draw.py

# coding: utf8
"""
    weasyprint.draw
    ---------------

    Take an "after layout" box tree and draw it onto a cairo context.

    :copyright: Copyright 2011-2014 Simon Sapin and contributors, see AUTHORS.
    :license: BSD, see LICENSE for details.

"""

from __future__ import division, unicode_literals

import contextlib
import math
import operator

import cairocffi as cairo

from .formatting_structure import boxes
from .stacking import StackingContext
from .text import show_first_line
from .compat import xrange


SIDES = ('top', 'right', 'bottom', 'left')


@contextlib.contextmanager
def stacked(context):
    """Save and restore the context when used with the ``with`` keyword."""
    context.save()
    try:
        yield
    finally:
        context.restore()


def hsv2rgb(hue, saturation, value):
    """Transform a HSV color to a RGB color."""
    c = value * saturation
    x = c * (1 - abs((hue / 60) % 2 - 1))
    m = value - c
    if 0 <= hue < 60:
        return c + m, x + m, m
    elif 60 <= hue < 120:
        return x + m, c + m, m
    elif 120 <= hue < 180:
        return m, c + m, x + m
    elif 180 <= hue < 240:
        return m, x + m, c + m
    elif 240 <= hue < 300:
        return x + m, m, c + m
    elif 300 <= hue < 360:
        return c + m, m, x + m


def rgb2hsv(red, green, blue):
    """Transform a RGB color to a HSV color."""
    cmax = max(red, green, blue)
    cmin = min(red, green, blue)
    delta = cmax - cmin
    if delta == 0:
        hue = 0
    elif cmax == red:
        hue = 60 * ((green - blue) / delta % 6)
    elif cmax == green:
        hue = 60 * ((blue - red) / delta + 2)
    elif cmax == blue:
        hue = 60 * ((red - green) / delta + 4)
    saturation = 0 if delta == 0 else delta / cmax
    return hue, saturation, cmax


def darken(color):
    """Return a darker color."""
    hue, saturation, value = rgb2hsv(color.red, color.green, color.blue)
    value /= 1.5
    saturation /= 1.25
    return hsv2rgb(hue, saturation, value) + (color.alpha,)


def lighten(color):
    """Return a lighter color."""
    hue, saturation, value = rgb2hsv(color.red, color.green, color.blue)
    value = 1 - (1 - value) / 1.5
    if saturation:
        saturation = 1 - (1 - saturation) / 1.25
    return hsv2rgb(hue, saturation, value) + (color.alpha,)


def draw_page(page, context, enable_hinting):
    """Draw the given PageBox."""
    stacking_context = StackingContext.from_page(page)
    draw_background(
        context, stacking_context.box.background, enable_hinting,
        clip_box=False)
    draw_background(
        context, page.canvas_background, enable_hinting, clip_box=False)
    draw_border(context, page, enable_hinting)
    draw_stacking_context(context, stacking_context, enable_hinting)


def draw_box_background_and_border(context, page, box, enable_hinting):
    draw_background(context, box.background, enable_hinting)
    if isinstance(box, boxes.TableBox):
        for column_group in box.column_groups:
            draw_box_background_and_border(
                context, page, column_group, enable_hinting)
        for row_group in box.children:
            draw_background(context, row_group.background, enable_hinting)
            for row in row_group.children:
                draw_background(context, row.background, enable_hinting)
                for cell in row.children:
                    draw_background(context, cell.background, enable_hinting)
        if box.style.border_collapse == 'separate':
            draw_border(context, box, enable_hinting)
            for row_group in box.children:
                for row in row_group.children:
                    for cell in row.children:
                        draw_border(context, cell, enable_hinting)
        else:
            draw_collapsed_borders(context, box, enable_hinting)
    elif isinstance(box, (boxes.TableColumnGroupBox, boxes.TableRowGroupBox)):
        for child in box.children:
            draw_box_background_and_border(
                context, page, child, enable_hinting)
    else:
        draw_border(context, box, enable_hinting)


