LibWeb: Implement the `<use>` SVG element

The SVG <use> element is used to be able to reuse other SVG graphics
without having to re-write the svg element.

We now support this feature! :^)

10 files changed, 323 insertions, 1 deletions

diff --git a/Userland/Libraries/LibWeb/CMakeLists.txt b/Userland/Libraries/LibWeb/CMakeLists.txt
index 4439811ef8..0e79a2caa9 100644
--- a/Userland/Libraries/LibWeb/CMakeLists.txt
+++ b/Userland/Libraries/LibWeb/CMakeLists.txt
@@ -523,6 +523,7 @@ set(SOURCES
     SVG/SVGSVGElement.cpp
     SVG/SVGStopElement.cpp
     SVG/SVGTextContentElement.cpp
+    SVG/SVGUseElement.cpp
     SVG/TagNames.cpp
     SVG/ViewBox.cpp
     Selection/Selection.cpp
diff --git a/Userland/Libraries/LibWeb/DOM/ElementFactory.cpp b/Userland/Libraries/LibWeb/DOM/ElementFactory.cpp
index 10867906ae..00e2802f9c 100644
--- a/Userland/Libraries/LibWeb/DOM/ElementFactory.cpp
+++ b/Userland/Libraries/LibWeb/DOM/ElementFactory.cpp
@@ -98,6 +98,7 @@
 #include <LibWeb/SVG/SVGSVGElement.h>
 #include <LibWeb/SVG/SVGStopElement.h>
 #include <LibWeb/SVG/SVGTextContentElement.h>
+#include <LibWeb/SVG/SVGUseElement.h>
 #include <LibWeb/SVG/TagNames.h>
 #include <LibWeb/WebIDL/AbstractOperations.h>
 
@@ -455,6 +456,8 @@ static WebIDL::ExceptionOr<JS::GCPtr<SVG::SVGElement>> create_svg_element(JS::Re
         return MUST_OR_THROW_OOM(realm.heap().allocate<SVG::SVGStopElement>(realm, document, move(qualified_name)));
     if (local_name == SVG::TagNames::text)
         return MUST_OR_THROW_OOM(realm.heap().allocate<SVG::SVGTextContentElement>(realm, document, move(qualified_name)));
+    if (local_name == SVG::TagNames::use)
+        return MUST_OR_THROW_OOM(realm.heap().allocate<SVG::SVGUseElement>(realm, document, move(qualified_name)));
 
     return nullptr;
 }
diff --git a/Userland/Libraries/LibWeb/SVG/AttributeNames.h b/Userland/Libraries/LibWeb/SVG/AttributeNames.h
index 96413616e1..7594e138b3 100644
--- a/Userland/Libraries/LibWeb/SVG/AttributeNames.h
+++ b/Userland/Libraries/LibWeb/SVG/AttributeNames.h
@@ -32,6 +32,7 @@ namespace Web::SVG::AttributeNames {
     E(gradientTransform)            \
     E(gradientUnits)                \
     E(height)                       \
+    E(href)                         \
     E(kernelMatrix)                 \
     E(kernelUnitLength)             \
     E(keyPoints)                    \
diff --git a/Userland/Libraries/LibWeb/SVG/SVGElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGElement.cpp
index 09da38721d..a09e81c0af 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGElement.cpp
+++ b/Userland/Libraries/LibWeb/SVG/SVGElement.cpp
@@ -1,13 +1,16 @@
 /*
  * Copyright (c) 2020, Matthew Olsson <mattco@serenityos.org>
+ * Copyright (c) 2023, Preston Taylor <95388976+PrestonLTaylor@users.noreply.github.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #include <LibWeb/Bindings/ExceptionOrUtils.h>
 #include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/DOM/Document.h>
 #include <LibWeb/HTML/DOMStringMap.h>
 #include <LibWeb/SVG/SVGElement.h>
+#include <LibWeb/SVG/SVGUseElement.h>
 
 namespace Web::SVG {
 
@@ -34,4 +37,56 @@ void SVGElement::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_dataset);
 }
 
