ladybird/Userland/Libraries/LibWeb/Layout/SVGFormattingContext.cpp

/*
 * Copyright (c) 2021-2023, Andreas Kling <kling@serenityos.org>
 * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
 * Copyright (c) 2022, Tobias Christiansen <tobyase@serenityos.org>
 * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Debug.h>
#include <LibGfx/BoundingBox.h>
#include <LibGfx/Font/ScaledFont.h>
#include <LibGfx/TextLayout.h>
#include <LibWeb/Layout/BlockFormattingContext.h>
#include <LibWeb/Layout/SVGFormattingContext.h>
#include <LibWeb/Layout/SVGGeometryBox.h>
#include <LibWeb/Layout/SVGSVGBox.h>
#include <LibWeb/Layout/SVGTextBox.h>
#include <LibWeb/Layout/SVGTextPathBox.h>
#include <LibWeb/SVG/SVGForeignObjectElement.h>
#include <LibWeb/SVG/SVGGElement.h>
#include <LibWeb/SVG/SVGMaskElement.h>
#include <LibWeb/SVG/SVGSVGElement.h>
#include <LibWeb/SVG/SVGSymbolElement.h>
#include <LibWeb/SVG/SVGUseElement.h>

namespace Web::Layout {

SVGFormattingContext::SVGFormattingContext(LayoutState& state, Box const& box, FormattingContext* parent, Gfx::AffineTransform parent_viewbox_transform)
    : FormattingContext(Type::SVG, state, box, parent)
    , m_parent_viewbox_transform(parent_viewbox_transform)
{
}

SVGFormattingContext::~SVGFormattingContext() = default;

CSSPixels SVGFormattingContext::automatic_content_width() const
{
    return 0;
}

CSSPixels SVGFormattingContext::automatic_content_height() const
{
    return 0;
}

struct ViewBoxTransform {
    CSSPixelPoint offset;
    double scale_factor;
};

// https://svgwg.org/svg2-draft/coords.html#PreserveAspectRatioAttribute
static ViewBoxTransform scale_and_align_viewbox_content(SVG::PreserveAspectRatio const& preserve_aspect_ratio,
    SVG::ViewBox const& view_box, Gfx::FloatSize viewbox_scale, auto const& svg_box_state)
{
    ViewBoxTransform viewbox_transform {};

    switch (preserve_aspect_ratio.meet_or_slice) {
    case SVG::PreserveAspectRatio::MeetOrSlice::Meet:
        // meet (the default) - Scale the graphic such that:
        // - aspect ratio is preserved
        // - the entire ‘viewBox’ is visible within the SVG viewport
        // - the ‘viewBox’ is scaled up as much as possible, while still meeting the other criteria
        viewbox_transform.scale_factor = min(viewbox_scale.width(), viewbox_scale.height());
        break;
    case SVG::PreserveAspectRatio::MeetOrSlice::Slice:
        // slice - Scale the graphic such that:
        // aspect ratio is preserved
        // the entire SVG viewport is covered by the ‘viewBox’
        // the ‘viewBox’ is scaled down as much as possible, while still meeting the other criteria
        viewbox_transform.scale_factor = max(viewbox_scale.width(), viewbox_scale.height());
        break;
    default:
        VERIFY_NOT_REACHED();
    }

