mirror of
https://github.com/Kozea/WeasyPrint.git
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482 lines
18 KiB
Python
482 lines
18 KiB
Python
# coding: utf8
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"""
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weasyprint.layout.blocks
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------------------------
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Page breaking and layout for block-level and block-container boxes.
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:copyright: Copyright 2011-2012 Simon Sapin and contributors, see AUTHORS.
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:license: BSD, see LICENSE for details.
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"""
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from __future__ import division, unicode_literals
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from .inlines import (iter_line_boxes, replaced_box_width, replaced_box_height,
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handle_min_max_width, min_max_replaced_height,
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min_max_auto_replaced)
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from .markers import list_marker_layout
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from .tables import table_layout, fixed_table_layout, auto_table_layout
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from .percentages import resolve_percentages
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from ..formatting_structure import boxes
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from ..css.properties import Dimension
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def block_level_layout(document, box, max_position_y, skip_stack,
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containing_block, device_size, page_is_empty,
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adjoining_margins=None):
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"""Lay out the block-level ``box``.
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:param max_position_y: the absolute vertical position (as in
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``some_box.position_y``) of the bottom of the
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content box of the current page area.
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"""
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if isinstance(box, boxes.TableBox):
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return table_layout(document, box, max_position_y, skip_stack,
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containing_block, device_size, page_is_empty)
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elif isinstance(box, boxes.BlockBox):
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if box.is_table_wrapper:
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return block_table_wrapper(document, box, max_position_y,
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skip_stack, containing_block, device_size, page_is_empty,
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adjoining_margins)
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else:
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return block_box_layout(document, box, max_position_y, skip_stack,
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containing_block, device_size, page_is_empty,
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adjoining_margins)
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elif isinstance(box, boxes.BlockReplacedBox):
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box = block_replaced_box_layout(
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box, containing_block, device_size)
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resume_at = None
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next_page = 'any'
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adjoining_margins = []
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collapsing_through = False
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return box, resume_at, next_page, adjoining_margins, collapsing_through
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else: # pragma: no cover
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raise TypeError('Layout for %s not handled yet' % type(box).__name__)
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def block_box_layout(document, box, max_position_y, skip_stack,
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containing_block, device_size, page_is_empty,
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adjoining_margins=None):
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"""Lay out the block ``box``."""
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resolve_percentages(box, containing_block)
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block_level_width(box, containing_block)
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new_box, resume_at, next_page, adjoining_margins, collapsing_through = \
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block_container_layout(
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document, box, max_position_y, skip_stack,
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device_size, page_is_empty, adjoining_margins)
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list_marker_layout(document, new_box, containing_block)
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return new_box, resume_at, next_page, adjoining_margins, collapsing_through
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def block_replaced_width(box, containing_block, device_size):
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# http://www.w3.org/TR/CSS21/visudet.html#block-replaced-width
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replaced_box_width(box, device_size)
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block_level_width(box, containing_block)
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min_max_block_replaced_width = handle_min_max_width(block_replaced_width)
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def block_replaced_box_layout(box, containing_block, device_size):
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"""Lay out the block :class:`boxes.ReplacedBox` ``box``."""
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resolve_percentages(box, containing_block)
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if box.margin_top == 'auto':
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box.margin_top = 0
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if box.margin_bottom == 'auto':
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box.margin_bottom = 0
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if box.style.width == 'auto' and box.style.height == 'auto':
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block_replaced_width(box, containing_block, device_size)
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replaced_box_height(box, device_size)
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min_max_auto_replaced(box)
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else:
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min_max_block_replaced_width(box, containing_block, device_size)
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min_max_replaced_height(box, device_size)
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return box
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@handle_min_max_width
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def block_level_width(box, containing_block):
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"""Set the ``box`` width."""
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# 'cb' stands for 'containing block'
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cb_width = containing_block.width
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# http://www.w3.org/TR/CSS21/visudet.html#blockwidth
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# These names are waaay too long
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margin_l = box.margin_left
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margin_r = box.margin_right
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padding_l = box.padding_left
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padding_r = box.padding_right
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border_l = box.border_left_width
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border_r = box.border_right_width
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width = box.width
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# Only margin-left, margin-right and width can be 'auto'.
