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Ambulance Clerc
306
venv/Lib/site-packages/weasyprint/layout/column.py
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306
venv/Lib/site-packages/weasyprint/layout/column.py
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"""
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weasyprint.layout.columns
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-------------------------
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Layout for columns.
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"""
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from math import floor
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from .absolute import absolute_layout
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from .percent import resolve_percentages
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def columns_layout(context, box, bottom_space, skip_stack, containing_block,
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page_is_empty, absolute_boxes, fixed_boxes,
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adjoining_margins):
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"""Lay out a multi-column ``box``."""
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from .block import (
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block_box_layout, block_level_layout, block_level_width,
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collapse_margin)
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# Implementation of the multi-column pseudo-algorithm:
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# https://www.w3.org/TR/css3-multicol/#pseudo-algorithm
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width = None
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style = box.style
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original_bottom_space = bottom_space
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if box.style['position'] == 'relative':
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# New containing block, use a new absolute list
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absolute_boxes = []
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box = box.copy_with_children(box.children)
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box.position_y += collapse_margin(adjoining_margins) - box.margin_top
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height = box.style['height']
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if height != 'auto' and height.unit != '%':
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assert height.unit == 'px'
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known_height = True
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bottom_space = max(
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bottom_space,
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context.page_bottom - box.content_box_y() - height.value)
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else:
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known_height = False
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# TODO: the available width can be unknown if the containing block needs
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# the size of this block to know its own size.
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block_level_width(box, containing_block)
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available_width = box.width
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if style['column_width'] == 'auto' and style['column_count'] != 'auto':
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count = style['column_count']
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width = max(
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0, available_width - (count - 1) * style['column_gap']) / count
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elif (style['column_width'] != 'auto' and
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style['column_count'] == 'auto'):
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count = max(1, int(floor(
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(available_width + style['column_gap']) /
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(style['column_width'] + style['column_gap']))))
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width = (
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(available_width + style['column_gap']) / count -
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style['column_gap'])
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else:
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count = min(style['column_count'], int(floor(
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(available_width + style['column_gap']) /
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(style['column_width'] + style['column_gap']))))
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width = (
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(available_width + style['column_gap']) / count -
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style['column_gap'])
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def create_column_box(children):
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column_box = box.anonymous_from(box, children=children)
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resolve_percentages(column_box, containing_block)
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column_box.is_column = True
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column_box.width = width
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column_box.position_x = box.content_box_x()
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column_box.position_y = box.content_box_y()
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return column_box
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# Handle column-span property.
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# We want to get the following structure:
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# columns_and_blocks = [
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# [column_child_1, column_child_2],
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# spanning_block,
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# …
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# ]
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columns_and_blocks = []
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column_children = []
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for child in box.children:
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if child.style['column_span'] == 'all':
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if column_children:
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columns_and_blocks.append(column_children)
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columns_and_blocks.append(child.copy())
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column_children = []
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continue
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column_children.append(child.copy())
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if column_children:
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columns_and_blocks.append(column_children)
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if not box.children:
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next_page = {'break': 'any', 'page': None}
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skip_stack = None
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# Balance.
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#
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# The current algorithm starts from the ideal height (the total height
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# divided by the number of columns). We then iterate until the last column
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# is not the highest one. At the end of each loop, we add the minimal
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# height needed to make one direct child at the top of one column go to the
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# end of the previous column.
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#
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# We rely on a real rendering for each loop, and with a stupid algorithm
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# like this it can last minutes…
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adjoining_margins = []
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current_position_y = box.content_box_y()
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new_children = []
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for column_children_or_block in columns_and_blocks:
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if not isinstance(column_children_or_block, list):
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# We get a spanning block, we display it like other blocks.
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block = column_children_or_block
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resolve_percentages(block, containing_block)
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block.position_x = box.content_box_x()
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block.position_y = current_position_y
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new_child, _, _, adjoining_margins, _ = block_level_layout(
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context, block, original_bottom_space, skip_stack,
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containing_block, page_is_empty, absolute_boxes, fixed_boxes,
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adjoining_margins, discard=False)
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new_children.append(new_child)
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current_position_y = (
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new_child.border_height() + new_child.border_box_y())
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adjoining_margins.append(new_child.margin_bottom)
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continue
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excluded_shapes = context.excluded_shapes[:]
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# We have a list of children that we have to balance between columns.
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column_children = column_children_or_block
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# Find the total height of the content
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current_position_y += collapse_margin(adjoining_margins)
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adjoining_margins = []
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column_box = create_column_box(column_children)
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column_box.position_y = current_position_y
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new_child, _, _, _, _ = block_box_layout(
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context, column_box, -float('inf'), skip_stack, containing_block,
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page_is_empty, [], [], [], discard=False)
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height = new_child.margin_height()
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if style['column_fill'] == 'balance':
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height /= count
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# Try to render columns until the content fits, increase the column
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# height step by step.
