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tags: allow links to page numbers not yet created

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Previously, forward references were required to use named destinations.

This patch is based on the patch in #336 by Guillaume Ayoub <guillaume.ayoub@kozea.fr>
that converted all links to indirect objects written at the end of the document.

I have reworked the patch so that only forward references to future page numbers are
written as indirect objects. Backward references and named destinations remain as they
are. This is to minimize the number of objects written to the PDF file.

Fixes #336
This commit is contained in:
Adrian Johnson 2021-07-24 21:26:22 +09:30
parent 994eccefc0
commit f7c7bcb603
4 changed files with 109 additions and 17 deletions
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93
src/cairo-pdf-interchange.c
View file

@ -335,20 +335,17 @@ cairo_pdf_interchange_write_explicit_dest (cairo_pdf_surface_t *surface,
cairo_pdf_resource_t res;
double height;
if (page < 1 || page > (int)_cairo_array_num_elements (&surface->pages))
return CAIRO_INT_STATUS_TAG_ERROR;
_cairo_array_copy_element (&surface->page_heights, page - 1, &height);
_cairo_array_copy_element (&surface->pages, page - 1, &res);
if (has_pos) {
_cairo_output_stream_printf (surface->output,
" /Dest [%d 0 R /XYZ %f %f 0]\n",
"[%d 0 R /XYZ %f %f 0]\n",
res.id,
x,
height - y);
} else {
_cairo_output_stream_printf (surface->output,
" /Dest [%d 0 R /XYZ null null 0]\n",
"[%d 0 R /XYZ null null 0]\n",
res.id);
}
@ -362,6 +359,8 @@ cairo_pdf_interchange_write_dest (cairo_pdf_surface_t *surface,
cairo_int_status_t status;
cairo_pdf_interchange_t *ic = &surface->interchange;
char *dest = NULL;
cairo_pdf_forward_link_t *link;
cairo_pdf_resource_t link_res;
if (link_attrs->dest) {
cairo_pdf_named_dest_t key;
@ -388,10 +387,11 @@ cairo_pdf_interchange_write_dest (cairo_pdf_surface_t *surface,
if (named_dest->attrs.y_valid)
y = named_dest->attrs.y;
_cairo_output_stream_printf (surface->output, " /Dest ");
status = cairo_pdf_interchange_write_explicit_dest (surface,
named_dest->page,
TRUE,
x, y);
named_dest->page,
TRUE,
x, y);
return status;
}
}
@ -406,14 +406,41 @@ cairo_pdf_interchange_write_dest (cairo_pdf_surface_t *surface,
dest);
free (dest);
} else {
status = cairo_pdf_interchange_write_explicit_dest (surface,
link_attrs->page,
link_attrs->has_pos,
link_attrs->pos.x,
link_attrs->pos.y);
if (link_attrs->page < 1)
return CAIRO_INT_STATUS_TAG_ERROR;
if (link_attrs->page <= (int)_cairo_array_num_elements (&surface->pages)) {
_cairo_output_stream_printf (surface->output, " /Dest ");
status = cairo_pdf_interchange_write_explicit_dest (surface,
link_attrs->page,
link_attrs->has_pos,
link_attrs->pos.x,
link_attrs->pos.y);
} else {
/* Link refers to a future page. Use an indirect object and
* write the link at the end of the document */
link = _cairo_malloc (sizeof (cairo_pdf_forward_link_t));
if (unlikely (link == NULL))
return _cairo_error (CAIRO_STATUS_NO_MEMORY);
link_res = _cairo_pdf_surface_new_object (surface);
if (link_res.id == 0)
return _cairo_error (CAIRO_STATUS_NO_MEMORY);
_cairo_output_stream_printf (surface->output,
" /Dest %d 0 R\n",
link_res.id);
link->res = link_res;
link->page = link_attrs->page;
link->has_pos = link_attrs->has_pos;
link->pos = link_attrs->pos;
status = _cairo_array_append (&surface->forward_links, link);
}
}
return CAIRO_STATUS_SUCCESS;
return status;
}
static cairo_int_status_t
@ -855,6 +882,36 @@ strcmp_null (const char *s1, const char *s2)
return FALSE;
}
static cairo_int_status_t
cairo_pdf_interchange_write_forward_links (cairo_pdf_surface_t *surface)
{
int num_elems, i;
cairo_pdf_forward_link_t *link;
num_elems = _cairo_array_num_elements (&surface->forward_links);
for (i = 0; i < num_elems; i++) {
link = _cairo_array_index (&surface->forward_links, i);
if (link->page > (int)_cairo_array_num_elements (&surface->pages))
return CAIRO_INT_STATUS_TAG_ERROR;
_cairo_pdf_surface_update_object (surface, link->res);
_cairo_output_stream_printf (surface->output,
"%d 0 obj\n",
link->res.id);
cairo_pdf_interchange_write_explicit_dest (surface,
link->page,
link->has_pos,
link->pos.x,
link->pos.y);
_cairo_output_stream_printf (surface->output,
"endobj\n");
}
return CAIRO_STATUS_SUCCESS;
}
static cairo_int_status_t
cairo_pdf_interchange_write_page_labels (cairo_pdf_surface_t *surface)
{
@ -1364,10 +1421,10 @@ _cairo_pdf_interchange_write_page_objects (cairo_pdf_surface_t *surface)
cairo_int_status_t status;
status = cairo_pdf_interchange_write_page_annots (surface);
if (unlikely (status))
if (unlikely (status))
return status;
cairo_pdf_interchange_clear_annotations (surface);
cairo_pdf_interchange_clear_annotations (surface);
return cairo_pdf_interchange_write_page_parent_elems (surface);
}
@ -1403,6 +1460,10 @@ _cairo_pdf_interchange_write_document_objects (cairo_pdf_surface_t *surface)
if (unlikely (status))
return status;
status = cairo_pdf_interchange_write_forward_links (surface);
if (unlikely (status))
return status;
status = cairo_pdf_interchange_write_names_dict (surface);
if (unlikely (status))
return status;