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# We want: width of containing block ==
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# margin-left + border-left-width + padding-left + width
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# + padding-right + border-right-width + margin-right
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paddings_plus_borders = padding_l + padding_r + border_l + border_r
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if box.width != 'auto':
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total = paddings_plus_borders + width
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if margin_l != 'auto':
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total += margin_l
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if margin_r != 'auto':
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total += margin_r
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if total > cb_width:
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if margin_l == 'auto':
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margin_l = box.margin_left = 0
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if margin_r == 'auto':
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margin_r = box.margin_right = 0
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if width != 'auto' and margin_l != 'auto' and margin_r != 'auto':
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# The equation is over-constrained
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margin_sum = cb_width - paddings_plus_borders - width
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if containing_block.style.direction == 'ltr':
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margin_r = box.margin_right = margin_sum - margin_l
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else:
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margin_l = box.margin_left = margin_sum - margin_r
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if width == 'auto':
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if margin_l == 'auto':
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margin_l = box.margin_left = 0
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if margin_r == 'auto':
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margin_r = box.margin_right = 0
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width = box.width = cb_width - (
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paddings_plus_borders + margin_l + margin_r)
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margin_sum = cb_width - paddings_plus_borders - width
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if margin_l == 'auto' and margin_r == 'auto':
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box.margin_left = margin_sum / 2.
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box.margin_right = margin_sum / 2.
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elif margin_l == 'auto' and margin_r != 'auto':
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box.margin_left = margin_sum - margin_r
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elif margin_l != 'auto' and margin_r == 'auto':
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box.margin_right = margin_sum - margin_l
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def block_container_layout(document, box, max_position_y, skip_stack,
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device_size, page_is_empty, adjoining_margins=None):
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"""Set the ``box`` height."""
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assert isinstance(box, boxes.BlockContainerBox)
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# TODO: this should make a difference, but that is currently neglected.
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# See http://www.w3.org/TR/CSS21/visudet.html#normal-block
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# http://www.w3.org/TR/CSS21/visudet.html#root-height
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#if box.style.overflow != 'visible':
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# ...
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if box.margin_top == 'auto':
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box.margin_top = 0
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if box.margin_bottom == 'auto':
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box.margin_bottom = 0
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if adjoining_margins is None:
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adjoining_margins = []
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adjoining_margins.append(box.margin_top)
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this_box_adjoining_margins = adjoining_margins
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collapsing_with_children = not (box.border_top_width or box.padding_top
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or establishes_formatting_context(box) or box.is_for_root_element)
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if collapsing_with_children:
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# XXX not counting margins in adjoining_margins, if any
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position_y = box.position_y
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else:
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box.position_y += collapse_margin(adjoining_margins) - box.margin_top
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adjoining_margins = []
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position_y = box.content_box_y()
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position_x = box.content_box_x()
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new_children = []
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next_page = 'any'
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if skip_stack is None:
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skip = 0
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else:
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skip, skip_stack = skip_stack
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for index, child in box.enumerate_skip(skip):
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if not child.is_in_normal_flow():
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continue
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child.position_x = position_x
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# XXX does not count margins in adjoining_margins:
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child.position_y = position_y
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if isinstance(child, boxes.LineBox):
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assert len(box.children) == 1, (
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'line box with siblings before layout')
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if adjoining_margins:
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position_y += collapse_margin(adjoining_margins)
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adjoining_margins = []
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new_containing_block = box
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lines_iterator = iter_line_boxes(
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document, child, position_y, skip_stack,
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new_containing_block, device_size)
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new_lines = []
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is_page_break = False
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for line, resume_at in lines_iterator:
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new_position_y = position_y + line.height
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# Allow overflow if the first line of the page is higher
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# than the page itself so that we put *something* on this
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# page and can advance in the document.
