mirror of
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235 lines
7.1 KiB
Python
235 lines
7.1 KiB
Python
# coding: utf8
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# WeasyPrint converts web documents (HTML, CSS, ...) to PDF.
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# Copyright (C) 2011 Simon Sapin
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero General Public License as
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# published by the Free Software Foundation, either version 3 of the
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# License, or (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Affero General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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"""
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Specific handling for some HTML elements, especially replaced elements.
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Replaced elements (eg. <img> elements) are rendered externally and behave
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as an atomic opaque box in CSS. They may or may not have intrinsic dimensions.
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"""
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from __future__ import division
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from .formatting_structure import boxes
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from .utils import get_url_attribute
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# Maps HTML tag names to function taking an HTML element and returning a Box.
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HTML_HANDLERS = {}
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def handle_element(document, element, box):
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"""Handle HTML elements that need special care.
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:returns: a (possibly empty) list of boxes.
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"""
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if box.element_tag in HTML_HANDLERS:
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return HTML_HANDLERS[element.tag](document, element, box)
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else:
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return [box]
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def handler(tag):
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"""Return a decorator registering a function handling ``tag`` elements."""
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def decorator(function):
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"""Decorator registering a function handling ``tag`` elements."""
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HTML_HANDLERS[tag] = function
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return function
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return decorator
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def is_block_level(box):
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"""Tell wether ``box`` is supposed to be block level.
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Return ``True`` if the element is block-level, ``False`` if it is
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inline-level, and raise ValueError if it is neither.
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"""
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display = box.style.display
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if display in ('block', 'list-item', 'table'):
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return True
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elif display in ('inline', 'inline-table', 'inline-block'):
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return False
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else:
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raise ValueError('Unsupported display: ' + display)
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def make_replaced_box(element, box, replacement):
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"""Wrap a :class:`Replacement` object in either replaced box.
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That box is either block-level or inline-level, depending on what the
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element should be.
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"""
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if is_block_level(box):
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type_ = boxes.BlockLevelReplacedBox
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else:
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type_ = boxes.InlineLevelReplacedBox
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return type_(element.tag, element.sourceline, box.style, replacement)
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def make_text_box(element, box, text):
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"""Make a text box.
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If the element should be block-level, wrap it in a block box.
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"""
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text_box = boxes.TextBox(element.tag, element.sourceline,
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box.style.inherit_from(), text)
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if is_block_level(box):
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type_ = boxes.BlockBox
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else:
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type_ = boxes.InlineBox
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return type_(element.tag, element.sourceline,
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box.style, [text_box])
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@handler('img')
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def handle_img(document, element, box):
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"""Handle ``<img>`` tags, return either an image or the alt-text.
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See: http://www.w3.org/TR/html5/embedded-content-1.html#the-img-element
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"""
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src = get_url_attribute(element, 'src')
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alt = element.get('alt')
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if src:
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surface = document.get_image_surface_from_uri(src)
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if surface is not None:
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replacement = ImageReplacement(surface)
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return [make_replaced_box(element, box, replacement)]
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else:
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# Invalid image, use the alt-text.
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if alt:
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return [make_text_box(element, box, alt)]
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elif alt == '':
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# The element represents nothing
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return []
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else:
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assert alt is None
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# TODO: find some indicator that an image is missing.
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# For now, just remove the image.
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return []
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else:
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if alt:
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return [make_text_box(element, box, alt)]
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else:
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return []
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@handler('br')
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def handle_br(document, element, box):
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"""Handle ``<br>`` tags, return a preserved new-line character."""
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newline = boxes.TextBox(element.tag, element.sourceline,
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box.style, '\n')
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newline.style.white_space = 'pre'
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return [boxes.InlineBox(element.tag, element.sourceline,
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box.style, [newline])]
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def integer_attribute(element, box, name, minimum=1):
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"""Read an integer attribute from the HTML element and set it on the box.
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"""
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value = element.get(name, '').strip()
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try:
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value = int(value)
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except ValueError:
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pass
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else:
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if value >= minimum:
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setattr(box, name, value)
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@handler('colgroup')
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def handle_colgroup(document, element, box):
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"""Handle the ``span`` attribute."""
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if isinstance(box, boxes.TableColumnGroupBox):
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if any(child.tag == 'col' for child in element):
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box.span = None # sum of the children’s spans
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else:
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integer_attribute(element, box, 'span')
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return [box]
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@handler('col')
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def handle_col(document, element, box):
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"""Handle the ``span`` attribute."""
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if isinstance(box, boxes.TableColumnBox):
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integer_attribute(element, box, 'span')
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if box.span > 1:
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# Generate multiple boxes
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# http://lists.w3.org/Archives/Public/www-style/2011Nov/0293.html
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return [box.copy() for i in xrange(box.span)]
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return [box]
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@handler('th')
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@handler('td')
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def handle_td(document, element, box):
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"""Handle the ``colspan``, ``rowspan`` attributes."""
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if isinstance(box, boxes.TableCellBox):
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# HTML 4.01 gives special meaning to colspan=0
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# http://www.w3.org/TR/html401/struct/tables.html#adef-rowspan
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# but HTML 5 removed it
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# http://www.w3.org/TR/html5/tabular-data.html#attr-tdth-colspan
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# rowspan=0 is still there though.
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integer_attribute(element, box, 'colspan')
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integer_attribute(element, box, 'rowspan', minimum=0)
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return [box]
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class Replacement(object):
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"""Abstract base class for replaced elements."""
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def intrinsic_width(self):
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"""Intrinsic width if defined."""
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def intrinsic_height(self):
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"""Intrinsic height if defined."""
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def intrinsic_ratio(self):
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"""Intrinsic ratio if defined."""
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width = self.intrinsic_width()
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height = self.intrinsic_height()
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if (width is not None and height is not None and height != 0):
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return width / height
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class ImageReplacement(Replacement):
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"""Replaced ``<img>`` element.
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:param surface: a cairo :class:`ImageSurface` object.
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"""
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def __init__(self, surface):
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assert surface
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self.surface = surface
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def intrinsic_width(self):
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return self.surface.get_width()
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def intrinsic_height(self):
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return self.surface.get_height()
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def draw(self, context):
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"""Draw the element on the Cairo context."""
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context.set_source_surface(self.surface)
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context.paint()
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