mirror of
https://github.com/Kozea/WeasyPrint.git
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549 lines
17 KiB
Python
549 lines
17 KiB
Python
# coding: utf8
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"""
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weasyprint.css.computed_values
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------------------------------
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Convert *specified* property values (the result of the cascade and
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inhertance) into *computed* values (that are inherited).
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:copyright: Copyright 2011-2014 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 .properties import INITIAL_VALUES, Dimension
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from ..urls import get_link_attribute
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from .. import text
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ZERO_PIXELS = Dimension(0, 'px')
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# How many CSS pixels is one <unit>?
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# http://www.w3.org/TR/CSS21/syndata.html#length-units
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LENGTHS_TO_PIXELS = {
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'px': 1,
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'pt': 1. / 0.75,
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'pc': 16., # LENGTHS_TO_PIXELS['pt'] * 12
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'in': 96., # LENGTHS_TO_PIXELS['pt'] * 72
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'cm': 96. / 2.54, # LENGTHS_TO_PIXELS['in'] / 2.54
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'mm': 96. / 25.4, # LENGTHS_TO_PIXELS['in'] / 25.4
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}
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# Value in pixels of font-size for <absolute-size> keywords: 12pt (16px) for
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# medium, and scaling factors given in CSS3 for others:
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# http://www.w3.org/TR/css3-fonts/#font-size-prop
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# TODO: this will need to be ordered to implement 'smaller' and 'larger'
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FONT_SIZE_KEYWORDS = dict(
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# medium is 16px, others are a ratio of medium
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(name, INITIAL_VALUES['font_size'] * a / b)
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for name, a, b in [
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('xx-small', 3, 5),
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('x-small', 3, 4),
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('small', 8, 9),
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('medium', 1, 1),
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('large', 6, 5),
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('x-large', 3, 2),
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('xx-large', 2, 1),
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]
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)
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# These are unspecified, other than 'thin' <='medium' <= 'thick'.
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# Values are in pixels.
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BORDER_WIDTH_KEYWORDS = {
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'thin': 1,
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'medium': 3,
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'thick': 5,
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}
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assert INITIAL_VALUES['border_top_width'] == BORDER_WIDTH_KEYWORDS['medium']
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# http://www.w3.org/TR/CSS21/fonts.html#propdef-font-weight
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FONT_WEIGHT_RELATIVE = dict(
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bolder={
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100: 400,
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200: 400,
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300: 400,
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400: 700,
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500: 700,
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600: 900,
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700: 900,
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800: 900,
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900: 900,
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},
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lighter={
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100: 100,
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200: 100,
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300: 100,
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400: 100,
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500: 100,
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600: 400,
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700: 400,
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800: 700,
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900: 700,
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},
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)
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# http://www.w3.org/TR/css3-page/#size
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# name=(width in pixels, height in pixels)
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PAGE_SIZES = dict(
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a5=(
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Dimension(148, 'mm'),
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Dimension(210, 'mm'),
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),
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a4=(
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Dimension(210, 'mm'),
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Dimension(297, 'mm'),
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),
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a3=(
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Dimension(297, 'mm'),
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Dimension(420, 'mm'),
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),
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b5=(
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Dimension(176, 'mm'),
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Dimension(250, 'mm'),
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),
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b4=(
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Dimension(250, 'mm'),
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Dimension(353, 'mm'),
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),
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letter=(
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Dimension(8.5, 'in'),
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Dimension(11, 'in'),
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),
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legal=(
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Dimension(8.5, 'in'),
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Dimension(14, 'in'),
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),
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ledger=(
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Dimension(11, 'in'),
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Dimension(17, 'in'),
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),
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)
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# In "portrait" orientation.
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for w, h in PAGE_SIZES.values():
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assert w.value < h.value
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INITIAL_PAGE_SIZE = PAGE_SIZES['a4']
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INITIAL_VALUES['size'] = tuple(
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d.value * LENGTHS_TO_PIXELS[d.unit] for d in INITIAL_PAGE_SIZE)
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def _computing_order():
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"""Some computed values are required by others, so order matters."""
