serenity/Userland/Libraries/LibWeb/Layout/TextNode.cpp

/*
 * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/ScopeGuard.h>
#include <AK/StringBuilder.h>
#include <LibGfx/Painter.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/Layout/BlockBox.h>
#include <LibWeb/Layout/InlineFormattingContext.h>
#include <LibWeb/Layout/Label.h>
#include <LibWeb/Layout/TextNode.h>
#include <LibWeb/Page/Frame.h>
#include <ctype.h>

namespace Web::Layout {

TextNode::TextNode(DOM::Document& document, DOM::Text& text)
    : Node(document, &text)
{
    set_inline(true);
}

TextNode::~TextNode()
{
}

static bool is_all_whitespace(const StringView& string)
{
    for (size_t i = 0; i < string.length(); ++i) {
        if (!isspace(string[i]))
            return false;
    }
    return true;
}

void TextNode::paint_fragment(PaintContext& context, const LineBoxFragment& fragment, PaintPhase phase) const
{
    auto& painter = context.painter();

    if (phase == PaintPhase::Background) {
        painter.fill_rect(enclosing_int_rect(fragment.absolute_rect()), computed_values().background_color());
    }

    if (phase == PaintPhase::Foreground) {
        painter.set_font(font());

        if (document().inspected_node() == &dom_node())
            context.painter().draw_rect(enclosing_int_rect(fragment.absolute_rect()), Color::Magenta);

        if (computed_values().text_decoration_line() == CSS::TextDecorationLine::Underline)
            painter.draw_line(enclosing_int_rect(fragment.absolute_rect()).bottom_left().translated(0, 1), enclosing_int_rect(fragment.absolute_rect()).bottom_right().translated(0, 1), computed_values().color());

        // FIXME: text-transform should be done already in layout, since uppercase glyphs may be wider than lowercase, etc.
        auto text = m_text_for_rendering;
        auto text_transform = computed_values().text_transform();
        if (text_transform == CSS::TextTransform::Uppercase)
            text = m_text_for_rendering.to_uppercase();
        if (text_transform == CSS::TextTransform::Lowercase)
            text = m_text_for_rendering.to_lowercase();

        painter.draw_text(enclosing_int_rect(fragment.absolute_rect()), text.substring_view(fragment.start(), fragment.length()), Gfx::TextAlignment::CenterLeft, computed_values().color());

        auto selection_rect = fragment.selection_rect(font());
        if (!selection_rect.is_empty()) {
            painter.fill_rect(enclosing_int_rect(selection_rect), context.palette().selection());
            Gfx::PainterStateSaver saver(painter);
            painter.add_clip_rect(enclosing_int_rect(selection_rect));
            painter.draw_text(enclosing_int_rect(fragment.absolute_rect()), text.substring_view(fragment.start(), fragment.length()), Gfx::TextAlignment::CenterLeft, context.palette().selection_text());
        }

        paint_cursor_if_needed(context, fragment);
    }
}

void TextNode::paint_cursor_if_needed(PaintContext& context, const LineBoxFragment& fragment) const
{
    if (!frame().is_focused_frame())
        return;

    if (!frame().cursor_blink_state())
        return;

    if (frame().cursor_position().node() != &dom_node())
        return;

    if (!(frame().cursor_position().offset() >= (unsigned)fragment.start() && frame().cursor_position().offset() < (unsigned)(fragment.start() + fragment.length())))
        return;

    if (!fragment.layout_node().dom_node() || !fragment.layout_node().dom_node()->is_editable())
        return;

    auto fragment_rect = fragment.absolute_rect();

    float cursor_x = fragment_rect.x() + font().width(fragment.text().substring_view(0, frame().cursor_position().offset() - fragment.start()));
    float cursor_top = fragment_rect.top();
    float cursor_height = fragment_rect.height();
    Gfx::IntRect cursor_rect(cursor_x, cursor_top, 1, cursor_height);

    context.painter().draw_rect(cursor_rect, computed_values().color());
}

void TextNode::compute_text_for_rendering(bool collapse, bool previous_is_empty_or_ends_in_whitespace)
{
    if (!collapse) {
        m_text_for_rendering = dom_node().data();
        return;
    }