def draw_stacking_context(context, stacking_context, enable_hinting):
    """Draw a ``stacking_context`` on ``context``."""
    # See http://www.w3.org/TR/CSS2/zindex.html
    with stacked(context):
        box = stacking_context.box
        if box.is_absolutely_positioned() and box.style.clip:
            top, right, bottom, left = box.style.clip
            if top == 'auto':
                top = 0
            if right == 'auto':
                right = 0
            if bottom == 'auto':
                bottom = box.border_height()
            if left == 'auto':
                left = box.border_width()
            context.rectangle(
                box.border_box_x() + right,
                box.border_box_y() + top,
                left - right,
                bottom - top)
            context.clip()

        if box.style.opacity < 1:
            context.push_group()

        if box.transformation_matrix:
            context.transform(box.transformation_matrix)

        # Point 1 is done in draw_page

        # Point 2
        if isinstance(box, (boxes.BlockBox, boxes.MarginBox,
                            boxes.InlineBlockBox, boxes.TableCellBox)):
            # The canvas background was removed by set_canvas_background
            draw_box_background_and_border(
                context, stacking_context.page, box, enable_hinting)

        with stacked(context):
            if box.style.overflow != 'visible':
                # Only clip the content and the children:
                # - the background is already clipped
                # - the border must *not* be clipped
                rounded_box_path(context, box.rounded_padding_box())
                context.clip()

            # Point 3
            for child_context in stacking_context.negative_z_contexts:
                draw_stacking_context(context, child_context, enable_hinting)

            # Point 4
            for block in stacking_context.block_level_boxes:
                draw_box_background_and_border(
                    context, stacking_context.page, block, enable_hinting)

            # Point 5
            for child_context in stacking_context.float_contexts:
                draw_stacking_context(context, child_context, enable_hinting)

            # Point 6
            if isinstance(box, boxes.InlineBox):
                draw_inline_level(
                    context, stacking_context.page, box, enable_hinting)

            # Point 7
            for block in [box] + stacking_context.blocks_and_cells:
                marker_box = getattr(block, 'outside_list_marker', None)
                if marker_box:
                    draw_inline_level(
                        context, stacking_context.page, marker_box,
                        enable_hinting)

                if isinstance(block, boxes.ReplacedBox):
                    draw_replacedbox(context, block)
                else:
                    for child in block.children:
                        if isinstance(child, boxes.LineBox):
                            # TODO: draw inline tables
                            draw_inline_level(
                                context, stacking_context.page, child,
                                enable_hinting)

            # Point 8
            for child_context in stacking_context.zero_z_contexts:
                draw_stacking_context(context, child_context, enable_hinting)

            # Point 9
            for child_context in stacking_context.positive_z_contexts:
                draw_stacking_context(context, child_context, enable_hinting)

        # Point 10
        draw_outlines(context, box, enable_hinting)

        if box.style.opacity < 1:
            context.pop_group_to_source()
            context.paint_with_alpha(box.style.opacity)


def rounded_box_path(context, radii):
    """Draw the path of the border radius box.

    ``widths`` is a tuple of the inner widths (top, right, bottom, left) from
    the border box. Radii are adjusted from these values. Default is (0, 0, 0,
    0).

    Inspired by Cairo Cookbook
    http://cairographics.org/cookbook/roundedrectangles/

    """
    x, y, w, h, tl, tr, br, bl = radii

    if 0 in tl:
        tl = (0, 0)
    if 0 in tr:
        tr = (0, 0)
    if 0 in br:
        br = (0, 0)
    if 0 in bl:
        bl = (0, 0)

    if (tl, tr, br, bl) == 4 * ((0, 0),):
        # No radius, draw a rectangle
        context.rectangle(x, y, w, h)
        return

    context.move_to(x, y)
    for i, (w, h, (rx, ry)) in enumerate((
            (0, 0, tl), (w, 0, tr), (w, h, br), (0, h, bl))):
        context.save()
        context.translate(x + w, y + h)
        radius = max(rx, ry)
        if radius:
            context.scale(min(rx / ry, 1), min(ry / rx, 1))
        context.arc(
            (-1 if w else 1) * radius, (-1 if h else 1) * radius, radius,
            (2 + i) * math.pi / 2, (3 + i) * math.pi / 2)
        context.restore()


def draw_background(context, bg, enable_hinting, clip_box=True):
    """Draw the background color and image to a ``cairo.Context``.