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first = [
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'font_stretch', 'font_weight', 'font_family', 'font_variant',
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'font_style', 'font_size', 'line_height']
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order = sorted(INITIAL_VALUES)
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for name in first:
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order.remove(name)
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return tuple(first + order)
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COMPUTING_ORDER = _computing_order()
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# Maps property names to functions returning the computed values
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COMPUTER_FUNCTIONS = {}
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def register_computer(name):
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"""Decorator registering a property ``name`` for a function."""
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name = name.replace('-', '_')
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def decorator(function):
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"""Register the property ``name`` for ``function``."""
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COMPUTER_FUNCTIONS[name] = function
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return function
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return decorator
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def compute(element, pseudo_type, specified, computed, parent_style):
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"""
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Return a StyleDict of computed values.
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:param element: The HTML element these style apply to
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:param pseudo_type: The type of pseudo-element, eg 'before', None
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:param specified: a :class:`StyleDict` of specified values. Should contain
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values for all properties.
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:param computed: a :class:`StyleDict` of already known computed values.
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Only contains some properties (or none).
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:param parent_values: a :class:`StyleDict` of computed values of the parent
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element (should contain values for all properties),
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or ``None`` if ``element`` is the root element.
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"""
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if parent_style is None:
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parent_style = INITIAL_VALUES
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computer = lambda: 0 # Dummy object that holds attributes
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computer.element = element
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computer.pseudo_type = pseudo_type
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computer.specified = specified
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computer.computed = computed
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computer.parent_style = parent_style
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getter = COMPUTER_FUNCTIONS.get
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for name in COMPUTING_ORDER:
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if name in computed:
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# Already computed
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continue
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value = specified[name]
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function = getter(name)
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if function is not None:
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value = function(computer, name, value)
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# else: same as specified
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computed[name] = value
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computed['_weasy_specified_display'] = specified.display
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return computed
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# Let's be consistent, always use ``name`` as an argument even when
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# it is useless.
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# pylint: disable=W0613
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@register_computer('background-image')
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def background_image(computer, name, values):
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"""Compute lenghts in gradient background-image."""
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for type_, value in values:
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if type_ in ('linear-gradient', 'radial-gradient'):
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value.stop_positions = [
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length(computer, name, pos) if pos is not None else None
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for pos in value.stop_positions]
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if type_ == 'radial-gradient':
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value.center, = background_position(computer, name, [value.center])
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if value.size_type == 'explicit':
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value.size = length_or_percentage_tuple(
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computer, name, value.size)
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return values
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@register_computer('background-position')
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def background_position(computer, name, values):
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"""Compute lengths in background-position."""
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return [
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(origin_x, length(computer, name, pos_x),
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origin_y, length(computer, name, pos_y))
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for origin_x, pos_x, origin_y, pos_y in values]
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@register_computer('transform-origin')
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def length_or_percentage_tuple(computer, name, values):
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"""Compute the lists of lengths that can be percentages."""
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return tuple(length(computer, name, value) for value in values)
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@register_computer('border-spacing')
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@register_computer('size')
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@register_computer('clip')
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def length_tuple(computer, name, values):
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"""Compute the properties with a list of lengths."""
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return tuple(length(computer, name, value, pixels_only=True)
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for value in values)
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@register_computer('top')
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@register_computer('right')
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@register_computer('left')
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@register_computer('bottom')
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@register_computer('margin-top')
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@register_computer('margin-right')
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@register_computer('margin-bottom')
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@register_computer('margin-left')
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@register_computer('height')
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@register_computer('width')
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@register_computer('min-width')
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@register_computer('min-height')
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@register_computer('max-width')
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@register_computer('max-height')
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@register_computer('padding-top')
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@register_computer('padding-right')
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@register_computer('padding-bottom')
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@register_computer('padding-left')
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@register_computer('text-indent')
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@register_computer('hyphenate-limit-zone')
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def length(computer, name, value, font_size=None, pixels_only=False):
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"""Compute a length ``value``."""