+void SVGElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
+{
+    Base::parse_attribute(name, value);
+
+    update_use_elements_that_reference_this();
+}
+
+void SVGElement::inserted()
+{
+    Base::inserted();
+
+    update_use_elements_that_reference_this();
+}
+
+void SVGElement::children_changed()
+{
+    Base::children_changed();
+
+    update_use_elements_that_reference_this();
+}
+
+void SVGElement::update_use_elements_that_reference_this()
+{
+    if (is<SVGUseElement>(this)) {
+        return;
+    }
+
+    document().for_each_in_subtree_of_type<SVGUseElement>([this](SVGUseElement& use_element) {
+        use_element.svg_element_changed(*this);
+        return IterationDecision::Continue;
+    });
+}
+
+void SVGElement::removed_from(Node* parent)
+{
+    Base::removed_from(parent);
+
+    remove_from_use_element_that_reference_this();
+}
+
+void SVGElement::remove_from_use_element_that_reference_this()
+{
+    if (is<SVGUseElement>(this)) {
+        return;
+    }
+
+    document().for_each_in_subtree_of_type<SVGUseElement>([this](SVGUseElement& use_element) {
+        use_element.svg_element_removed(*this);
+        return IterationDecision::Continue;
+    });
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/SVG/SVGElement.h b/Userland/Libraries/LibWeb/SVG/SVGElement.h
index 1329d86814..93fd507634 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGElement.h
+++ b/Userland/Libraries/LibWeb/SVG/SVGElement.h
@@ -16,6 +16,12 @@ class SVGElement : public DOM::Element {
 public:
     virtual bool requires_svg_container() const override { return true; }
 
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
+
+    virtual void children_changed() override;
+    virtual void inserted() override;
+    virtual void removed_from(Node*) override;
+
     HTML::DOMStringMap* dataset() { return m_dataset.ptr(); }
     HTML::DOMStringMap const* dataset() const { return m_dataset.ptr(); }
 
@@ -25,6 +31,9 @@ protected:
     virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
+    void update_use_elements_that_reference_this();
+    void remove_from_use_element_that_reference_this();
+
     JS::GCPtr<HTML::DOMStringMap> m_dataset;
 