    If ``clip_box`` is set to ``False``, the background is not clipped to the
    border box of the background, but only to the painting area.

    """
    if bg is None:
        return

    with stacked(context):
        if enable_hinting:
            # Prefer crisp edges on background rectangles.
            context.set_antialias(cairo.ANTIALIAS_NONE)

        if clip_box:
            rounded_box_path(context, bg.layers[-1].rounded_box)
            context.clip()

        # Background color
        if bg.color.alpha > 0:
            with stacked(context):
                painting_area = bg.layers[-1].painting_area
                if painting_area:
                    context.rectangle(*painting_area)
                    context.clip()
                context.set_source_rgba(*bg.color)
                context.paint()

        # Paint in reversed order: first layer is "closest" to the viewer.
        for layer in reversed(bg.layers):
            draw_background_image(context, layer, bg.image_rendering)


def draw_background_image(context, layer, image_rendering):
    # Background image
    if layer.image is None:
        return

    painting_x, painting_y, painting_width, painting_height = (
        layer.painting_area)
    positioning_x, positioning_y, positioning_width, positioning_height = (
        layer.positioning_area)
    position_x, position_y = layer.position
    repeat_x, repeat_y = layer.repeat
    image_width, image_height = layer.size

    if repeat_x == 'no-repeat':
        repeat_width = painting_width * 2
    elif repeat_x in ('repeat', 'round'):
        repeat_width = image_width
    else:
        assert repeat_x == 'space'
        n_repeats = math.floor(positioning_width / image_width)
        if n_repeats >= 2:
            repeat_width = (positioning_width - image_width) / (n_repeats - 1)
            position_x = 0  # Ignore background-position for this dimension
        else:
            repeat_width = image_width

    if repeat_y == 'no-repeat':
        repeat_height = painting_height * 2
    elif repeat_y in ('repeat', 'round'):
        repeat_height = image_height
    else:
        assert repeat_y == 'space'
        n_repeats = math.floor(positioning_height / image_height)
        if n_repeats >= 2:
            repeat_height = (
                positioning_height - image_height) / (n_repeats - 1)
            position_y = 0  # Ignore background-position for this dimension
        else:
            repeat_height = image_height

    sub_surface = cairo.PDFSurface(None, repeat_width, repeat_height)
    sub_context = cairo.Context(sub_surface)
    sub_context.rectangle(0, 0, image_width, image_height)
    sub_context.clip()
    layer.image.draw(sub_context, image_width, image_height, image_rendering)
    pattern = cairo.SurfacePattern(sub_surface)
    pattern.set_extend(cairo.EXTEND_REPEAT)

    with stacked(context):
        if not layer.unbounded:
            context.rectangle(painting_x, painting_y,
                              painting_width, painting_height)
            context.clip()
        # else: unrestricted, whole page box

        context.translate(positioning_x + position_x,
                          positioning_y + position_y)
        context.set_source(pattern)
        context.paint()


def xy_offset(x, y, offset_x, offset_y, offset):
    """Increment X and Y coordinates by the given offsets."""
    return x + offset_x * offset, y + offset_y * offset


def styled_color(style, color, side):
    if style in ('inset', 'outset'):
        do_lighten = (side in ('top', 'left')) ^ (style == 'inset')
        return (lighten if do_lighten else darken)(color)
    elif style in ('ridge', 'groove'):
        if (side in ('top', 'left')) ^ (style == 'ridge'):
            return lighten(color), darken(color)
        else:
            return darken(color), lighten(color)
    return color


def draw_border(context, box, enable_hinting):
    """Draw the box border to a ``cairo.Context``."""
    # We need a plan to draw beautiful borders, and that's difficult, no need
    # to lie. Let's try to find the cases that we can handle in a smart way.

