ladybird/Libraries/LibWeb/Layout/FormattingContext.cpp

/*
 * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <LibWeb/Dump.h>
#include <LibWeb/Layout/BlockBox.h>
#include <LibWeb/Layout/BlockFormattingContext.h>
#include <LibWeb/Layout/Box.h>
#include <LibWeb/Layout/FormattingContext.h>
#include <LibWeb/Layout/InlineFormattingContext.h>
#include <LibWeb/Layout/ReplacedBox.h>
#include <LibWeb/Layout/TableFormattingContext.h>

namespace Web::Layout {

FormattingContext::FormattingContext(Box& context_box, FormattingContext* parent)
    : m_parent(parent)
    , m_context_box(&context_box)
{
}

FormattingContext::~FormattingContext()
{
}

bool FormattingContext::creates_block_formatting_context(const Box& box)
{
    if (box.is_root_element())
        return true;
    if (box.is_floating())
        return true;
    if (box.is_absolutely_positioned())
        return true;
    if (box.is_inline_block())
        return true;
    if (box.is_table_cell())
        return true;
    // FIXME: table-caption
    // FIXME: anonymous table cells
    // FIXME: Block elements where overflow has a value other than visible and clip.
    // FIXME: display: flow-root
    // FIXME: Elements with contain: layout, content, or paint.
    // FIXME: flex
    // FIXME: grid
    // FIXME: multicol
    // FIXME: column-span: all
    return false;
}

void FormattingContext::layout_inside(Box& box, LayoutMode layout_mode)
{
    if (creates_block_formatting_context(box)) {
        BlockFormattingContext context(box, this);
        context.run(box, layout_mode);
        return;
    }
    if (box.is_table()) {
        TableFormattingContext context(box, this);
        context.run(box, layout_mode);
    } else if (box.children_are_inline()) {
        InlineFormattingContext context(box, this);
        context.run(box, layout_mode);
    } else {
        // FIXME: This needs refactoring!
        ASSERT(is_block_formatting_context());
        run(box, layout_mode);
    }
}

static float greatest_child_width(const Box& box)
{
    float max_width = 0;
    if (box.children_are_inline()) {
        for (auto& child : box.line_boxes()) {
            max_width = max(max_width, child.width());
        }
    } else {
        box.for_each_child_of_type<Box>([&](auto& child) {
            max_width = max(max_width, child.border_box_width());
        });
    }
    return max_width;
}

FormattingContext::ShrinkToFitResult FormattingContext::calculate_shrink_to_fit_widths(Box& box)
{
    // Calculate the preferred width by formatting the content without breaking lines
    // other than where explicit line breaks occur.
    layout_inside(box, LayoutMode::OnlyRequiredLineBreaks);
    float preferred_width = greatest_child_width(box);

    // Also calculate the preferred minimum width, e.g., by trying all possible line breaks.
    // CSS 2.2 does not define the exact algorithm.

    layout_inside(box, LayoutMode::AllPossibleLineBreaks);
    float preferred_minimum_width = greatest_child_width(box);

    return { preferred_width, preferred_minimum_width };
}

static Gfx::FloatSize solve_replaced_size_constraint(float w, float h, const ReplacedBox& box)
{
    // 10.4 Minimum and maximum widths: 'min-width' and 'max-width'

    auto& containing_block = *box.containing_block();
    auto specified_min_width = box.style().min_width().resolved_or_zero(box, containing_block.width()).to_px(box);
    auto specified_max_width = box.style().max_width().resolved(CSS::Length::make_px(w), box, containing_block.width()).to_px(box);
    auto specified_min_height = box.style().min_height().resolved_or_auto(box, containing_block.height()).to_px(box);
    auto specified_max_height = box.style().max_height().resolved(CSS::Length::make_px(h), box, containing_block.height()).to_px(box);

    auto min_width = min(specified_min_width, specified_max_width);
    auto max_width = max(specified_min_width, specified_max_width);
    auto min_height = min(specified_min_height, specified_max_height);
    auto max_height = max(specified_min_height, specified_max_height);

    if (w > max_width)
        return { w, max(max_width * h / w, min_height) };
    if (w < min_width)
        return { max_width, min(min_width * h / w, max_height) };
    if (h > max_height)
        return { max(max_height * w / h, min_width), max_height };
    if (h < min_height)
        return { min(min_height * w / h, max_width), min_height };
    if ((w > max_width && h > max_height) && (max_width / w < max_height / h))
        return { max_width, max(min_height, max_width * h / w) };
    if ((w > max_width && h > max_height) && (max_width / w > max_height / h))
        return { max(min_width, max_height * w / h), max_height };
    if ((w < min_width && h < min_height) && (min_width / w < min_height / h))
        return { min(max_width, min_height * w / h), min_height };
    if ((w < min_width && h < min_height) && (min_width / w > min_height / h))
        return { min_width, min(max_height, min_width * h / w) };
    if (w < min_width && h > max_height)
        return { min_width, max_height };
    if (w > max_width && h < min_height)
        return { max_width, min_height };
    return { w, h };
}

float FormattingContext::tentative_width_for_replaced_element(const ReplacedBox& box, const CSS::Length& width)
{
    auto& containing_block = *box.containing_block();
    auto specified_height = box.style().height().resolved_or_auto(box, containing_block.height());

    float used_width = width.to_px(box);