    // Handle X alignment:
    if (svg_box_state.has_definite_width()) {
        switch (preserve_aspect_ratio.align) {
        case SVG::PreserveAspectRatio::Align::xMinYMin:
        case SVG::PreserveAspectRatio::Align::xMinYMid:
        case SVG::PreserveAspectRatio::Align::xMinYMax:
            // Align the <min-x> of the element's ‘viewBox’ with the smallest X value of the SVG viewport.
            viewbox_transform.offset.translate_by(0, 0);
            break;
        case SVG::PreserveAspectRatio::Align::None: {
            // Do not force uniform scaling. Scale the graphic content of the given element non-uniformly
            // if necessary such that the element's bounding box exactly matches the SVG viewport rectangle.
            // FIXME: None is unimplemented (treat as xMidYMid)
            [[fallthrough]];
        }
        case SVG::PreserveAspectRatio::Align::xMidYMin:
        case SVG::PreserveAspectRatio::Align::xMidYMid:
        case SVG::PreserveAspectRatio::Align::xMidYMax:
            // Align the midpoint X value of the element's ‘viewBox’ with the midpoint X value of the SVG viewport.
            viewbox_transform.offset.translate_by((svg_box_state.content_width() - CSSPixels::nearest_value_for(view_box.width * viewbox_transform.scale_factor)) / 2, 0);
            break;
        case SVG::PreserveAspectRatio::Align::xMaxYMin:
        case SVG::PreserveAspectRatio::Align::xMaxYMid:
        case SVG::PreserveAspectRatio::Align::xMaxYMax:
            // Align the <min-x>+<width> of the element's ‘viewBox’ with the maximum X value of the SVG viewport.
            viewbox_transform.offset.translate_by((svg_box_state.content_width() - CSSPixels::nearest_value_for(view_box.width * viewbox_transform.scale_factor)), 0);
            break;
        default:
            VERIFY_NOT_REACHED();
        }
    }

    if (svg_box_state.has_definite_width()) {
        switch (preserve_aspect_ratio.align) {
        case SVG::PreserveAspectRatio::Align::xMinYMin:
        case SVG::PreserveAspectRatio::Align::xMidYMin:
        case SVG::PreserveAspectRatio::Align::xMaxYMin:
            // Align the <min-y> of the element's ‘viewBox’ with the smallest Y value of the SVG viewport.
            viewbox_transform.offset.translate_by(0, 0);
            break;
        case SVG::PreserveAspectRatio::Align::None: {
            // Do not force uniform scaling. Scale the graphic content of the given element non-uniformly
            // if necessary such that the element's bounding box exactly matches the SVG viewport rectangle.
            // FIXME: None is unimplemented (treat as xMidYMid)
            [[fallthrough]];
        }
        case SVG::PreserveAspectRatio::Align::xMinYMid:
        case SVG::PreserveAspectRatio::Align::xMidYMid:
        case SVG::PreserveAspectRatio::Align::xMaxYMid:
            // Align the midpoint Y value of the element's ‘viewBox’ with the midpoint Y value of the SVG viewport.
            viewbox_transform.offset.translate_by(0, (svg_box_state.content_height() - CSSPixels::nearest_value_for(view_box.height * viewbox_transform.scale_factor)) / 2);
            break;
        case SVG::PreserveAspectRatio::Align::xMinYMax:
        case SVG::PreserveAspectRatio::Align::xMidYMax:
        case SVG::PreserveAspectRatio::Align::xMaxYMax:
            // Align the <min-y>+<height> of the element's ‘viewBox’ with the maximum Y value of the SVG viewport.
            viewbox_transform.offset.translate_by(0, (svg_box_state.content_height() - CSSPixels::nearest_value_for(view_box.height * viewbox_transform.scale_factor)));
            break;
        default:
            VERIFY_NOT_REACHED();
        }
    }

    return viewbox_transform;
}

static bool is_container_element(Node const& node)
{
    // https://svgwg.org/svg2-draft/struct.html#GroupsOverview
    auto* dom_node = node.dom_node();
    if (!dom_node)
        return false;
    if (is<SVG::SVGUseElement>(dom_node))
        return true;
    if (is<SVG::SVGSymbolElement>(dom_node))
        return true;
    if (is<SVG::SVGGElement>(dom_node))
        return true;
    if (is<SVG::SVGMaskElement>(dom_node))
        return true;
    return false;
}

enum class TraversalDecision {
    Continue,
    SkipChildrenAndContinue,
    Break,
};