    # The box is hidden, easy.
    if box.style.visibility != 'visible':
        return

    widths = [getattr(box, 'border_%s_width' % side) for side in SIDES]

    # No border, return early.
    if all(width == 0 for width in widths):
        return

    colors = [box.style.get_color('border_%s_color' % side) for side in SIDES]
    styles = [
        colors[i].alpha and box.style['border_%s_style' % side]
        for (i, side) in enumerate(SIDES)]

    # The 4 sides are solid or double, and they have the same color. Oh yeah!
    # We can draw them so easily!
    if set(styles) in (set(('solid',)), set(('double',))) and (
            len(set(colors)) == 1):
        draw_rounded_border(context, box, styles[0], colors[0])
        return

    # We're not smart enough to find a good way to draw the borders :/. We must
    # draw them side by side.
    for side, width, color, style in zip(SIDES, widths, colors, styles):
        if width == 0 or not color:
            continue
        with stacked(context):
            clip_border_segment(
                context, enable_hinting, style, width, side,
                box.rounded_border_box()[:4], widths,
                box.rounded_border_box()[4:])
            draw_rounded_border(
                context, box, style, styled_color(style, color, side))


def clip_border_segment(context, enable_hinting, style, width, side,
                        border_box, border_widths=None, radii=None):
    """Clip one segment of box border.

    The strategy is to remove the zones not needed because of the style or the
    side before painting.

    """
    if enable_hinting and style != 'dotted' and (
            # Borders smaller than 1 device unit would disappear
            # without anti-aliasing.
            math.hypot(*context.user_to_device(width, 0)) >= 1 and
            math.hypot(*context.user_to_device(0, width)) >= 1):
        # Avoid an artifact in the corner joining two solid borders
        # of the same color.
        context.set_antialias(cairo.ANTIALIAS_NONE)

    bbx, bby, bbw, bbh = border_box
    (tlh, tlv), (trh, trv), (brh, brv), (blh, blv) = radii or 4 * ((0, 0),)
    bt, br, bb, bl = border_widths or 4 * (width,)

    def transition_point(x1, y1, x2, y2):
        """Get the point use for border transition.

        The extra boolean returned is ``True`` if the point is in the padding
        box (ie. the padding box is rounded).

        This point is not specified. We must be sure to be inside the rounded
        padding box, and in the zone defined in the "transition zone" allowed
        by the specification. We chose the corner of the transition zone. It's
        easy to get and gives quite good results, but it seems to be different
        from what other browsers do.

        """
        return (
            ((x1, y1), True) if abs(x1) > abs(x2) and abs(y1) > abs(y2)
            else ((x2, y2), False))

    def corner_half_length(a, b):
        """Return the length of the half of one ellipsis corner.

        Inspired by [Ramanujan, S., "Modular Equations and Approximations to
        pi" Quart. J. Pure. Appl. Math., vol. 45 (1913-1914), pp. 350-372],
        wonderfully explained by Dr Rob.

        http://mathforum.org/dr.math/faq/formulas/

        """
        x = (a - b) / (a + b)
        return math.pi / 8 * (a + b) * (
            1 + 3 * x ** 2 / (10 + math.sqrt(4 - 3 * x ** 2)))

    if side == 'top':
        (px1, py1), rounded1 = transition_point(tlh, tlv, bl, bt)
        (px2, py2), rounded2 = transition_point(-trh, trv, -br, bt)
        width = bt
        way = 1
        angle = 1
        main_offset = bby
    elif side == 'right':
        (px1, py1), rounded1 = transition_point(-trh, trv, -br, bt)
        (px2, py2), rounded2 = transition_point(-brh, -brv, -br, -bb)
        width = br
        way = 1
        angle = 2
        main_offset = bbx + bbw
    elif side == 'bottom':
        (px1, py1), rounded1 = transition_point(blh, -blv, bl, -bb)
        (px2, py2), rounded2 = transition_point(-brh, -brv, -br, -bb)
        width = bb
        way = -1
        angle = 3
        main_offset = bby + bbh
    elif side == 'left':
        (px1, py1), rounded1 = transition_point(tlh, tlv, bl, bt)
        (px2, py2), rounded2 = transition_point(blh, -blv, bl, -bb)
        width = bl
        way = -1
        angle = 4
        main_offset = bbx