    // Collapse whitespace into single spaces
    auto utf8_view = Utf8View(dom_node().data());
    StringBuilder builder(dom_node().data().length());
    auto it = utf8_view.begin();
    auto skip_over_whitespace = [&] {
        auto prev = it;
        while (it != utf8_view.end() && isspace(*it)) {
            prev = it;
            ++it;
        }
        it = prev;
    };
    if (previous_is_empty_or_ends_in_whitespace)
        skip_over_whitespace();
    for (; it != utf8_view.end(); ++it) {
        if (!isspace(*it)) {
            builder.append(utf8_view.as_string().characters_without_null_termination() + utf8_view.byte_offset_of(it), it.code_point_length_in_bytes());
        } else {
            builder.append(' ');
            skip_over_whitespace();
        }
    }
    m_text_for_rendering = builder.to_string();
}

void TextNode::split_into_lines_by_rules(InlineFormattingContext& context, LayoutMode layout_mode, bool do_collapse, bool do_wrap_lines, bool do_wrap_breaks)
{
    auto& containing_block = context.containing_block();

    auto& font = this->font();

    auto& line_boxes = containing_block.line_boxes();
    containing_block.ensure_last_line_box();
    float available_width = context.available_width_at_line(line_boxes.size() - 1) - line_boxes.last().width();

    compute_text_for_rendering(do_collapse, line_boxes.last().is_empty_or_ends_in_whitespace());
    ChunkIterator iterator(m_text_for_rendering, layout_mode, do_wrap_lines, do_wrap_breaks);

    for (;;) {
        auto chunk_opt = iterator.next();
        if (!chunk_opt.has_value())
            break;
        auto& chunk = chunk_opt.value();

        // Collapse entire fragment into non-existence if previous fragment on line ended in whitespace.
        if (do_collapse && line_boxes.last().is_empty_or_ends_in_whitespace() && chunk.is_all_whitespace)
            continue;

        float chunk_width;
        if (do_wrap_lines) {
            if (do_collapse && isspace(*chunk.view.begin()) && line_boxes.last().is_empty_or_ends_in_whitespace()) {
                // This is a non-empty chunk that starts with collapsible whitespace.
                // We are at either at the start of a new line, or after something that ended in whitespace,
                // so we don't need to contribute our own whitespace to the line. Skip over it instead!
                ++chunk.start;
                --chunk.length;
                chunk.view = chunk.view.substring_view(1, chunk.view.byte_length() - 1);
            }

            chunk_width = font.width(chunk.view) + font.glyph_spacing();

            if (line_boxes.last().width() > 0 && chunk_width > available_width) {
                containing_block.add_line_box();
                available_width = context.available_width_at_line(line_boxes.size() - 1);

                if (do_collapse && chunk.is_all_whitespace)
                    continue;
            }
        } else {
            chunk_width = font.width(chunk.view);
        }

        line_boxes.last().add_fragment(*this, chunk.start, chunk.length, chunk_width, font.glyph_height());
        available_width -= chunk_width;

        if (do_wrap_lines && available_width < 0) {
            containing_block.add_line_box();
            available_width = context.available_width_at_line(line_boxes.size() - 1);
        }

        if (do_wrap_breaks && chunk.has_breaking_newline) {
            containing_block.add_line_box();
            available_width = context.available_width_at_line(line_boxes.size() - 1);
        }
    }
}

void TextNode::split_into_lines(InlineFormattingContext& context, LayoutMode layout_mode)
{
    bool do_collapse = true;
    bool do_wrap_lines = true;
    bool do_wrap_breaks = false;

    if (computed_values().white_space() == CSS::WhiteSpace::Nowrap) {
        do_collapse = true;
        do_wrap_lines = false;
        do_wrap_breaks = false;
    } else if (computed_values().white_space() == CSS::WhiteSpace::Pre) {
        do_collapse = false;
        do_wrap_lines = false;
        do_wrap_breaks = true;
    } else if (computed_values().white_space() == CSS::WhiteSpace::PreLine) {
        do_collapse = true;
        do_wrap_lines = true;
        do_wrap_breaks = true;
    } else if (computed_values().white_space() == CSS::WhiteSpace::PreWrap) {
        do_collapse = false;
        do_wrap_lines = true;
        do_wrap_breaks = true;
    }