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if value == 'auto':
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return value
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if value.value == 0:
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return 0 if pixels_only else ZERO_PIXELS
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unit = value.unit
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if unit == 'px':
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return value.value if pixels_only else value
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elif unit in LENGTHS_TO_PIXELS:
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# Convert absolute lengths to pixels
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result = value.value * LENGTHS_TO_PIXELS[unit]
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elif unit in ('em', 'ex', 'ch'):
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if font_size is None:
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font_size = computer.computed.font_size
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if unit == 'ex':
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# TODO: cache
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result = value.value * font_size * ex_ratio(computer.computed)
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elif unit == 'ch':
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# TODO: cache
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layout = text.Layout(
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hinting=False, font_size=font_size,
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style=computer.computed)
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layout.set_text('0')
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line, = layout.iter_lines()
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logical_width, _ = text.get_size(line)
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result = value.value * logical_width
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elif unit == 'em':
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result = value.value * font_size
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else:
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# A percentage or 'auto': no conversion needed.
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return value
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return result if pixels_only else Dimension(result, 'px')
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@register_computer('letter-spacing')
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def pixel_length(computer, name, value):
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if value == 'normal':
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return value
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else:
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return length(computer, name, value, pixels_only=True)
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@register_computer('background-size')
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def background_size(computer, name, values):
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"""Compute the ``background-size`` properties."""
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return [value if value in ('contain', 'cover') else
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length_or_percentage_tuple(computer, name, value)
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for value in values]
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@register_computer('border-top-width')
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@register_computer('border-right-width')
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@register_computer('border-left-width')
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@register_computer('border-bottom-width')
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@register_computer('outline-width')
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def border_width(computer, name, value):
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"""Compute the ``border-*-width`` properties."""
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style = computer.computed[name.replace('width', 'style')]
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if style in ('none', 'hidden'):
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return 0
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if value in BORDER_WIDTH_KEYWORDS:
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return BORDER_WIDTH_KEYWORDS[value]
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if isinstance(value, int):
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# The initial value can get here, but length() would fail as
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# it does not have a 'unit' attribute.
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return value
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return length(computer, name, value, pixels_only=True)
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@register_computer('border-top-left-radius')
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@register_computer('border-top-right-radius')
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@register_computer('border-bottom-left-radius')
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@register_computer('border-bottom-right-radius')
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def border_radius(computer, name, values):
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"""Compute the ``border-*-radius`` properties."""
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return [length(computer, name, value) for value in values]
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@register_computer('content')
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def content(computer, name, values):
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"""Compute the ``content`` property."""
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if values in ('normal', 'none'):
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return values
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else:
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return [('STRING', computer.element.get(value, ''))
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if type_ == 'attr' else (type_, value)
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for type_, value in values]
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@register_computer('display')
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def display(computer, name, value):
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"""Compute the ``display`` property.
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See http://www.w3.org/TR/CSS21/visuren.html#dis-pos-flo
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"""
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float_ = computer.specified.float
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position = computer.specified.position
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if position in ('absolute', 'fixed') or float_ != 'none' or \
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getattr(computer.element, 'getparent', lambda: None)() is None:
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if value == 'inline-table':
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return'table'
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elif value in ('inline', 'table-row-group', 'table-column',
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'table-column-group', 'table-header-group',
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'table-footer-group', 'table-row', 'table-cell',
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'table-caption', 'inline-block'):
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return 'block'
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return value
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@register_computer('float')
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def compute_float(computer, name, value):
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"""Compute the ``float`` property.
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See http://www.w3.org/TR/CSS21/visuren.html#dis-pos-flo
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"""
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if computer.specified.position in ('absolute', 'fixed'):
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return 'none'
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else:
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return value
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@register_computer('font-size')
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def font_size(computer, name, value):
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"""Compute the ``font-size`` property."""
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if value in FONT_SIZE_KEYWORDS:
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return FONT_SIZE_KEYWORDS[value]
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# TODO: support 'larger' and 'smaller'
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parent_font_size = computer.parent_style['font_size']
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if value.unit == '%':
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return value.value * parent_font_size / 100.