8
src/cairo-pdf-surface-private.h
View file

@ -208,6 +208,13 @@ typedef struct _cairo_pdf_outline_entry {
int count;
} cairo_pdf_outline_entry_t;
typedef struct _cairo_pdf_forward_link {
cairo_pdf_resource_t res;
int page;
cairo_bool_t has_pos;
cairo_point_double_t pos;
} cairo_pdf_forward_link_t;
struct docinfo {
char *title;
char *author;
@ -327,6 +334,7 @@ struct _cairo_pdf_surface {
cairo_pdf_interchange_t interchange;
int page_parent_tree; /* -1 if not used */
cairo_array_t page_annots;
cairo_array_t forward_links;
cairo_bool_t tagged;
char *current_page_label;
cairo_array_t page_labels;

2
src/cairo-pdf-surface.c
View file

@ -493,6 +493,7 @@ _cairo_pdf_surface_create_for_stream_internal (cairo_output_stream_t *output,
surface->page_parent_tree = -1;
_cairo_array_init (&surface->page_annots, sizeof (cairo_pdf_resource_t));
_cairo_array_init (&surface->forward_links, sizeof (cairo_pdf_forward_link_t));
surface->tagged = FALSE;
surface->current_page_label = NULL;
_cairo_array_init (&surface->page_labels, sizeof (char *));
@ -2304,6 +2305,7 @@ _cairo_pdf_surface_finish (void *abstract_surface)
_cairo_array_fini (&surface->fonts);
_cairo_array_fini (&surface->knockout_group);
_cairo_array_fini (&surface->page_annots);
_cairo_array_fini (&surface->forward_links);
if (surface->font_subsets) {
_cairo_scaled_font_subsets_destroy (surface->font_subsets);

23
test/pdf-tagged-text.c
View file

@ -318,6 +318,9 @@ draw_cover (cairo_surface_t *surface, cairo_t *cr)
const char *cairo_url = "https://www.cairographics.org/";
const double url_box_margin = 20.0;
cairo_tag_begin (cr, CAIRO_TAG_DEST, "name='cover' internal");
cairo_tag_end (cr, CAIRO_TAG_DEST);
cairo_select_font_face (cr, "Sans", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
cairo_set_font_size(cr, 16);
cairo_move_to (cr, PAGE_WIDTH/3, PAGE_HEIGHT/3);
@ -343,6 +346,12 @@ draw_cover (cairo_surface_t *surface, cairo_t *cr)
cairo_tag_begin (cr, CAIRO_TAG_LINK, buf);
cairo_tag_end (cr, CAIRO_TAG_LINK);
/* Create link to not yet emmited page number */
cairo_tag_begin (cr, CAIRO_TAG_LINK, "page=5");
cairo_move_to (cr, PAGE_WIDTH/3, 4*PAGE_HEIGHT/5);
cairo_show_text (cr, "link to page 5");
cairo_tag_end (cr, CAIRO_TAG_LINK);
draw_page_num (surface, cr, "cover", 0);
}
@ -417,6 +426,18 @@ create_document (cairo_surface_t *surface, cairo_t *cr)
sect++;
}
cairo_show_page (cr);
cairo_tag_begin (cr, CAIRO_TAG_LINK, "dest='cover'");
cairo_move_to (cr, PAGE_WIDTH/3, 2*PAGE_HEIGHT/5);
cairo_show_text (cr, "link to cover");
cairo_tag_end (cr, CAIRO_TAG_LINK);
cairo_tag_begin (cr, CAIRO_TAG_LINK, "page=3");
cairo_move_to (cr, PAGE_WIDTH/3, 3*PAGE_HEIGHT/5);
cairo_show_text (cr, "link to page 3");
cairo_tag_end (cr, CAIRO_TAG_LINK);
cairo_tag_end (cr, "Document");
}
@ -511,7 +532,7 @@ preamble (cairo_test_context_t *ctx)
cairo_destroy (cr);
cairo_surface_finish (surface);
status2 = cairo_surface_status (surface);
if (status != CAIRO_STATUS_SUCCESS)
if (status == CAIRO_STATUS_SUCCESS)
status = status2;
cairo_surface_destroy (surface);