// FIXME: Add TraversalDecision::SkipChildrenAndContinue to TreeNode's implementation.
template<typename Callback>
static TraversalDecision for_each_in_inclusive_subtree(Layout::Node const& node, Callback callback)
{
    if (auto decision = callback(node); decision != TraversalDecision::Continue)
        return decision;
    for (auto* child = node.first_child(); child; child = child->next_sibling()) {
        if (for_each_in_inclusive_subtree(*child, callback) == TraversalDecision::Break)
            return TraversalDecision::Break;
    }
    return TraversalDecision::Continue;
}

// FIXME: Add TraversalDecision::SkipChildrenAndContinue to TreeNode's implementation.
template<typename Callback>
static TraversalDecision for_each_in_subtree(Layout::Node const& node, Callback callback)
{
    for (auto* child = node.first_child(); child; child = child->next_sibling()) {
        if (for_each_in_inclusive_subtree(*child, callback) == TraversalDecision::Break)
            return TraversalDecision::Break;
    }
    return TraversalDecision::Continue;
}

void SVGFormattingContext::run(Box const& box, LayoutMode layout_mode, AvailableSpace const& available_space)
{
    // NOTE: SVG doesn't have a "formatting context" in the spec, but this is the most
    //       obvious way to drive SVG layout in our engine at the moment.

    auto& svg_viewport = dynamic_cast<SVG::SVGViewport const&>(*box.dom_node());
    auto& svg_box_state = m_state.get_mutable(box);

    // NOTE: We consider all SVG root elements to have definite size in both axes.
    //       I'm not sure if this is good or bad, but our viewport transform logic depends on it.
    svg_box_state.set_has_definite_width(true);
    svg_box_state.set_has_definite_height(true);

    auto viewbox = svg_viewport.view_box();
    // https://svgwg.org/svg2-draft/coords.html#ViewBoxAttribute
    if (viewbox.has_value()) {
        if (viewbox->width < 0 || viewbox->height < 0) {
            // A negative value for <width> or <height> is an error and invalidates the ‘viewBox’ attribute.
            viewbox = {};
        } else if (viewbox->width == 0 || viewbox->height == 0) {
            // A value of zero disables rendering of the element.
            return;
        }
    }

    auto viewbox_transform = [&] {
        if (!viewbox.has_value())
            return m_parent_viewbox_transform;

        // FIXME: This should allow just one of width or height to be specified.
        // E.g. We should be able to layout <svg width="100%"> where height is unspecified/auto.
        if (!svg_box_state.has_definite_width() || !svg_box_state.has_definite_height()) {
            dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Attempting to layout indefinitely sized SVG with a viewbox -- this likely won't work!");
        }

        auto scale_width = svg_box_state.has_definite_width() ? svg_box_state.content_width() / viewbox->width : 1;
        auto scale_height = svg_box_state.has_definite_height() ? svg_box_state.content_height() / viewbox->height : 1;

        // The initial value for preserveAspectRatio is xMidYMid meet.
        auto preserve_aspect_ratio = svg_viewport.preserve_aspect_ratio().value_or(SVG::PreserveAspectRatio {});
        auto viewbox_offset_and_scale = scale_and_align_viewbox_content(preserve_aspect_ratio, *viewbox, { scale_width, scale_height }, svg_box_state);

        CSSPixelPoint offset = viewbox_offset_and_scale.offset;
        return Gfx::AffineTransform { m_parent_viewbox_transform }.multiply(Gfx::AffineTransform {}
                                                                                .translate(offset.to_type<float>())
                                                                                .scale(viewbox_offset_and_scale.scale_factor, viewbox_offset_and_scale.scale_factor)
                                                                                .translate({ -viewbox->min_x, -viewbox->min_y }));
    }();

    if (svg_box_state.has_definite_width() && svg_box_state.has_definite_height()) {
        // Scale the box of the viewport based on the parent's viewBox transform.
        // The viewBox transform is always just a simple scale + offset.
        // FIXME: Avoid converting SVG box to floats.
        Gfx::FloatRect svg_rect = { svg_box_state.offset.to_type<float>(),
            { float(svg_box_state.content_width()), float(svg_box_state.content_height()) } };
        svg_rect = m_parent_viewbox_transform.map(svg_rect);
        svg_box_state.set_content_offset(svg_rect.location().to_type<CSSPixels>());
        svg_box_state.set_content_width(CSSPixels(svg_rect.width()));
        svg_box_state.set_content_height(CSSPixels(svg_rect.height()));
        svg_box_state.set_has_definite_width(true);
        svg_box_state.set_has_definite_height(true);
    }