    if side in ('top', 'bottom'):
        a1, b1 = px1 - bl / 2, way * py1 - width / 2
        a2, b2 = -px2 - br / 2, way * py2 - width / 2
        line_length = bbw - px1 + px2
        length = bbw
        context.move_to(bbx + bbw, main_offset)
        context.rel_line_to(-bbw, 0)
        context.rel_line_to(px1, py1)
        context.rel_line_to(-px1 + bbw + px2, -py1 + py2)
    elif side in ('left', 'right'):
        a1, b1 = -way * px1 - width / 2, py1 - bt / 2
        a2, b2 = -way * px2 - width / 2, -py2 - bb / 2
        line_length = bbh - py1 + py2
        length = bbh
        context.move_to(main_offset, bby + bbh)
        context.rel_line_to(0, -bbh)
        context.rel_line_to(px1, py1)
        context.rel_line_to(-px1 + px2, -py1 + bbh + py2)

    context.set_fill_rule(cairo.FILL_RULE_EVEN_ODD)
    if style in ('dotted', 'dashed'):
        dash = width if style == 'dotted' else 3 * width
        if rounded1 or rounded2:
            # At least one of the two corners is rounded
            chl1 = corner_half_length(a1, b1)
            chl2 = corner_half_length(a2, b2)
            length = line_length + chl1 + chl2
            dash_length = round(length / dash)
            if rounded1 and rounded2:
                # 2x dashes
                dash = length / (dash_length + dash_length % 2)
            else:
                # 2x - 1/2 dashes
                dash = length / (dash_length + dash_length % 2 - 0.5)
            dashes1 = int(math.ceil((chl1 - dash / 2) / dash))
            dashes2 = int(math.ceil((chl2 - dash / 2) / dash))
            line = int(math.floor(line_length / dash))

            def draw_dots(dashes, line, way, x, y, px, py, chl):
                if not dashes:
                    return line + 1, 0
                for i in range(0, dashes, 2):
                    i += 0.5  # half dash
                    angle1 = (
                        ((2 * angle - way) + i * way * dash / chl)
                        / 4 * math.pi)
                    angle2 = (min if way > 0 else max)(
                        ((2 * angle - way) + (i + 1) * way * dash / chl)
                        / 4 * math.pi,
                        angle * math.pi / 2)
                    if side in ('top', 'bottom'):
                        context.move_to(x + px, main_offset + py)
                        context.line_to(
                            x + px - way * px * 1 / math.tan(angle2),
                            main_offset)
                        context.line_to(
                            x + px - way * px * 1 / math.tan(angle1),
                            main_offset)
                    elif side in ('left', 'right'):
                        context.move_to(main_offset + px, y + py)
                        context.line_to(
                            main_offset,
                            y + py + way * py * math.tan(angle2))
                        context.line_to(
                            main_offset,
                            y + py + way * py * math.tan(angle1))
                    if angle2 == angle * math.pi / 2:
                        offset = (angle1 - angle2) / ((
                            ((2 * angle - way) + (i + 1) * way * dash / chl)
                            / 4 * math.pi) - angle1)
                        line += 1
                        break
                else:
                    offset = 1 - (
                        (angle * math.pi / 2 - angle2) / (angle2 - angle1))
                return line, offset

            line, offset = draw_dots(
                dashes1, line, way, bbx, bby, px1, py1, chl1)
            line = draw_dots(
                dashes2, line, -way, bbx + bbw, bby + bbh, px2, py2, chl2)[0]

