *layout;
gdouble width, text_height;
gint layout_height;
PangoFontDescription *desc;

cr = gtk_print_context_get_cairo_context (context);
width = gtk_print_context_get_width (context);

cairo_rectangle (cr, 0, 0, width, HEADER_HEIGHT);

cairo_set_source_rgb (cr, 0.8, 0.8, 0.8);
cairo_fill (cr);

layout = gtk_print_context_create_pango_layout (context);

desc = pango_font_description_from_string ("sans 14");
pango_layout_set_font_description (layout, desc);
pango_font_description_free (desc);

pango_layout_set_text (layout, "some text", -1);
pango_layout_set_width (layout, width * PANGO_SCALE);
pango_layout_set_alignment (layout, PANGO_ALIGN_CENTER);

pango_layout_get_size (layout, NULL, &layout_height);
text_height = (gdouble)layout_height / PANGO_SCALE;

cairo_move_to (cr, width / 2,  (HEADER_HEIGHT - text_height) / 2);
pango_cairo_show_layout (cr, layout);

g_object_unref (layout);
}

Use PrintOperation.setUseFullPage and PrintOperation.setUnit before starting the print operation to set up the transformation of the cairo context according to your needs.