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if new_position_y > max_position_y and (
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new_lines or not page_is_empty):
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over_orphans = len(new_lines) - box.style.orphans
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if over_orphans < 0 and not page_is_empty:
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# Reached the bottom of the page before we had
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# enough lines for orphans, cancel the whole box.
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return None, None, 'any', [], False
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# How many lines we need on the next page to satisfy widows
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# -1 for the current line.
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needed = box.style.widows - 1
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if needed:
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for _ in lines_iterator:
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needed -= 1
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if needed == 0:
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break
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if needed > over_orphans and not page_is_empty:
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# Total number of lines < orphans + widows
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return None, None, 'any', [], False
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if needed and needed <= over_orphans:
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# Remove lines to keep them for the next page
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del new_lines[-needed:]
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# Page break here, resume before this line
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resume_at = (index, skip_stack)
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is_page_break = True
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break
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new_lines.append((line, resume_at))
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position_y = new_position_y
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skip_stack = resume_at
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new_children = [line for line, resume_at in new_lines]
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if new_lines:
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_, resume_at = new_lines[-1]
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resume_at = (index, resume_at)
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if is_page_break:
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break
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else:
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if new_children:
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# between siblings, but not before the first child
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# or after the last child.
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break_here, next_page = forced_page_break(
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new_children[-1], child)
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if break_here:
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resume_at = (index, None)
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break
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new_containing_block = box
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(new_child, resume_at, next_page, next_adjoining_margins,
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collapsing_through) = block_level_layout(
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document, child, max_position_y, skip_stack,
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new_containing_block, device_size,
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page_is_empty and not new_children,
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adjoining_margins)
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skip_stack = None
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if new_child is not None:
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# We need to do this after the child layout to have the
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# used value for margin_top (eg. it might be a percentage.)
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if not isinstance(new_child, boxes.BlockBox):
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adjoining_margins.append(new_child.margin_top)
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offset_y = (collapse_margin(adjoining_margins)
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- new_child.margin_top)
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new_child.translate(0, offset_y)
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adjoining_margins = []
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#else: blocks handle that themselves.
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adjoining_margins = next_adjoining_margins
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adjoining_margins.append(new_child.margin_bottom)
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if not collapsing_through:
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new_position_y = (
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new_child.border_box_y() + new_child.border_height())
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if (new_position_y > max_position_y and (
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new_children or not page_is_empty)
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and not isinstance(child, boxes.BlockBox)):
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# The child overflows the page area, put it on the
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# next page. (But don’t delay whole blocks if eg.
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# only the bottom border overflows.)
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new_child = None
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else:
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position_y = new_position_y
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if new_child is None:
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if new_children:
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resume_at = (index, None)
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break
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else:
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# This was the first child of this box, cancel the box
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# completly
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return None, None, 'any', [], False
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# Bottom borders may overflow here
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# TODO: back-track somehow when all lines fit but not borders
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new_children.append(new_child)
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if resume_at is not None:
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resume_at = (index, resume_at)
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break
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else:
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resume_at = None
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if resume_at is not None and box.style.page_break_inside == 'avoid' \
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and not page_is_empty:
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return None, None, 'any', [], False
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if collapsing_with_children:
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if new_children and not isinstance(
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# margins are used for something else on line boxes
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new_children[0], boxes.LineBox):
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border_box_y = new_children[0].border_box_y()
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else:
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# this_adjoining_margins contains box.margin_top
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border_box_y = box.position_y + collapse_margin(
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this_box_adjoining_margins)
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box.position_y = border_box_y - box.margin_top
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collapsing_through = False
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if new_children:
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# bottom margin of the last child and bottom margin of this box ...
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if box.height != 'auto':
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# not adjoining. (position_y is not used afterwards.)
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adjoining_margins = []
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else:
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# top and bottom margin of this box
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if box.height in ('auto', 0) and box.min_height == 0:
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collapsing_through = True
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else:
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# not adjoining. (position_y is not used afterwards.)
