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

/*
 * Copyright (c) 2022, MacDue <macdue@dueutil.tech>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibGfx/Bitmap.h>
#include <LibGfx/Painter.h>
#include <LibWeb/Painting/BorderRadiusCornerClipper.h>

namespace Web::Painting {

ErrorOr<BorderRadiusCornerClipper> BorderRadiusCornerClipper::create(Gfx::IntRect const& border_rect, BorderRadiiData const& border_radii, CornerClip corner_clip)
{
    VERIFY(border_radii.has_any_radius());

    auto top_left = border_radii.top_left.as_corner();
    auto top_right = border_radii.top_right.as_corner();
    auto bottom_right = border_radii.bottom_right.as_corner();
    auto bottom_left = border_radii.bottom_left.as_corner();

    Gfx::IntSize corners_bitmap_size {
        max(
            top_left.horizontal_radius + top_right.horizontal_radius,
            bottom_left.horizontal_radius + bottom_right.horizontal_radius),
        max(
            top_left.vertical_radius + bottom_left.vertical_radius,
            top_right.vertical_radius + bottom_right.vertical_radius)
    };

    auto corner_bitmap = get_cached_corner_bitmap(corners_bitmap_size);
    if (!corner_bitmap)
        return Error::from_errno(ENOMEM);

    CornerData corner_data {
        .corner_radii = {
            .top_left = top_left,
            .top_right = top_right,
            .bottom_right = bottom_right,
            .bottom_left = bottom_left },
        .page_locations = { .top_left = border_rect.top_left(), .top_right = border_rect.top_right().translated(-top_right.horizontal_radius + 1, 0), .bottom_right = border_rect.bottom_right().translated(-bottom_right.horizontal_radius + 1, -bottom_right.vertical_radius + 1), .bottom_left = border_rect.bottom_left().translated(0, -bottom_left.vertical_radius + 1) },
        .bitmap_locations = { .top_left = { 0, 0 }, .top_right = { corners_bitmap_size.width() - top_right.horizontal_radius, 0 }, .bottom_right = { corners_bitmap_size.width() - bottom_right.horizontal_radius, corners_bitmap_size.height() - bottom_right.vertical_radius }, .bottom_left = { 0, corners_bitmap_size.height() - bottom_left.vertical_radius } },
        .corner_bitmap_size = corners_bitmap_size
    };

    return BorderRadiusCornerClipper { corner_data, corner_bitmap.release_nonnull(), corner_clip };
}

void BorderRadiusCornerClipper::sample_under_corners(Gfx::Painter& page_painter)
{
    // Generate a mask for the corners:
    Gfx::Painter corner_painter { *m_corner_bitmap };
    Gfx::AntiAliasingPainter corner_aa_painter { corner_painter };
    Gfx::IntRect corner_rect { { 0, 0 }, m_data.corner_bitmap_size };
    corner_aa_painter.fill_rect_with_rounded_corners(corner_rect, Color::NamedColor::Black,
        m_data.corner_radii.top_left, m_data.corner_radii.top_right, m_data.corner_radii.bottom_right, m_data.corner_radii.bottom_left);

    auto copy_page_masked = [&](auto const& mask_src, auto const& page_location) {
        for (int row = 0; row < mask_src.height(); ++row) {
            for (int col = 0; col < mask_src.width(); ++col) {
                auto corner_location = mask_src.location().translated(col, row);
                auto mask_pixel = m_corner_bitmap->get_pixel(corner_location);
                u8 mask_alpha = mask_pixel.alpha();
                if (m_corner_clip == CornerClip::Outside)
                    mask_alpha = ~mask_pixel.alpha();
                auto final_pixel = Color();
                if (mask_alpha > 0) {
                    auto page_pixel = page_painter.get_pixel(page_location.translated(col, row));
                    if (page_pixel.has_value())
                        final_pixel = page_pixel.value().with_alpha(mask_alpha);
                }
                m_corner_bitmap->set_pixel(corner_location, final_pixel);
            }
        }
    };

    // Copy the pixels under the corner mask (using the alpha of the mask):
    if (m_data.corner_radii.top_left)
        copy_page_masked(m_data.corner_radii.top_left.as_rect().translated(m_data.bitmap_locations.top_left), m_data.page_locations.top_left);
    if (m_data.corner_radii.top_right)
        copy_page_masked(m_data.corner_radii.top_right.as_rect().translated(m_data.bitmap_locations.top_right), m_data.page_locations.top_right);
    if (m_data.corner_radii.bottom_right)
        copy_page_masked(m_data.corner_radii.bottom_right.as_rect().translated(m_data.bitmap_locations.bottom_right), m_data.page_locations.bottom_right);
    if (m_data.corner_radii.bottom_left)
        copy_page_masked(m_data.corner_radii.bottom_left.as_rect().translated(m_data.bitmap_locations.bottom_left), m_data.page_locations.bottom_left);

    m_has_sampled = true;
}

void BorderRadiusCornerClipper::blit_corner_clipping(Gfx::Painter& painter)
{
    VERIFY(m_has_sampled);

    // Restore the corners:
    if (m_data.corner_radii.top_left)
        painter.blit(m_data.page_locations.top_left, *m_corner_bitmap, m_data.corner_radii.top_left.as_rect().translated(m_data.bitmap_locations.top_left));
    if (m_data.corner_radii.top_right)
        painter.blit(m_data.page_locations.top_right, *m_corner_bitmap, m_data.corner_radii.top_right.as_rect().translated(m_data.bitmap_locations.top_right));
    if (m_data.corner_radii.bottom_right)
        painter.blit(m_data.page_locations.bottom_right, *m_corner_bitmap, m_data.corner_radii.bottom_right.as_rect().translated(m_data.bitmap_locations.bottom_right));
    if (m_data.corner_radii.bottom_left)
        painter.blit(m_data.page_locations.bottom_left, *m_corner_bitmap, m_data.corner_radii.bottom_left.as_rect().translated(m_data.bitmap_locations.bottom_left));
}

}