python-pdfrw 0+svn136-3 / usr / share / pyshared / pdfrw / buildxobj.py

# A part of pdfrw (pdfrw.googlecode.com)
# Copyright (C) 2006-2009 Patrick Maupin, Austin, Texas
# MIT license -- See LICENSE.txt for details

'''

This module contains code to build PDF "Form XObjects".

A Form XObject allows a fragment from one PDF file to be cleanly
included in another PDF file.

Reference for syntax: "Parameters for opening PDF files" from SDK 8.1

        http://www.adobe.com/devnet/acrobat/pdfs/pdf_open_parameters.pdf

        supported 'page=xxx', 'viewrect=<left>,<top>,<width>,<height>'

        Units are in points

Reference for content:   Adobe PDF reference, sixth edition, version 1.7

        http://www.adobe.com/devnet/acrobat/pdfs/pdf_reference_1-7.pdf

        Form xobjects discussed chapter 4.9, page 355
'''

from pdfobjects import PdfDict, PdfArray, PdfName
from pdfreader import PdfReader

class ViewInfo(object):
    ''' Instantiate ViewInfo with a uri, and it will parse out
        the filename, page, and viewrect into object attributes.
    '''
    doc = None
    docname = None
    page = None
    viewrect = None

    def __init__(self, pageinfo='', **kw):
        pageinfo=pageinfo.split('#',1)
        if len(pageinfo) == 2:
            pageinfo[1:] = pageinfo[1].replace('&', '#').split('#')
        for key in 'page viewrect'.split():
            if pageinfo[0].startswith(key+'='):
                break
        else:
            self.docname = pageinfo.pop(0)
        for item in pageinfo:
            key, value = item.split('=')
            key = key.strip()
            value = value.replace(',', ' ').split()
            if key == 'page':
                assert len(value) == 1
                setattr(self, key, int(value[0]))
            elif key == 'viewrect':
                assert len(value) == 4
                setattr(self, key, [float(x) for x in value])
            else:
                log.error('Unknown option: %s', key)
        for key, value in kw.iteritems():
            assert hasattr(self, key), key
            setattr(self, key, value)

def getrects(inheritable, pageinfo):
    ''' Given the inheritable attributes of a page and
        the desired pageinfo rectangle, return the page's
        media box and the calculated boundary (clip) box.
    '''
    mbox = tuple([float(x) for x in inheritable.MediaBox])
    vrect = pageinfo.viewrect
    if vrect is None:
        cbox = tuple([float(x) for x in (inheritable.CropBox or mbox)])
    else:
        mleft, mbot, mright, mtop = mbox
        x, y, w, h = vrect
        cleft = mleft + x
        ctop = mtop - y
        cright = cleft + w
        cbot = ctop - h
        cbox = max(mleft, cleft), max(mbot, cbot), min(mright, cright), min(mtop, ctop)
    return mbox, cbox

def _cache_xobj(contents, resources, mbox, bbox):
    ''' Return a cached Form XObject, or create a new one and cache it.
    '''
    cachedict = contents.xobj_cachedict
    if cachedict is None:
        cachedict = contents.private.xobj_cachedict = {}
    result = cachedict.get(bbox)
    if result is None:
        func = (_get_fullpage, _get_subpage)[mbox != bbox]
        result = PdfDict(
            func(contents, resources, mbox, bbox),
            Type = PdfName.XObject,
            Subtype = PdfName.Form,
            FormType = 1,
            BBox = PdfArray(bbox),
        )
        cachedict[bbox] = result
    return result

def _get_fullpage(contents, resources, mbox, bbox):
    ''' fullpage is easy.  Just copy the contents,
        set up the resources, and let _cache_xobj handle the
        rest.
    '''
    return PdfDict(contents, Resources=resources)

def _get_subpage(contents, resources, mbox, bbox):
    ''' subpages *could* be as easy as full pages, but we
        choose to complicate life by creating a Form XObject
        for the page, and then one that references it for
        the subpage, on the off-chance that we want multiple
        items from the page.
    '''
    return PdfDict(
        stream = '/FullPage Do\n',
        Resources = PdfDict(
            XObject = PdfDict(
                FullPage = _cache_xobj(contents, resources, mbox, mbox)
            )
        )
    )

def pagexobj(page, viewinfo=ViewInfo(), allow_compressed=True):
    ''' pagexobj creates and returns a Form XObject for
        a given view within a page (Defaults to entire page.)
    '''
    inheritable = page.inheritable
    resources = inheritable.Resources
    mbox, bbox = getrects(inheritable, viewinfo)
    contents = page.Contents
    # Make sure the only attribute is length
    # All the filters must have been executed
    assert int(contents.Length) == len(contents.stream)
    if not allow_compressed:
        assert len([x for x in contents.iteritems()]) == 1

    return _cache_xobj(contents, resources, mbox, bbox)


def docxobj(pageinfo, doc=None, allow_compressed=True):
    ''' docxobj creates and returns an actual Form XObject.
        Can work standalone, or in conjunction with
        the CacheXObj class (below).
    '''
    if not isinstance(pageinfo, ViewInfo):
        pageinfo = ViewInfo(pageinfo)

    # If we're explicitly passed a document,
    # make sure we don't have one implicitly as well.
    # If no implicit or explicit doc, then read one in
    # from the filename.
    if doc is not None:
        assert pageinfo.doc is None
        pageinfo.doc = doc
    elif pageinfo.doc is not None:
        doc = pageinfo.doc
    else:
        doc = pageinfo.doc = PdfReader(pageinfo.docname, decompress = not allow_compressed)
    assert isinstance(doc, PdfReader)

    sourcepage = doc.pages[(pageinfo.page or 1) - 1]
    return pagexobj(sourcepage, pageinfo, allow_compressed)


class CacheXObj(object):
    ''' Use to keep from reparsing files over and over,
        and to keep from making the output too much
        bigger than it ought to be by replicating
        unnecessary object copies.
    '''
    def __init__(self, decompress=False):
        ''' Set decompress true if you need
            the Form XObjects to be decompressed.
            Will decompress what it can and scream
            about the rest.
        '''
        self.cached_pdfs = {}
        self.decompress = decompress

    def load(self, sourcename):
        ''' Load a Form XObject from a uri
        '''
        info = ViewInfo(sourcename)
        fname = info.docname
        pcache = self.cached_pdfs
        doc = pcache.get(fname)
        if doc is None:
            doc = pcache[fname] = PdfReader(fname, decompress=self.decompress)
        return docxobj(info, doc, allow_compressed=not self.decompress)