            if line_length > 1e-6:
                for i in range(0, line, 2):
                    i += offset
                    if side in ('top', 'bottom'):
                        x1 = max(bbx + px1 + i * dash, bbx + px1)
                        x2 = min(bbx + px1 + (i + 1) * dash, bbx + bbw + px2)
                        y1 = main_offset - (width if way < 0 else 0)
                        y2 = y1 + width
                    elif side in ('left', 'right'):
                        y1 = max(bby + py1 + i * dash, bby + py1)
                        y2 = min(bby + py1 + (i + 1) * dash, bby + bbh + py2)
                        x1 = main_offset - (width if way > 0 else 0)
                        x2 = x1 + width
                    context.rectangle(x1, y1, x2 - x1, y2 - y1)
        else:
            # 2x + 1 dashes
            context.clip()
            dash = length / (
                round(length / dash) - (round(length / dash) + 1) % 2) or 1
            for i in range(0, int(round(length / dash)), 2):
                if side == 'top':
                    context.rectangle(
                        bbx + i * dash, bby, dash, width)
                elif side == 'right':
                    context.rectangle(
                        bbx + bbw - width, bby + i * dash, width, dash)
                elif side == 'bottom':
                    context.rectangle(
                        bbx + i * dash, bby + bbh - width, dash, width)
                elif side == 'left':
                    context.rectangle(
                        bbx, bby + i * dash, width, dash)
    context.clip()


def draw_rounded_border(context, box, style, color):
    context.set_fill_rule(cairo.FILL_RULE_EVEN_ODD)
    rounded_box_path(context, box.rounded_padding_box())
    if style in ('ridge', 'groove'):
        rounded_box_path(context, box.rounded_box_ratio(1 / 2))
        context.set_source_rgba(*color[0])
        context.fill()
        rounded_box_path(context, box.rounded_box_ratio(1 / 2))
        rounded_box_path(context, box.rounded_border_box())
        context.set_source_rgba(*color[1])
        context.fill()
        return
    if style == 'double':
        rounded_box_path(context, box.rounded_box_ratio(1 / 3))
        rounded_box_path(context, box.rounded_box_ratio(2 / 3))
    rounded_box_path(context, box.rounded_border_box())
    context.set_source_rgba(*color)
    context.fill()


def draw_rect_border(context, box, widths, style, color):
    context.set_fill_rule(cairo.FILL_RULE_EVEN_ODD)
    bbx, bby, bbw, bbh = box
    bt, br, bb, bl = widths
    context.rectangle(*box)
    if style in ('ridge', 'groove'):
        context.rectangle(
            bbx + bl / 2, bby + bt / 2,
            bbw - (bl + br) / 2, bbh - (bt + bb) / 2)
        context.set_source_rgba(*color[0])
        context.fill()
        context.rectangle(
            bbx + bl / 2, bby + bt / 2,
            bbw - (bl + br) / 2, bbh - (bt + bb) / 2)
        context.rectangle(
            bbx + bl, bby + bt, bbw - bl - br, bbh - bt - bb)
        context.set_source_rgba(*color[1])
        context.fill()
        return
    if style == 'double':
        context.rectangle(
            bbx + bl / 3, bby + bt / 3,
            bbw - (bl + br) / 3, bbh - (bt + bb) / 3)
        context.rectangle(
            bbx + bl * 2 / 3, bby + bt * 2 / 3,
            bbw - (bl + br) * 2 / 3, bbh - (bt + bb) * 2 / 3)
    context.rectangle(bbx + bl, bby + bt, bbw - bl - br, bbh - bt - bb)
    context.set_source_rgba(*color)
    context.fill()


def draw_outlines(context, box, enable_hinting):
    width = box.style.outline_width
    color = box.style.get_color('outline_color')
    style = box.style.outline_style
    if box.style.visibility == 'visible' and width != 0 and color.alpha != 0:
        outline_box = (
            box.border_box_x() - width, box.border_box_y() - width,
            box.border_width() + 2 * width, box.border_height() + 2 * width)
        for side in SIDES:
            with stacked(context):
                clip_border_segment(
                    context, enable_hinting, style, width, side, outline_box)
                draw_rect_border(
                    context, outline_box, 4 * (width,), style,
                    styled_color(style, color, side))

