ladybird/Libraries/LibWeb/Layout/SVGFormattingContext.cpp

/*
 * Copyright (c) 2021-2023, Andreas Kling <andreas@ladybird.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/Path.h>
#include <LibGfx/TextLayout.h>
#include <LibWeb/Layout/BlockFormattingContext.h>
#include <LibWeb/Layout/SVGClipBox.h>
#include <LibWeb/Layout/SVGFormattingContext.h>
#include <LibWeb/Layout/SVGGeometryBox.h>
#include <LibWeb/Layout/SVGImageBox.h>
#include <LibWeb/Layout/SVGMaskBox.h>
#include <LibWeb/Layout/Viewport.h>
#include <LibWeb/SVG/SVGAElement.h>
#include <LibWeb/SVG/SVGClipPathElement.h>
#include <LibWeb/SVG/SVGForeignObjectElement.h>
#include <LibWeb/SVG/SVGGElement.h>
#include <LibWeb/SVG/SVGImageElement.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, LayoutMode layout_mode, Box const& box, FormattingContext* parent, Gfx::AffineTransform parent_viewbox_transform)
    : FormattingContext(Type::SVG, layout_mode, 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_x;
    double scale_factor_y;
};

// 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 {};

    if (preserve_aspect_ratio.align == SVG::PreserveAspectRatio::Align::None) {
        viewbox_transform.scale_factor_x = viewbox_scale.width();
        viewbox_transform.scale_factor_y = viewbox_scale.height();
        viewbox_transform.offset = {};
        return 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_x = viewbox_transform.scale_factor_y = 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_x = viewbox_transform.scale_factor_y = 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_x)) / 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_x)), 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_y)) / 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_y)));
            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::SVGAElement>(dom_node))
        return true;
    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;
}

void SVGFormattingContext::run(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&>(*context_box().dom_node());
    auto& svg_box_state = m_state.get_mutable(context_box());

    if (!this->context_box().root().document().is_decoded_svg()) {
        // Overwrite the content width/height with the styled node width/height (from <svg width height ...>)

        // NOTE: If a height had not been provided by the svg element, it was set to the height of the container
        //       (see BlockFormattingContext::layout_viewport)
        if (svg_box_state.node().computed_values().width().is_length())
            svg_box_state.set_content_width(svg_box_state.node().computed_values().width().length().to_px(svg_box_state.node()));
        if (svg_box_state.node().computed_values().height().is_length())
            svg_box_state.set_content_height(svg_box_state.node().computed_values().height().length().to_px(svg_box_state.node()));
        // FIXME: In SVG 2, length can also be a percentage. We'll need to support that.
    }

    // 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;
        }
    }

    m_current_viewbox_transform = m_parent_viewbox_transform;
    if (viewbox.has_value()) {
        // 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;
        m_current_viewbox_transform = Gfx::AffineTransform { m_current_viewbox_transform }.multiply(Gfx::AffineTransform {}
                .translate(offset.to_type<float>())
                .scale(viewbox_offset_and_scale.scale_factor_x, viewbox_offset_and_scale.scale_factor_y)
                .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 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 {};
    }();

    m_available_space = available_space;
    m_svg_offset = svg_box_state.offset;
    m_viewport_size = { viewport_width, viewport_height };

    context_box().for_each_child_of_type<Box>([&](Box const& child) {
        layout_svg_element(child);
        return IterationDecision::Continue;
    });
}

void SVGFormattingContext::layout_svg_element(Box const& child)
{
    if (is<SVG::SVGViewport>(child.dom_node())) {
        layout_nested_viewport(child);
    } else if (is<SVG::SVGForeignObjectElement>(child.dom_node()) && is<BlockContainer>(child)) {
        Layout::BlockFormattingContext bfc(m_state, m_layout_mode, static_cast<BlockContainer const&>(child), this);
        bfc.run(*m_available_space);
        auto& child_state = m_state.get_mutable(child);
        child_state.set_content_offset(child_state.offset.translated(m_svg_offset));
        child.for_each_child_of_type<SVGMaskBox>([&](SVGMaskBox const& child) {
            layout_svg_element(child);
            return IterationDecision::Continue;
        });
    } else if (is<SVGGraphicsBox>(child)) {
        layout_graphics_element(static_cast<SVGGraphicsBox const&>(child));
    }
}

void SVGFormattingContext::layout_nested_viewport(Box const& viewport)
{
    // Layout for a nested SVG viewport.
    // https://svgwg.org/svg2-draft/coords.html#EstablishingANewSVGViewport.
    SVGFormattingContext nested_context(m_state, m_layout_mode, viewport, this, m_current_viewbox_transform);
    auto& nested_viewport_state = m_state.get_mutable(viewport);
    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 = viewport.computed_values().x().to_px(viewport, m_viewport_size.width());
    auto nested_viewport_y = viewport.computed_values().y().to_px(viewport, m_viewport_size.height());
    auto nested_viewport_width = resolve_dimension(viewport, viewport.computed_values().width(), m_viewport_size.width());
    auto nested_viewport_height = resolve_dimension(viewport, viewport.computed_values().height(), m_viewport_size.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(*m_available_space);
}

Gfx::Path SVGFormattingContext::compute_path_for_text(SVGTextBox const& text_box)
{
    auto& text_element = static_cast<SVG::SVGTextPositioningElement const&>(text_box.dom_node());
    // FIXME: Use per-code-point fonts.
    auto& font = text_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(m_viewport_size);

    // 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();
    }

    Gfx::Path path;
    path.move_to(text_offset);
    path.text(text_utf8, font);
    return path;
}

