ladybird/Libraries/LibWeb/Layout/LineBox.cpp

/*
 * Copyright (c) 2018-2020, Andreas Kling <andreas@ladybird.org>
 * Copyright (c) 2025, Jelle Raaijmakers <jelle@ladybird.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/CharacterTypes.h>
#include <AK/Utf8View.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/DOM/Position.h>
#include <LibWeb/Layout/Box.h>
#include <LibWeb/Layout/LineBox.h>
#include <LibWeb/Layout/Node.h>
#include <LibWeb/Layout/TextNode.h>

namespace Web::Layout {

CSSPixels LineBox::width() const
{
    if (m_writing_mode != CSS::WritingMode::HorizontalTb)
        return m_block_length;
    return m_inline_length;
}

CSSPixels LineBox::height() const
{
    if (m_writing_mode != CSS::WritingMode::HorizontalTb)
        return m_inline_length;
    return m_block_length;
}

CSSPixels LineBox::bottom() const
{
    if (m_writing_mode != CSS::WritingMode::HorizontalTb)
        return m_inline_length;
    return m_bottom;
}

void LineBox::add_fragment(Node const& layout_node, size_t start, size_t length, CSSPixels leading_size,
    CSSPixels trailing_size, CSSPixels leading_margin, CSSPixels trailing_margin, CSSPixels content_width,
    CSSPixels content_height, CSSPixels border_box_top, CSSPixels border_box_bottom, RefPtr<Gfx::GlyphRun> glyph_run)
{
    bool text_align_is_justify = layout_node.computed_values().text_align() == CSS::TextAlign::Justify;
    if (glyph_run && !text_align_is_justify && !m_fragments.is_empty()
        && &m_fragments.last().layout_node() == &layout_node
        && &m_fragments.last().m_glyph_run->font() == &glyph_run->font()
        && m_fragments.last().start() + m_fragments.last().length_in_code_units() == start) {
        // The fragment we're adding is from the last Layout::Node on the line.
        // Expand the last fragment instead of adding a new one with the same Layout::Node.
        m_fragments.last().m_length_in_code_units += length;
        m_fragments.last().append_glyph_run(glyph_run, content_width);
    } else {
        CSSPixels inline_offset = leading_margin + leading_size + m_inline_length;
        CSSPixels block_offset = 0;
        m_fragments.append(LineBoxFragment { layout_node, start, length, inline_offset, block_offset, content_width,
            content_height, border_box_top, m_direction, m_writing_mode, move(glyph_run) });
    }
    m_inline_length += leading_margin + leading_size + content_width + trailing_size + trailing_margin;
    m_block_length = max(m_block_length, content_height + border_box_top + border_box_bottom);
}

void LineBox::add_static_position_marker(Box const& box)
{
    m_static_position_markers.append(StaticPositionMarker {
        .box = &box,
        .inline_offset = m_inline_length,
        .block_offset = 0,
        .writing_mode = m_writing_mode,
    });
}

void LineBox::clamp_static_position_markers_to_inline_length()
{
    for (auto& marker : m_static_position_markers) {
        if (marker.inline_offset > m_inline_length)
            marker.inline_offset = m_inline_length;
    }
}

CSSPixels LineBox::calculate_or_trim_trailing_whitespace(RemoveTrailingWhitespace should_remove)
{
    auto should_trim = [](LineBoxFragment* fragment) {
        auto white_space_collapse = fragment->layout_node().computed_values().white_space_collapse();

        return white_space_collapse == CSS::WhiteSpaceCollapse::Collapse || white_space_collapse == CSS::WhiteSpaceCollapse::PreserveBreaks;
    };

    CSSPixels whitespace_width = 0;
    CSSPixels trailing_whitespace_width = 0;
    LineBoxFragment* last_fragment = nullptr;
    size_t fragment_index = m_fragments.size();
    for (;;) {
        if (fragment_index == 0)
            return whitespace_width;

        last_fragment = &m_fragments[--fragment_index];
        if (auto const* dom_node = last_fragment->layout_node().dom_node()) {
            auto cursor_position = dom_node->document().cursor_position();
            if (cursor_position && cursor_position->node() == dom_node)
                return whitespace_width;
        }
        if (!should_trim(last_fragment))
            return whitespace_width;
        if (!last_fragment->is_justifiable_whitespace())
            break;

        whitespace_width += last_fragment->inline_length();
        trailing_whitespace_width += last_fragment->inline_length();
        if (should_remove == RemoveTrailingWhitespace::Yes) {
            m_inline_length -= last_fragment->inline_length();
            m_fragments.remove(fragment_index);
            clamp_static_position_markers_to_inline_length();
        }
    }

    auto last_text = last_fragment->text();
    if (last_text.is_empty()) {
        // No text to trim, but we may have removed whitespace-only fragments.
        if (should_remove == RemoveTrailingWhitespace::Yes && trailing_whitespace_width > 0)
            last_fragment->set_has_trailing_whitespace(true);
        return whitespace_width;
    }

    // Trim trailing whitespace characters from the last fragment.
    size_t last_text_length = last_text.length_in_code_units();
    while (last_text_length) {
        auto last_character = last_text.code_unit_at(--last_text_length);
        if (!is_ascii_space(last_character))
            break;

        auto const& font = last_fragment->glyph_run() ? last_fragment->glyph_run()->font() : last_fragment->layout_node().first_available_font();
        CSSPixels last_character_width = CSSPixels(font.glyph_width(last_character)) + last_fragment->layout_node().computed_values().letter_spacing();
        whitespace_width += last_character_width;
        trailing_whitespace_width += last_character_width;
        if (should_remove == RemoveTrailingWhitespace::Yes) {
            --last_fragment->m_length_in_code_units;
            last_fragment->set_inline_length(last_fragment->inline_length() - last_character_width);
            m_inline_length -= last_character_width;
            clamp_static_position_markers_to_inline_length();
        }
    }

    // Track trimmed whitespace for selection purposes, but don't overwrite a value
    // that was already set during line breaking (for wrapped lines).
    if (should_remove == RemoveTrailingWhitespace::Yes
        && (trailing_whitespace_width > 0 || !last_fragment->has_trailing_whitespace())) {
        last_fragment->set_has_trailing_whitespace(trailing_whitespace_width > 0);
    }

    return whitespace_width;
}

CSSPixels LineBox::get_trailing_whitespace_width() const
{
    return const_cast<LineBox&>(*this).calculate_or_trim_trailing_whitespace(RemoveTrailingWhitespace::No);
}

void LineBox::trim_trailing_whitespace()
{
    calculate_or_trim_trailing_whitespace(RemoveTrailingWhitespace::Yes);
}

bool LineBox::is_empty_or_ends_in_whitespace() const
{
    if (m_fragments.is_empty())
        return true;

    return m_fragments.last().ends_in_whitespace();
}

}