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adjoining_margins = []
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if box.border_bottom_width or box.padding_bottom or (
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establishes_formatting_context(box) or box.is_for_root_element):
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position_y += collapse_margin(adjoining_margins)
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adjoining_margins = []
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new_box = box.copy_with_children(new_children)
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# TODO: See corner cases in
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# http://www.w3.org/TR/CSS21/visudet.html#normal-block
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if new_box.height == 'auto':
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new_box.height = position_y - new_box.content_box_y()
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new_box.height = max(
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min(new_box.height, new_box.max_height),
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new_box.min_height)
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if resume_at is not None:
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# If there was a list marker, we kept it on `new_box`.
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# Do not repeat it on `box` on the next page.
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# TODO: Do this non-destructively
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box.outside_list_marker = None
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box.reset_spacing('top')
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new_box.reset_spacing('bottom')
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return new_box, resume_at, next_page, adjoining_margins, collapsing_through
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def block_table_wrapper(document, wrapper, max_position_y, skip_stack,
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containing_block, device_size, page_is_empty,
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adjoining_margins):
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"""Layout for the wrapper of a block-level table wrapper."""
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for child in wrapper.children:
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if isinstance(child, boxes.TableBox):
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table = child
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break
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else: # pragma: no cover
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raise ValueError('Table wrapper without a table')
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resolve_percentages(wrapper, containing_block)
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resolve_percentages(table, containing_block)
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# Count the wrapper margins in case of `width: auto`
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table.margin_left = wrapper.margin_left
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table.margin_right = wrapper.margin_right
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if table.style.table_layout == 'fixed':
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block_level_width(table, containing_block)
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fixed_table_layout(table)
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else:
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auto_table_layout(table, wrapper, containing_block)
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# The table margins are on the table wrapper box, not on the table box
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table.margin_left = 0
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table.margin_right = 0
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wrapper.width = table.border_width()
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wrapper.style.width = Dimension(wrapper.width, 'px')
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return block_box_layout(document, wrapper, max_position_y, skip_stack,
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containing_block, device_size, page_is_empty,
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adjoining_margins)
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def collapse_margin(adjoining_margins):
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"""Return the amount of collapsed margin for a list of adjoining margins.
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"""
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# Add 0 to make sure that neither max() or min() get an empty list
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margins = [0]
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margins.extend(adjoining_margins)
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positives = (m for m in margins if m >= 0)
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negatives = (m for m in margins if m <= 0)
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return max(positives) + min(negatives)
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def establishes_formatting_context(box):
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"""Return wether a box establishes a block formatting context.
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See http://www.w3.org/TR/CSS2/visuren.html#block-formatting
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"""
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return box.is_floated() or box.is_absolutely_positioned() or (
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isinstance(box, boxes.BlockContainerBox)
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and not isinstance(box, boxes.BlockBox)
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) or (
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isinstance(box, boxes.BlockBox) and box.style.overflow != 'visible'
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)
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def forced_page_break(sibling_before, sibling_after):
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"""Return the value of ``page-break-before`` or ``page-break-after``
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that "wins" for boxes that meet at the margin between two sibling boxes.
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For boxes before the margin, the 'page-break-after' value is considered;
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for boxes after the margin the 'page-break-before' value is considered.
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Return (break_here, next_page) where break_here is a boolean, and
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next_page the side the next page should be on: 'left', 'right', or 'any'
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"""
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counts = dict(
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avoid=False,
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auto=False,
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left=False,
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right=False,
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always=False,
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)
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for box, index, property_name in [
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(sibling_before, -1, 'page_break_after'),
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(sibling_after, 0, 'page_break_before')]:
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while 1:
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counts[box.style[property_name]] = True
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if not getattr(box, 'children', None):
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break
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box = box.children[index]
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if not isinstance(box, boxes.BlockLevelBox):
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break
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left = counts['left']
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right = counts['right']
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if left and right:
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# Nonsense. Just do a single page break
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return True, 'any'
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if left:
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return True, 'left'
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if right:
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return True, 'right'
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if counts['always']:
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return True, 'any'
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return False, 'any'
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# TODO: support 'avoid'
|