    if isinstance(box, boxes.ParentBox):
        for child in box.children:
            if isinstance(child, boxes.Box):
                draw_outlines(context, child, enable_hinting)


def draw_collapsed_borders(context, table, enable_hinting):
    """Draw borders of table cells when they collapse."""
    row_heights = [row.height for row_group in table.children
                   for row in row_group.children]
    column_widths = table.column_widths
    if not (row_heights and column_widths):
        # One of the list is empty: don’t bother with empty tables
        return
    row_positions = [row.position_y for row_group in table.children
                     for row in row_group.children]
    column_positions = list(table.column_positions)
    grid_height = len(row_heights)
    grid_width = len(column_widths)
    assert grid_width == len(column_positions)
    # Add the end of the last column, but make a copy from the table attr.
    column_positions += [column_positions[-1] + column_widths[-1]]
    # Add the end of the last row. No copy here, we own this list
    row_positions.append(row_positions[-1] + row_heights[-1])
    vertical_borders, horizontal_borders = table.collapsed_border_grid
    if table.children[0].is_header:
        header_rows = len(table.children[0].children)
    else:
        header_rows = 0
    if table.children[-1].is_footer:
        footer_rows = len(table.children[-1].children)
    else:
        footer_rows = 0
    skipped_rows = table.skipped_rows
    if skipped_rows:
        body_rows_offset = skipped_rows - header_rows
    else:
        body_rows_offset = 0
    if header_rows == 0:
        header_rows = -1
    if footer_rows:
        first_footer_row = grid_height - footer_rows - 1
    else:
        first_footer_row = grid_height + 1
    original_grid_height = len(vertical_borders)
    footer_rows_offset = original_grid_height - grid_height

    def row_number(y, horizontal):
        if y < (header_rows + int(horizontal)):
            return y
        elif y >= (first_footer_row + int(horizontal)):
            return y + footer_rows_offset
        else:
            return y + body_rows_offset

    segments = []

    def half_max_width(border_list, yx_pairs, vertical=True):
        result = 0
        for y, x in yx_pairs:
            if (
                (0 <= y < grid_height and 0 <= x <= grid_width)
                if vertical else
                (0 <= y <= grid_height and 0 <= x < grid_width)
            ):
                yy = row_number(y, horizontal=not vertical)
                _, (_, width, _) = border_list[yy][x]
                result = max(result, width)
        return result / 2

    def add_vertical(x, y):
        yy = row_number(y, horizontal=False)
        score, (style, width, color) = vertical_borders[yy][x]
        if width == 0 or color.alpha == 0:
            return
        pos_x = column_positions[x]
        pos_y1 = row_positions[y] - half_max_width(horizontal_borders, [
            (y, x - 1), (y, x)], vertical=False)
        pos_y2 = row_positions[y + 1] + half_max_width(horizontal_borders, [
            (y + 1, x - 1), (y + 1, x)], vertical=False)
        segments.append((
            score, style, width, color, 'left',
            (pos_x - width / 2, pos_y1, 0, pos_y2 - pos_y1)))

    def add_horizontal(x, y):
        yy = row_number(y, horizontal=True)
        score, (style, width, color) = horizontal_borders[yy][x]
        if width == 0 or color.alpha == 0:
            return
        pos_y = row_positions[y]
        # TODO: change signs for rtl when we support rtl tables?
        pos_x1 = column_positions[x] - half_max_width(vertical_borders, [
            (y - 1, x), (y, x)])
        pos_x2 = column_positions[x + 1] + half_max_width(vertical_borders, [
            (y - 1, x + 1), (y, x + 1)])
        segments.append((
            score, style, width, color, 'top',
            (pos_x1, pos_y - width / 2, pos_x2 - pos_x1, 0)))

    for x in xrange(grid_width):
        add_horizontal(x, 0)
    for y in xrange(grid_height):
        add_vertical(0, y)
        for x in xrange(grid_width):
            add_vertical(x + 1, y)
            add_horizontal(x, y + 1)