    auto root_offset = svg_box_state.offset;
    box.for_each_child_of_type<BlockContainer>([&](BlockContainer const& child_box) {
        if (is<SVG::SVGForeignObjectElement>(child_box.dom_node())) {
            Layout::BlockFormattingContext bfc(m_state, child_box, this);
            bfc.run(child_box, LayoutMode::Normal, available_space);

            auto& child_state = m_state.get_mutable(child_box);
            child_state.set_content_offset(child_state.offset.translated(root_offset));
        }
        return IterationDecision::Continue;
    });

    auto viewport_width = [&] {
        if (viewbox.has_value())
            return CSSPixels::nearest_value_for(viewbox->width);
        if (svg_box_state.has_definite_width())
            return svg_box_state.content_width();
        dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Failed to resolve width of SVG viewport!");
        return CSSPixels {};
    }();

    auto viewport_height = [&] {
        if (viewbox.has_value())
            return CSSPixels::nearest_value_for(viewbox->height);
        if (svg_box_state.has_definite_height())
            return svg_box_state.content_height();
        dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Failed to resolve height of SVG viewport!");
        return CSSPixels {};
    }();

    for_each_in_subtree(box, [&](Node const& descendant) {
        if (is<SVG::SVGViewport>(descendant.dom_node())) {
            // Layout for a nested SVG viewport.
            // https://svgwg.org/svg2-draft/coords.html#EstablishingANewSVGViewport.
            SVGFormattingContext nested_context(m_state, static_cast<Box const&>(descendant), this, viewbox_transform);
            auto& nested_viewport_state = m_state.get_mutable(static_cast<Box const&>(descendant));
            auto resolve_dimension = [](auto& node, auto size, auto reference_value) {
                // The value auto for width and height on the ‘svg’ element is treated as 100%.
                // https://svgwg.org/svg2-draft/geometry.html#Sizing
                if (size.is_auto())
                    return reference_value;
                return size.to_px(node, reference_value);
            };

            auto nested_viewport_x = descendant.computed_values().x().to_px(descendant, viewport_width);
            auto nested_viewport_y = descendant.computed_values().y().to_px(descendant, viewport_height);
            auto nested_viewport_width = resolve_dimension(descendant, descendant.computed_values().width(), viewport_width);
            auto nested_viewport_height = resolve_dimension(descendant, descendant.computed_values().height(), viewport_height);
            nested_viewport_state.set_content_offset({ nested_viewport_x, nested_viewport_y });
            nested_viewport_state.set_content_width(nested_viewport_width);
            nested_viewport_state.set_content_height(nested_viewport_height);
            nested_viewport_state.set_has_definite_width(true);
            nested_viewport_state.set_has_definite_height(true);
            nested_context.run(static_cast<Box const&>(descendant), layout_mode, available_space);
            return TraversalDecision::SkipChildrenAndContinue;
        }
        if (is<SVGGraphicsBox>(descendant)) {
            auto const& graphics_box = static_cast<SVGGraphicsBox const&>(descendant);
            auto& dom_node = const_cast<SVGGraphicsBox&>(graphics_box).dom_node();
            auto& graphics_box_state = m_state.get_mutable(graphics_box);

            auto svg_transform = dom_node.get_transform();
            graphics_box_state.set_computed_svg_transforms(Painting::SVGGraphicsPaintable::ComputedTransforms(viewbox_transform, svg_transform));
            auto to_css_pixels_transform = Gfx::AffineTransform {}.multiply(viewbox_transform).multiply(svg_transform);