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else:
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return length(computer, name, value, pixels_only=True,
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font_size=parent_font_size)
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@register_computer('font-weight')
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def font_weight(computer, name, value):
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"""Compute the ``font-weight`` property."""
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if value == 'normal':
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return 400
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elif value == 'bold':
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return 700
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elif value in ('bolder', 'lighter'):
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parent_value = computer.parent_style['font_weight']
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# Use a string here as StyleDict.__setattr__ turns integers into pixel
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# lengths. This is a number without unit.
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return FONT_WEIGHT_RELATIVE[value][parent_value]
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else:
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return value
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@register_computer('line-height')
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def line_height(computer, name, value):
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"""Compute the ``line-height`` property."""
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if value == 'normal':
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return value
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elif not value.unit:
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return ('NUMBER', value.value)
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elif value.unit == '%':
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factor = value.value / 100.
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font_size_value = computer.computed.font_size
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pixels = factor * font_size_value
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else:
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pixels = length(computer, name, value, pixels_only=True)
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return ('PIXELS', pixels)
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@register_computer('anchor')
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def anchor(computer, name, values):
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"""Compute the ``anchor`` property."""
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if values != 'none':
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_, key = values
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return computer.element.get(key) or None
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@register_computer('link')
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def link(computer, name, values):
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"""Compute the ``link`` property."""
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if values == 'none':
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return None
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else:
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type_, value = values
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if type_ == 'attr':
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return get_link_attribute(computer.element, value)
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else:
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return values
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@register_computer('lang')
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def lang(computer, name, values):
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"""Compute the ``lang`` property."""
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if values == 'none':
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return None
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else:
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type_, key = values
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if type_ == 'attr':
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return computer.element.get(key) or None
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elif type_ == 'string':
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return key
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@register_computer('transform')
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def transform(computer, name, value):
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"""Compute the ``transform`` property."""
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result = []
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for function, args in value:
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if function == 'translate':
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args = length_or_percentage_tuple(computer, name, args)
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result.append((function, args))
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return result
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@register_computer('vertical-align')
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def vertical_align(computer, name, value):
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"""Compute the ``vertical-align`` property."""
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# Use +/- half an em for super and sub, same as Pango.
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# (See the SUPERSUB_RISE constant in pango-markup.c)
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if value in ('baseline', 'middle', 'text-top', 'text-bottom',
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'top', 'bottom'):
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return value
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elif value == 'super':
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return computer.computed.font_size * 0.5
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elif value == 'sub':
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return computer.computed.font_size * -0.5
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elif value.unit == '%':
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height, _ = strut_layout(computer.computed)
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return height * value.value / 100.
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else:
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return length(computer, name, value, pixels_only=True)
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@register_computer('word-spacing')
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def word_spacing(computer, name, value):
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"""Compute the ``word-spacing`` property."""
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if value == 'normal':
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return 0
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else:
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return length(computer, name, value, pixels_only=True)
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def strut_layout(style, hinting=True):
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"""Return a tuple of the used value of ``line-height`` and the baseline.
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The baseline is given from the top edge of line height.
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"""
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# TODO: cache these results for a given set of styles?
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line_height = style.line_height
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if style.font_size == 0:
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pango_height = baseline = 0
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else:
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# TODO: get the real value for `hinting`? (if we really care…)
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_, _, _, _, pango_height, baseline = text.split_first_line(
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'', style, hinting=hinting, max_width=None, line_width=None)
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if line_height == 'normal':
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return pango_height, baseline
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type_, value = line_height
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if type_ == 'NUMBER':
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value *= style.font_size
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return value, baseline + (value - pango_height) / 2
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def ex_ratio(style):
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"""Return the ratio 1ex/font_size, according to given style."""
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font_size = 1000 # big value
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layout = text.Layout(hinting=False, font_size=font_size, style=style)
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layout.set_text('x')
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line, = layout.iter_lines()
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_, ink_height_above_baseline = text.get_ink_position(line)
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# Zero means some kind of failure, fallback is 0.5.
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# We round to try keeping exact values that were altered by Pango.
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return round(-ink_height_above_baseline / font_size, 5) or 0.5
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