    # Sort bigger scores last (painted later, on top)
    # Since the number of different scores is expected to be small compared
    # to the number of segments, there should be little changes and Timsort
    # should be closer to O(n) than O(n * log(n))
    segments.sort(key=operator.itemgetter(0))

    for segment in segments:
        _, style, width, color, side, border_box = segment
        if side == 'top':
            widths = (width, 0, 0, 0)
        else:
            widths = (0, 0, 0, width)
        with stacked(context):
            clip_border_segment(
                context, enable_hinting, style, width, side, border_box,
                widths)
            draw_rect_border(
                context, border_box, widths, style,
                styled_color(style, color, side))


def draw_replacedbox(context, box):
    """Draw the given :class:`boxes.ReplacedBox` to a ``cairo.context``."""
    if box.style.visibility != 'visible' or box.width == 0 or box.height == 0:
        return

    with stacked(context):
        context.translate(box.content_box_x(), box.content_box_y())
        context.rectangle(0, 0, box.width, box.height)
        context.clip()
        box.replacement.draw(
            context, box.width, box.height, box.style.image_rendering)


def draw_inline_level(context, page, box, enable_hinting):
    if isinstance(box, StackingContext):
        stacking_context = box
        assert isinstance(stacking_context.box, boxes.InlineBlockBox)
        draw_stacking_context(context, stacking_context, enable_hinting)
    else:
        draw_background(context, box.background, enable_hinting)
        draw_border(context, box, enable_hinting)
        if isinstance(box, (boxes.InlineBox, boxes.LineBox)):
            for child in box.children:
                if isinstance(child, boxes.TextBox):
                    draw_text(context, child, enable_hinting)
                else:
                    draw_inline_level(context, page, child, enable_hinting)
        elif isinstance(box, boxes.InlineReplacedBox):
            draw_replacedbox(context, box)
        else:
            assert isinstance(box, boxes.TextBox)
            # Should only happen for list markers
            draw_text(context, box, enable_hinting)


def draw_text(context, textbox, enable_hinting):
    """Draw ``textbox`` to a ``cairo.Context`` from ``PangoCairo.Context``."""
    # Pango crashes with font-size: 0
    assert textbox.style.font_size

    if textbox.style.visibility != 'visible':
        return

    context.move_to(textbox.position_x, textbox.position_y + textbox.baseline)
    context.set_source_rgba(*textbox.style.color)
    show_first_line(context, textbox.pango_layout, enable_hinting)
    values = textbox.style.text_decoration

    metrics = textbox.pango_layout.get_font_metrics()
    thickness = textbox.style.font_size / 18  # That's what other browsers do
    if enable_hinting and thickness < 1:
        thickness = 1

    if 'overline' in values:
        draw_text_decoration(
            context, textbox,
            textbox.baseline - metrics.ascent + thickness / 2,
            thickness, enable_hinting)
    if 'underline' in values:
        draw_text_decoration(
            context, textbox,
            textbox.baseline - metrics.underline_position + thickness / 2,
            thickness, enable_hinting)
    if 'line-through' in values:
        draw_text_decoration(
            context, textbox,
            textbox.baseline - metrics.strikethrough_position,
            thickness, enable_hinting)


def draw_text_decoration(context, textbox, offset_y, thickness,
                         enable_hinting):
    """Draw text-decoration of ``textbox`` to a ``cairo.Context``."""
    with stacked(context):
        if enable_hinting:
            context.set_antialias(cairo.ANTIALIAS_NONE)
        context.set_source_rgba(*textbox.style.color)
        context.set_line_width(thickness)
        context.move_to(textbox.position_x, textbox.position_y + offset_y)
        context.rel_line_to(textbox.width, 0)
        context.stroke()