ladybird/Userland/Libraries/LibWeb/Painting/DisplayList.cpp

/*
 * Copyright (c) 2024, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibWeb/Painting/DisplayList.h>

namespace Web::Painting {

void DisplayList::append(Command&& command, Optional<i32> scroll_frame_id)
{
    m_commands.append({ scroll_frame_id, move(command) });
}

static Optional<Gfx::IntRect> command_bounding_rectangle(Command const& command)
{
    return command.visit(
        [&](auto const& command) -> Optional<Gfx::IntRect> {
            if constexpr (requires { command.bounding_rect(); })
                return command.bounding_rect();
            else
                return {};
        });
}

void DisplayList::apply_scroll_offsets(Vector<Gfx::IntPoint> const& offsets_by_frame_id)
{
    for (auto& command_with_scroll_id : m_commands) {
        if (command_with_scroll_id.scroll_frame_id.has_value()) {
            auto const& scroll_frame_id = command_with_scroll_id.scroll_frame_id.value();
            auto const& scroll_offset = offsets_by_frame_id[scroll_frame_id];
            command_with_scroll_id.command.visit(
                [&](auto& command) {
                    if constexpr (requires { command.translate_by(scroll_offset); })
                        command.translate_by(scroll_offset);
                });
        }
    }
}

void DisplayList::mark_unnecessary_commands()
{
    // The pair sample_under_corners and blit_corner_clipping commands is not needed if there are no painting commands
    // in between them that produce visible output.
    struct SampleCornersBlitCornersRange {
        u32 sample_command_index;
        bool has_painting_commands_in_between { false };
    };
    // Stack of sample_under_corners commands that have not been matched with a blit_corner_clipping command yet.
    Vector<SampleCornersBlitCornersRange> sample_blit_ranges;
    for (u32 command_index = 0; command_index < m_commands.size(); ++command_index) {
        auto const& command = m_commands[command_index].command;
        if (command.has<SampleUnderCorners>()) {
            sample_blit_ranges.append({
                .sample_command_index = command_index,
                .has_painting_commands_in_between = false,
            });
        } else if (command.has<BlitCornerClipping>()) {
            auto range = sample_blit_ranges.take_last();
            if (!range.has_painting_commands_in_between) {
                m_commands[range.sample_command_index].skip = true;
                m_commands[command_index].skip = true;
            }
        } else {
            // Save, Restore and AddClipRect commands do not produce visible output
            auto update_clip_command = command.has<Save>() || command.has<Restore>() || command.has<AddClipRect>();
            if (sample_blit_ranges.size() > 0 && !update_clip_command) {
                // If painting command is found for sample_under_corners command on top of the stack, then all
                // sample_under_corners commands below should also not be skipped.
                for (auto& sample_blit_range : sample_blit_ranges)
                    sample_blit_range.has_painting_commands_in_between = true;
            }
        }
    }
    VERIFY(sample_blit_ranges.is_empty());
}

void DisplayListPlayer::execute(DisplayList& display_list)
{
    auto const& commands = display_list.commands();

    HashTable<u32> skipped_sample_corner_commands;
    size_t next_command_index = 0;
    while (next_command_index < commands.size()) {
        if (commands[next_command_index].skip) {
            next_command_index++;
            continue;
        }

        auto& command = commands[next_command_index++].command;
        auto bounding_rect = command_bounding_rectangle(command);
        if (bounding_rect.has_value() && (bounding_rect->is_empty() || would_be_fully_clipped_by_painter(*bounding_rect))) {
            if (command.has<SampleUnderCorners>()) {
                auto const& sample_under_corners = command.get<SampleUnderCorners>();
                skipped_sample_corner_commands.set(sample_under_corners.id);
            }
            continue;
        }

        if (command.has<BlitCornerClipping>()) {
            auto const& blit_corner_clipping = command.get<BlitCornerClipping>();
            // FIXME: If a sampling command falls outside the viewport and is not executed, the associated blit
            //        should also be skipped if it is within the viewport. In a properly generated list of
            //        painting commands, sample and blit commands should have matching rectangles, preventing
            //        this discrepancy.
            if (skipped_sample_corner_commands.contains(blit_corner_clipping.id)) {
                dbgln("Skipping blit_corner_clipping command because the sample_under_corners command was skipped.");
                continue;
            }
        }

#define HANDLE_COMMAND(command_type, executor_method) \
    if (command.has<command_type>()) {                \
        executor_method(command.get<command_type>()); \
    }

        // clang-format off
        HANDLE_COMMAND(DrawGlyphRun, draw_glyph_run)
        else HANDLE_COMMAND(FillRect, fill_rect)
        else HANDLE_COMMAND(DrawScaledBitmap, draw_scaled_bitmap)
        else HANDLE_COMMAND(DrawScaledImmutableBitmap, draw_scaled_immutable_bitmap)
        else HANDLE_COMMAND(DrawRepeatedImmutableBitmap, draw_repeated_immutable_bitmap)
        else HANDLE_COMMAND(AddClipRect, add_clip_rect)
        else HANDLE_COMMAND(Save, save)
        else HANDLE_COMMAND(Restore, restore)
        else HANDLE_COMMAND(PushStackingContext, push_stacking_context)
        else HANDLE_COMMAND(PopStackingContext, pop_stacking_context)
        else HANDLE_COMMAND(PaintLinearGradient, paint_linear_gradient)
        else HANDLE_COMMAND(PaintRadialGradient, paint_radial_gradient)
        else HANDLE_COMMAND(PaintConicGradient, paint_conic_gradient)
        else HANDLE_COMMAND(PaintOuterBoxShadow, paint_outer_box_shadow)
        else HANDLE_COMMAND(PaintInnerBoxShadow, paint_inner_box_shadow)
        else HANDLE_COMMAND(PaintTextShadow, paint_text_shadow)
        else HANDLE_COMMAND(FillRectWithRoundedCorners, fill_rect_with_rounded_corners)
        else HANDLE_COMMAND(FillPathUsingColor, fill_path_using_color)
        else HANDLE_COMMAND(FillPathUsingPaintStyle, fill_path_using_paint_style)
        else HANDLE_COMMAND(StrokePathUsingColor, stroke_path_using_color)
        else HANDLE_COMMAND(StrokePathUsingPaintStyle, stroke_path_using_paint_style)
        else HANDLE_COMMAND(DrawEllipse, draw_ellipse)
        else HANDLE_COMMAND(FillEllipse, fill_ellipse)
        else HANDLE_COMMAND(DrawLine, draw_line)
        else HANDLE_COMMAND(ApplyBackdropFilter, apply_backdrop_filter)
        else HANDLE_COMMAND(DrawRect, draw_rect)
        else HANDLE_COMMAND(DrawTriangleWave, draw_triangle_wave)
        else HANDLE_COMMAND(SampleUnderCorners, sample_under_corners)
        else HANDLE_COMMAND(BlitCornerClipping, blit_corner_clipping)
        else VERIFY_NOT_REACHED();
        // clang-format on
    }
}

}