    split_into_lines_by_rules(context, layout_mode, do_collapse, do_wrap_lines, do_wrap_breaks);
}

bool TextNode::wants_mouse_events() const
{
    return parent() && is<Label>(parent());
}

void TextNode::handle_mousedown(Badge<EventHandler>, const Gfx::IntPoint& position, unsigned button, unsigned)
{
    if (!parent() || !is<Label>(*parent()))
        return;
    downcast<Label>(*parent()).handle_mousedown_on_label({}, position, button);
    frame().event_handler().set_mouse_event_tracking_layout_node(this);
}

void TextNode::handle_mouseup(Badge<EventHandler>, const Gfx::IntPoint& position, unsigned button, unsigned)
{
    if (!parent() || !is<Label>(*parent()))
        return;

    // NOTE: Changing the state of the DOM node may run arbitrary JS, which could disappear this node.
    NonnullRefPtr protect = *this;

    downcast<Label>(*parent()).handle_mouseup_on_label({}, position, button);
    frame().event_handler().set_mouse_event_tracking_layout_node(nullptr);
}

void TextNode::handle_mousemove(Badge<EventHandler>, const Gfx::IntPoint& position, unsigned button, unsigned)
{
    if (!parent() || !is<Label>(*parent()))
        return;
    downcast<Label>(*parent()).handle_mousemove_on_label({}, position, button);
}

TextNode::ChunkIterator::ChunkIterator(StringView const& text, LayoutMode layout_mode, bool wrap_lines, bool wrap_breaks)
    : m_layout_mode(layout_mode)
    , m_wrap_lines(wrap_lines)
    , m_wrap_breaks(wrap_breaks)
    , m_utf8_view(text)
    , m_start_of_chunk(m_utf8_view.begin())
    , m_iterator(m_utf8_view.begin())
{
    m_last_was_space = !text.is_empty() && isspace(*m_utf8_view.begin());
}

Optional<TextNode::Chunk> TextNode::ChunkIterator::next()
{
    while (m_iterator != m_utf8_view.end()) {
        auto guard = ScopeGuard([&] { ++m_iterator; });
        if (m_layout_mode == LayoutMode::AllPossibleLineBreaks) {
            if (auto result = try_commit_chunk(m_iterator, false); result.has_value())
                return result.release_value();
        }
        if (m_last_was_newline) {
            m_last_was_newline = false;
            if (auto result = try_commit_chunk(m_iterator, true); result.has_value())
                return result.release_value();
        }
        if (m_wrap_breaks && *m_iterator == '\n') {
            m_last_was_newline = true;
            if (auto result = try_commit_chunk(m_iterator, false); result.has_value())
                return result.release_value();
        }
        if (m_wrap_lines) {
            bool is_space = isspace(*m_iterator);
            if (is_space != m_last_was_space) {
                m_last_was_space = is_space;
                if (auto result = try_commit_chunk(m_iterator, false); result.has_value())
                    return result.release_value();
            }
        }
    }

    if (m_last_was_newline) {
        m_last_was_newline = false;
        if (auto result = try_commit_chunk(m_utf8_view.end(), true); result.has_value())
            return result.release_value();
    }
    if (m_start_of_chunk != m_utf8_view.end()) {
        if (auto result = try_commit_chunk(m_utf8_view.end(), false, true); result.has_value())
            return result.release_value();
    }

    return {};
}

Optional<TextNode::Chunk> TextNode::ChunkIterator::try_commit_chunk(Utf8View::Iterator const& it, bool has_breaking_newline, bool must_commit)
{
    if (m_layout_mode == LayoutMode::OnlyRequiredLineBreaks && !must_commit)
        return {};

    auto start = m_utf8_view.byte_offset_of(m_start_of_chunk);
    auto length = m_utf8_view.byte_offset_of(it) - m_utf8_view.byte_offset_of(m_start_of_chunk);

    if (has_breaking_newline || length > 0) {
        auto chunk_view = m_utf8_view.substring_view(start, length);
        m_start_of_chunk = it;
        return Chunk {
            .view = chunk_view,
            .start = start,
            .length = length,
            .has_breaking_newline = has_breaking_newline,
            .is_all_whitespace = is_all_whitespace(chunk_view.as_string()),
        };
    }

    m_start_of_chunk = it;
    return {};
}

}