            Gfx::Path path;
            if (is<SVGGeometryBox>(descendant)) {
                path = static_cast<SVG::SVGGeometryElement&>(dom_node).get_path({ viewport_width, viewport_height });
            } else if (is<SVGTextBox>(descendant)) {
                auto& text_element = static_cast<SVG::SVGTextPositioningElement&>(dom_node);

                auto& font = graphics_box.first_available_font();
                auto text_contents = text_element.text_contents();
                Utf8View text_utf8 { text_contents };
                auto text_width = font.width(text_utf8);

                auto text_offset = text_element.get_offset();
                // https://svgwg.org/svg2-draft/text.html#TextAnchoringProperties
                switch (text_element.text_anchor().value_or(SVG::TextAnchor::Start)) {
                case SVG::TextAnchor::Start:
                    // The rendered characters are aligned such that the start of the resulting rendered text is at the initial
                    // current text position.
                    break;
                case SVG::TextAnchor::Middle: {
                    // The rendered characters are shifted such that the geometric middle of the resulting rendered text
                    // (determined from the initial and final current text position before applying the text-anchor property)
                    // is at the initial current text position.
                    text_offset.translate_by(-text_width / 2, 0);
                    break;
                }
                case SVG::TextAnchor::End: {
                    // The rendered characters are shifted such that the end of the resulting rendered text (final current text
                    // position before applying the text-anchor property) is at the initial current text position.
                    text_offset.translate_by(-text_width, 0);
                    break;
                }
                default:
                    VERIFY_NOT_REACHED();
                }

                path.move_to(text_offset);
                path.text(text_utf8, font);
            } else if (is<SVGTextPathBox>(descendant)) {
                auto& text_path_element = static_cast<SVG::SVGTextPathElement&>(dom_node);
                auto path_or_shape = text_path_element.path_or_shape();
                if (!path_or_shape)
                    return TraversalDecision::Continue;

                auto& font = graphics_box.first_available_font();
                auto text_contents = text_path_element.text_contents();
                Utf8View text_utf8 { text_contents };

                auto shape_path = const_cast<SVG::SVGGeometryElement&>(*path_or_shape).get_path({ viewport_width, viewport_height });
                path = shape_path.place_text_along(text_utf8, font);
            }

            auto path_bounding_box = to_css_pixels_transform.map(path.bounding_box()).to_type<CSSPixels>();
            // Stroke increases the path's size by stroke_width/2 per side.
            CSSPixels stroke_width = CSSPixels::nearest_value_for(graphics_box.dom_node().visible_stroke_width() * viewbox_transform.x_scale());
            path_bounding_box.inflate(stroke_width, stroke_width);
            graphics_box_state.set_content_offset(path_bounding_box.top_left());
            graphics_box_state.set_content_width(path_bounding_box.width());
            graphics_box_state.set_content_height(path_bounding_box.height());
            graphics_box_state.set_has_definite_width(true);
            graphics_box_state.set_has_definite_height(true);
            graphics_box_state.set_computed_svg_path(move(path));
        }
        return TraversalDecision::Continue;
    });

    // https://svgwg.org/svg2-draft/struct.html#Groups
    // 5.2. Grouping: the ‘g’ element
    // The ‘g’ element is a container element for grouping together related graphics elements.
    box.for_each_in_subtree_of_type<Box>([&](Box const& descendant) {
        if (is_container_element(descendant)) {
            Gfx::BoundingBox<CSSPixels> bounding_box;
            descendant.for_each_in_subtree_of_type<Box>([&](Box const& child_of_svg_container) {
                auto& box_state = m_state.get(child_of_svg_container);
                bounding_box.add_point(box_state.offset);
                bounding_box.add_point(box_state.offset.translated(box_state.content_width(), box_state.content_height()));
                return IterationDecision::Continue;
            });

            auto& box_state = m_state.get_mutable(descendant);
            box_state.set_content_x(bounding_box.x());
            box_state.set_content_y(bounding_box.y());
            box_state.set_content_width(bounding_box.width());
            box_state.set_content_height(bounding_box.height());
            box_state.set_has_definite_width(true);
            box_state.set_has_definite_height(true);
        }
        return IterationDecision::Continue;
    });
}

}