    // If 'height' and 'width' both have computed values of 'auto' and the element also has an intrinsic width,
    // then that intrinsic width is the used value of 'width'.
    if (specified_height.is_auto() && width.is_auto() && box.has_intrinsic_width()) {
        used_width = box.intrinsic_width();
    }

    // If 'height' and 'width' both have computed values of 'auto' and the element has no intrinsic width,
    // but does have an intrinsic height and intrinsic ratio;
    // or if 'width' has a computed value of 'auto',
    // 'height' has some other computed value, and the element does have an intrinsic ratio; then the used value of 'width' is:
    //
    //     (used height) * (intrinsic ratio)
    else if ((specified_height.is_auto() && width.is_auto() && !box.has_intrinsic_width() && box.has_intrinsic_height() && box.has_intrinsic_ratio()) || (width.is_auto() && box.has_intrinsic_ratio())) {
        used_width = compute_height_for_replaced_element(box) * box.intrinsic_ratio();
    }

    else if (width.is_auto() && box.has_intrinsic_width()) {
        used_width = box.intrinsic_width();
    }

    else if (width.is_auto()) {
        used_width = 300;
    }

    return used_width;
}

float FormattingContext::compute_width_for_replaced_element(const ReplacedBox& box)
{
    // 10.3.4 Block-level, replaced elements in normal flow...
    // 10.3.2 Inline, replaced elements

    auto zero_value = CSS::Length::make_px(0);
    auto& containing_block = *box.containing_block();

    auto margin_left = box.style().margin().left.resolved_or_zero(box, containing_block.width());
    auto margin_right = box.style().margin().right.resolved_or_zero(box, containing_block.width());

    // A computed value of 'auto' for 'margin-left' or 'margin-right' becomes a used value of '0'.
    if (margin_left.is_auto())
        margin_left = zero_value;
    if (margin_right.is_auto())
        margin_right = zero_value;

    auto specified_width = box.style().width().resolved_or_auto(box, containing_block.width());

    // 1. The tentative used width is calculated (without 'min-width' and 'max-width')
    auto used_width = tentative_width_for_replaced_element(box, specified_width);

    // 2. The tentative used width is greater than 'max-width', the rules above are applied again,
    //    but this time using the computed value of 'max-width' as the computed value for 'width'.
    auto specified_max_width = box.style().max_width().resolved_or_auto(box, containing_block.width());
    if (!specified_max_width.is_auto()) {
        if (used_width > specified_max_width.to_px(box)) {
            used_width = tentative_width_for_replaced_element(box, specified_max_width);
        }
    }

    // 3. If the resulting width is smaller than 'min-width', the rules above are applied again,
    //    but this time using the value of 'min-width' as the computed value for 'width'.
    auto specified_min_width = box.style().min_width().resolved_or_auto(box, containing_block.width());
    if (!specified_min_width.is_auto()) {
        if (used_width < specified_min_width.to_px(box)) {
            used_width = tentative_width_for_replaced_element(box, specified_min_width);
        }
    }

    return used_width;
}

float FormattingContext::tentative_height_for_replaced_element(const ReplacedBox& box, const CSS::Length& height)
{
    auto& containing_block = *box.containing_block();
    auto specified_width = box.style().width().resolved_or_auto(box, containing_block.width());

    float used_height = height.to_px(box);

    // If 'height' and 'width' both have computed values of 'auto' and the element also has
    // an intrinsic height, then that intrinsic height is the used value of 'height'.
    if (specified_width.is_auto() && height.is_auto() && box.has_intrinsic_height())
        used_height = box.intrinsic_height();
    else if (height.is_auto() && box.has_intrinsic_ratio())
        used_height = compute_width_for_replaced_element(box) / box.intrinsic_ratio();
    else if (height.is_auto() && box.has_intrinsic_height())
        used_height = box.intrinsic_height();
    else if (height.is_auto())
        used_height = 150;

    return used_height;
}

float FormattingContext::compute_height_for_replaced_element(const ReplacedBox& box)
{
    // 10.6.2 Inline replaced elements, block-level replaced elements in normal flow,
    // 'inline-block' replaced elements in normal flow and floating replaced elements

    auto& containing_block = *box.containing_block();
    auto specified_width = box.style().width().resolved_or_auto(box, containing_block.width());
    auto specified_height = box.style().height().resolved_or_auto(box, containing_block.height());

    float used_height = tentative_height_for_replaced_element(box, specified_height);

    if (specified_width.is_auto() && specified_height.is_auto() && box.has_intrinsic_ratio()) {
        float w = tentative_width_for_replaced_element(box, specified_width);
        float h = used_height;
        used_height = solve_replaced_size_constraint(w, h, box).height();
    }

    return used_height;
}

}