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column_skip_stack = skip_stack
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lost_space = float('inf')
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while True:
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# Remove extra excluded shapes introduced during previous loop
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new_excluded_shapes = (
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len(context.excluded_shapes) - len(excluded_shapes))
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for i in range(new_excluded_shapes):
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context.excluded_shapes.pop()
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for i in range(count):
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# Render the column
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new_box, resume_at, next_page, _, _ = block_box_layout(
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context, column_box,
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context.page_bottom - current_position_y - height,
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column_skip_stack, containing_block, page_is_empty,
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[], [], [], discard=False)
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if new_box is None:
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# We didn't render anything. Give up and use the max
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# content height.
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height *= count
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continue
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column_skip_stack = resume_at
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in_flow_children = [
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child for child in new_box.children
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if child.is_in_normal_flow()]
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if in_flow_children:
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# Get the empty space at the bottom of the column box
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empty_space = height - (
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in_flow_children[-1].position_y - box.content_box_y() +
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in_flow_children[-1].margin_height())
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# Get the minimum size needed to render the next box
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next_box, _, _, _, _ = block_box_layout(
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context, column_box,
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context.page_bottom - box.content_box_y(),
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column_skip_stack, containing_block, True, [], [], [],
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discard=False)
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for child in next_box.children:
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if child.is_in_normal_flow():
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next_box_size = child.margin_height()
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break
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else:
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empty_space = next_box_size = 0
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# Append the size needed to render the next box in this
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# column.
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#
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# The next box size may be smaller than the empty space, for
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# example when the next box can't be separated from its own
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# next box. In this case we don't try to find the real value
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# and let the workaround below fix this for us.
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#
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# We also want to avoid very small values that may have been
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# introduced by rounding errors. As the workaround below at
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# least adds 1 pixel for each loop, we can ignore lost spaces
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# lower than 1px.
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if next_box_size - empty_space > 1:
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lost_space = min(lost_space, next_box_size - empty_space)
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# Stop if we already rendered the whole content
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if resume_at is None:
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break
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if column_skip_stack is None:
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# We rendered the whole content, stop
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break
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else:
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if lost_space == float('inf'):
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# We didn't find the extra size needed to render a child in
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# the previous column, increase height by the minimal
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# value.
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height += 1
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else:
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# Increase the columns heights and render them once again
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height += lost_space
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column_skip_stack = skip_stack
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# TODO: check box.style['max']-height
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bottom_space = max(
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bottom_space, context.page_bottom - current_position_y - height)
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# Replace the current box children with columns
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i = 0
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max_column_height = 0
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columns = []
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while True:
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if i == count - 1:
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bottom_space = original_bottom_space
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column_box = create_column_box(column_children)
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column_box.position_y = current_position_y
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if style['direction'] == 'rtl':
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column_box.position_x += (
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box.width - (i + 1) * width - i * style['column_gap'])
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else:
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column_box.position_x += i * (width + style['column_gap'])
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new_child, column_skip_stack, column_next_page, _, _ = (
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block_box_layout(
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context, column_box, bottom_space, skip_stack,
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containing_block, page_is_empty, absolute_boxes,
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fixed_boxes, None, discard=False))
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if new_child is None:
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break
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next_page = column_next_page
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skip_stack = column_skip_stack
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columns.append(new_child)
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max_column_height = max(
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max_column_height, new_child.margin_height())
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if skip_stack is None:
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break
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i += 1
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if i == count and not known_height:
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# [If] a declaration that constrains the column height
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# (e.g., using height or max-height). In this case,
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# additional column boxes are created in the inline
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# direction.
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break
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current_position_y += max_column_height
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for column in columns:
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column.height = max_column_height
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new_children.append(column)
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if box.children and not new_children:
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# The box has children but none can be drawn, let's skip the whole box
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return None, (0, None), {'break': 'any', 'page': None}, [], False
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# Set the height of box and the columns
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box.children = new_children
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current_position_y += collapse_margin(adjoining_margins)
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height = current_position_y - box.content_box_y()
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if box.height == 'auto':
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box.height = height
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height_difference = 0
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else:
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height_difference = box.height - height
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if box.min_height != 'auto' and box.min_height > box.height:
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height_difference += box.min_height - box.height
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box.height = box.min_height
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for child in new_children[::-1]:
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if child.is_column:
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child.height += height_difference
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else:
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break
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if box.style['position'] == 'relative':
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# New containing block, resolve the layout of the absolute descendants
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for absolute_box in absolute_boxes:
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absolute_layout(
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context, absolute_box, box, fixed_boxes, bottom_space,
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skip_stack=None)
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return box, skip_stack, next_page, [], False
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