Gfx::Path SVGFormattingContext::compute_path_for_text_path(SVGTextPathBox const& text_path_box)
{
    auto& text_path_element = static_cast<SVG::SVGTextPathElement const&>(text_path_box.dom_node());
    auto path_or_shape = text_path_element.path_or_shape();
    if (!path_or_shape)
        return {};

    // FIXME: Use per-code-point fonts.
    auto& font = text_path_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(m_viewport_size);
    return shape_path.place_text_along(text_utf8, font);
}

void SVGFormattingContext::layout_path_like_element(SVGGraphicsBox const& graphics_box)
{
    auto& graphics_box_state = m_state.get_mutable(graphics_box);
    VERIFY(graphics_box_state.computed_svg_transforms().has_value());

    auto to_css_pixels_transform = Gfx::AffineTransform {}
                                       .multiply(m_current_viewbox_transform)
                                       .multiply(graphics_box_state.computed_svg_transforms()->svg_transform());

    Gfx::Path path;
    if (is<SVGGeometryBox>(graphics_box)) {
        auto& geometry_box = static_cast<SVGGeometryBox const&>(graphics_box);
        path = const_cast<SVGGeometryBox&>(geometry_box).dom_node().get_path(m_viewport_size);
    } else if (is<SVGTextBox>(graphics_box)) {
        auto& text_box = static_cast<SVGTextBox const&>(graphics_box);
        path = compute_path_for_text(text_box);
        // <text> and <tspan> elements can contain more text elements.
        text_box.for_each_child_of_type<SVGGraphicsBox>([&](auto& child) {
            if (is<SVGTextBox>(child) || is<SVGTextPathBox>(child))
                layout_graphics_element(child);
            return IterationDecision::Continue;
        });
    } else if (is<SVGTextPathBox>(graphics_box)) {
        // FIXME: Support <tspan> in <textPath>.
        path = compute_path_for_text_path(static_cast<SVGTextPathBox const&>(graphics_box));
    }

    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() * m_current_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));
}

void SVGFormattingContext::layout_graphics_element(SVGGraphicsBox const& graphics_box)
{
    auto& graphics_box_state = m_state.get_mutable(graphics_box);
    auto svg_transform = const_cast<SVGGraphicsBox&>(graphics_box).dom_node().get_transform();
    graphics_box_state.set_computed_svg_transforms(Painting::SVGGraphicsPaintable::ComputedTransforms(m_current_viewbox_transform, svg_transform));

    if (is_container_element(graphics_box)) {
        // 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.
        layout_container_element(graphics_box);
    } else if (is<SVGImageBox>(graphics_box)) {
        layout_image_element(static_cast<SVGImageBox const&>(graphics_box));
    } else {
        // Assume this is a path-like element.
        layout_path_like_element(graphics_box);
    }

    if (auto* mask_box = graphics_box.first_child_of_type<SVGMaskBox>())
        layout_mask_or_clip(*mask_box);

    if (auto* clip_box = graphics_box.first_child_of_type<SVGClipBox>())
        layout_mask_or_clip(*clip_box);
}

void SVGFormattingContext::layout_image_element(SVGImageBox const& image_box)
{
    auto& box_state = m_state.get_mutable(image_box);
    auto bounding_box = image_box.dom_node().bounding_box();
    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);
}

void SVGFormattingContext::layout_mask_or_clip(SVGBox const& mask_or_clip)
{
    SVG::SVGUnits content_units {};
    if (is<SVGMaskBox>(mask_or_clip))
        content_units = static_cast<SVGMaskBox const&>(mask_or_clip).dom_node().mask_content_units();
    else if (is<SVGClipBox>(mask_or_clip))
        content_units = static_cast<SVGClipBox const&>(mask_or_clip).dom_node().clip_path_units();
    else
        VERIFY_NOT_REACHED();
    // FIXME: Somehow limit <clipPath> contents to: shape elements, <text>, and <use>.
    auto& layout_state = m_state.get_mutable(mask_or_clip);
    auto parent_viewbox_transform = m_current_viewbox_transform;
    if (content_units == SVG::SVGUnits::ObjectBoundingBox) {
        auto* parent_node = mask_or_clip.parent();
        auto& parent_node_state = m_state.get(*parent_node);
        layout_state.set_content_width(parent_node_state.content_width());
        layout_state.set_content_height(parent_node_state.content_height());
        parent_viewbox_transform = Gfx::AffineTransform {}.translate(parent_node_state.offset.to_type<float>());
    } else {
        layout_state.set_content_width(m_viewport_size.width());
        layout_state.set_content_height(m_viewport_size.height());
    }
    // Pretend masks/clips are a viewport so we can scale the contents depending on the `contentUnits`.
    SVGFormattingContext nested_context(m_state, m_layout_mode, mask_or_clip, this, parent_viewbox_transform);
    layout_state.set_has_definite_width(true);
    layout_state.set_has_definite_height(true);
    nested_context.run(*m_available_space);
}

void SVGFormattingContext::layout_container_element(SVGBox const& container)
{
    auto& box_state = m_state.get_mutable(container);
    Gfx::BoundingBox<CSSPixels> bounding_box;
    container.for_each_child_of_type<Box>([&](Box const& child) {
        // Masks/clips do not change the bounding box of their parents.
        if (is<SVGMaskBox>(child) || is<SVGClipBox>(child))
            return IterationDecision::Continue;
        layout_svg_element(child);
        auto& child_state = m_state.get(child);
        bounding_box.add_point(child_state.offset);
        bounding_box.add_point(child_state.offset.translated(child_state.content_width(), child_state.content_height()));
        return IterationDecision::Continue;
    });
    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);
}

}