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weave: use emplacement method, scrap TOC repair

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The new emplacement method updates page objects in place without
generating new objgen numbers, meaning we no longer need to update the table
of contents to preserve links.
This commit is contained in:
James R. Barlow
2019-05-11 12:40:25 -07:00
parent 83398e54ea
commit 15a988b999
2 changed files with 14 additions and 134 deletions
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src/ocrmypdf/_weave.py
+14 -114
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@@ -189,99 +189,6 @@ def _find_font(text, pdf_base):
return None, None
def _traverse_toc(pdf_base, visitor_fn, log):
"""
Walk the table of contents, calling visitor_fn() at each node
The /Outlines data structure is a messy data structure, but rather than
navigating hierarchically we just track unique nodes. Enqueue nodes when
we find them, and never visit them again. set() is awesome. We look for
the two types of object in the table of contents that can be page bookmarks
and update the page entry.
"""
visited = set()
queue = set()
link_keys = ('/Parent', '/First', '/Last', '/Prev', '/Next')
if not '/Outlines' in pdf_base.root:
return
queue.add(pdf_base.root.Outlines.objgen)
while queue:
objgen = queue.pop()
visited.add(objgen)
node = pdf_base.get_object(objgen)
log.debug('fix toc: exploring outline entries at %r', objgen)
# Enumerate other nodes we could visit from here
for key in link_keys:
if key not in node:
continue
item = node[key]
if not item.is_indirect:
# Direct references are not allowed here, but it's not clear
# what we should do if we find any. Removing them is an option:
# node[key] = pdf_base.make_indirect(None)
continue
objgen = item.objgen
if objgen not in visited:
queue.add(objgen)
if visitor_fn:
visitor_fn(pdf_base, node, log)
def _fix_toc(pdf_base, pageref_remap, log):
"""Repair the table of contents
Whenever we replace a page wholesale, it gets assigned a new objgen number
and other references to it within the PDF become invalid, most notably in
the table of contents (/Outlines in PDF-speak). In weave_layers we collect
pageref_remap, a mapping that describes the new objgen number given an old
one. (objgen is a tuple, and the gen is almost always zero.)
It may ultimately be better to find a way to rebuild a page in place.
"""
if not pageref_remap:
return
def remap_dest(dest_node):
"""
Inner helper function: change the objgen for any page from the old we
invalidated to its new one.
"""
try:
pageref = dest_node[0]
if pageref['/Type'] == '/Page' and pageref.objgen in pageref_remap:
new_objgen = pageref_remap[pageref.objgen]
dest_node[0] = pdf_base.get_object(new_objgen)
except (IndexError, TypeError) as e:
log.warning("This file may contain invalid table of contents entries")
log.debug(e)
def visit_remap_dest(pdf_base, node, log):
"""
Visitor function to fix ToC entries
Test for the two types of references to pages that can occur in ToCs.
Both types have the same final format (an indirect reference to the
target page).
"""
if '/Dest' in node:
# /Dest reference to another page (old method)
remap_dest(node['/Dest'])
elif '/A' in node:
# /A (action) command set to "GoTo" (newer method)
if '/S' in node['/A'] and node['/A']['/S'] == '/GoTo':
remap_dest(node['/A']['/D'])
_traverse_toc(pdf_base, visit_remap_dest, log)
def weave_layers(infiles, output_file, log, context):
"""Apply text layer and/or image layer changes to baseline file
@@ -324,13 +231,12 @@ def weave_layers(infiles, output_file, log, context):
pdf_base = pikepdf.open(path_base)
font, font_key, procset = None, None, None
pdfinfo = context.get_pdfinfo()
pagerefs = {}
procset = pdf_base.make_indirect(
pikepdf.Object.parse(b'[ /PDF /Text /ImageB /ImageC /ImageI ]')
)
replacements = 1
emplacements = 1
interim_count = 0
# Iterate rest
@@ -345,30 +251,25 @@ def weave_layers(infiles, output_file, log, context):
if text and not font:
font, font_key = _find_font(text, pdf_base)
replacing = False
emplaced_page = False
content_rotation = pdfinfo[page_num - 1].rotation
path_image = Path(image).resolve() if image else None
if path_image is not None and path_image != path_base:
# We are replacing the old page with a rasterized PDF of the new
# page
log.debug("Replace")
old_objgen = pdf_base.pages[page_num - 1].objgen
# We are updating the old page with a rasterized PDF of the new
# page (without changing objgen, to preserve references)
log.debug("Emplacement update")
with pikepdf.open(image) as pdf_image:
replacements += 1
image_page = pdf_image.pages[0]
pdf_base.pages[page_num - 1] = image_page
# We're adding a new page, which will get a new objgen number pair,
# so we need to update any references to it. qpdf did not like
# my attempt to update the old object in place, but that is an
# option to consider
pagerefs[old_objgen] = pdf_base.pages[page_num - 1].objgen
replacing = True
emplacements += 1
foreign_image_page = pdf_image.pages[0]
pdf_base.pages.append(foreign_image_page)
local_image_page = pdf_base.pages[-1]
pdf_base.pages[page_num - 1].emplace(local_image_page)
del pdf_base.pages[-1]
emplaced_page = True
autorotate_correction = context.get_rotation(page_num - 1)
if replacing:
if emplaced_page:
content_rotation = autorotate_correction
text_rotation = autorotate_correction
text_misaligned = (text_rotation - content_rotation) % 360
@@ -397,7 +298,7 @@ def weave_layers(infiles, output_file, log, context):
content_rotation - autorotate_correction
) % 360
if replacements % MAX_REPLACE_PAGES == 0:
if emplacements % MAX_REPLACE_PAGES == 0:
# Periodically save and reload the Pdf object. This will keep a
# lid on our memory usage for very large files. Attach the font to
# page 1 even if page 1 doesn't use it, so we have a way to get it
@@ -427,6 +328,5 @@ def weave_layers(infiles, output_file, log, context):
font, font_key = None, None # Ensure we reacquire this information
interim_count += 1
_fix_toc(pdf_base, pagerefs, log)
pdf_base.save(output_file)
pdf_base.close()