 private:
diff --git a/Userland/Libraries/LibWeb/SVG/SVGUseElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGUseElement.cpp
new file mode 100644
index 0000000000..fcad33e765
--- /dev/null
+++ b/Userland/Libraries/LibWeb/SVG/SVGUseElement.cpp
@@ -0,0 +1,177 @@
+/*
+ * Copyright (c) 2023, Preston Taylor <95388976+PrestonLTaylor@users.noreply.github.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/DOM/Document.h>
+#include <LibWeb/DOM/ElementFactory.h>
+#include <LibWeb/DOM/Event.h>
+#include <LibWeb/DOM/ShadowRoot.h>
+#include <LibWeb/Namespace.h>
+#include <LibWeb/SVG/AttributeNames.h>
+#include <LibWeb/SVG/SVGSVGElement.h>
+#include <LibWeb/SVG/SVGUseElement.h>
+
+namespace Web::SVG {
+
+SVGUseElement::SVGUseElement(DOM::Document& document, DOM::QualifiedName qualified_name)
+    : SVGGraphicsElement(document, qualified_name)
+{
+}
+
+JS::ThrowCompletionOr<void> SVGUseElement::initialize(JS::Realm& realm)
+{
+    MUST_OR_THROW_OOM(Base::initialize(realm));
+    set_prototype(&Bindings::ensure_web_prototype<Bindings::SVGUseElementPrototype>(realm, "SVGUseElement"));
+
+    // The shadow tree is open (inspectable by script), but read-only.
+    auto shadow_root = TRY(heap().allocate<DOM::ShadowRoot>(realm, document(), *this, Bindings::ShadowRootMode::Open));
+
+    // The user agent must create a use-element shadow tree whose host is the ‘use’ element itself
+    set_shadow_root(shadow_root);
+
+    m_document_observer = TRY(realm.heap().allocate<DOM::DocumentObserver>(realm, realm, document()));
+    m_document_observer->document_fully_loaded = [this]() {
+        clone_element_tree_as_our_shadow_tree(referenced_element());
+    };
+
+    return {};
+}
+
+void SVGUseElement::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(m_document_observer);
+}
+
+void SVGUseElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
+{
+    Base::parse_attribute(name, value);
+
+    // https://svgwg.org/svg2-draft/struct.html#UseLayout
+    if (name == SVG::AttributeNames::x) {
+        m_x = AttributeParser::parse_coordinate(value);
+    } else if (name == SVG::AttributeNames::y) {
+        m_y = AttributeParser::parse_coordinate(value);
+    } else if (name == SVG::AttributeNames::href) {
+        // FIXME: Support the xlink:href attribute as a fallback
+        m_referenced_id = parse_id_from_href(value);
+    }
+}
+
+Optional<StringView> SVGUseElement::parse_id_from_href(DeprecatedString const& href)
+{
+    auto id_seperator = href.find('#');
+    if (!id_seperator.has_value()) {
+        return {};
+    }
+
+    return href.substring_view(id_seperator.value() + 1);
+}
+
+void SVGUseElement::inserted()
+{
+    Base::inserted();
+
+    // The x and y properties define an additional transformation (translate(x,y), where x and y represent the computed value of the corresponding property)
+    // to be applied to the ‘use’ element, after any transformations specified with other properties
+    m_transform.translate(m_x.value_or(0), m_y.value_or(0));
+}
+
+void SVGUseElement::svg_element_changed(SVGElement& svg_element)
+{
+    auto to_clone = referenced_element();
+    if (!to_clone) {
+        return;
+    }
+
+    // NOTE: We need to check the ancestor because parse_attribute of a child doesn't call children_changed on the parent(s)
+    if (to_clone == &svg_element || to_clone->is_ancestor_of(svg_element)) {
+        clone_element_tree_as_our_shadow_tree(to_clone);
+    }
+}
+
+void SVGUseElement::svg_element_removed(SVGElement& svg_element)
+{
+    if (!m_referenced_id.has_value()) {
+        return;
+    }
+
+    if (svg_element.attribute("id"sv).matches(m_referenced_id.value())) {
+        shadow_root()->remove_all_children();
+    }
+}
+
+JS::GCPtr<DOM::Element> SVGUseElement::referenced_element()
+{
+    if (!m_referenced_id.has_value()) {
+        return nullptr;
+    }
+
+    // FIXME: Support loading of external svg documents
+    return document().get_element_by_id(m_referenced_id.value());
+}
+
+// https://svgwg.org/svg2-draft/struct.html#UseShadowTree
+void SVGUseElement::clone_element_tree_as_our_shadow_tree(Element* to_clone) const
+{
+    shadow_root()->remove_all_children();
+
+    if (to_clone && is_valid_reference_element(to_clone)) {
+        // The ‘use’ element references another element, a copy of which is rendered in place of the ‘use’ in the document.
+        auto cloned_reference_node = to_clone->clone_node(nullptr, true);
+        shadow_root()->append_child(cloned_reference_node).release_value_but_fixme_should_propagate_errors();
+    }
+}
+
+bool SVGUseElement::is_valid_reference_element(Element* reference_element) const
+{
+    // If the referenced element that results from resolving the URL is not an SVG element, then the reference is invalid and the ‘use’ element is in error.
+    // If the referenced element is a (shadow-including) ancestor of the ‘use’ element, then this is an invalid circular reference and the ‘use’ element is in error.
+    return reference_element->is_svg_element() && !reference_element->is_ancestor_of(*this);
+}
+
+// https://www.w3.org/TR/SVG11/shapes.html#RectElementXAttribute
+JS::NonnullGCPtr<SVGAnimatedLength> SVGUseElement::x() const
+{
+    // FIXME: Populate the unit type when it is parsed (0 here is "unknown").
+    // FIXME: Create a proper animated value when animations are supported.
+    auto base_length = SVGLength::create(realm(), 0, m_x.value_or(0)).release_value_but_fixme_should_propagate_errors();
+    auto anim_length = SVGLength::create(realm(), 0, m_x.value_or(0)).release_value_but_fixme_should_propagate_errors();
+    return SVGAnimatedLength::create(realm(), move(base_length), move(anim_length)).release_value_but_fixme_should_propagate_errors();
+}
+
+// https://www.w3.org/TR/SVG11/shapes.html#RectElementYAttribute
+JS::NonnullGCPtr<SVGAnimatedLength> SVGUseElement::y() const
+{
+    // FIXME: Populate the unit type when it is parsed (0 here is "unknown").
+    // FIXME: Create a proper animated value when animations are supported.
+    auto base_length = SVGLength::create(realm(), 0, m_y.value_or(0)).release_value_but_fixme_should_propagate_errors();
+    auto anim_length = SVGLength::create(realm(), 0, m_y.value_or(0)).release_value_but_fixme_should_propagate_errors();
+    return SVGAnimatedLength::create(realm(), move(base_length), move(anim_length)).release_value_but_fixme_should_propagate_errors();
+}
+
+JS::NonnullGCPtr<SVGAnimatedLength> SVGUseElement::width() const
+{
+    TODO();
+}
+
+JS::NonnullGCPtr<SVGAnimatedLength> SVGUseElement::height() const
+{
+    TODO();
+}
+
+// https://svgwg.org/svg2-draft/struct.html#TermInstanceRoot
+JS::GCPtr<SVGElement> SVGUseElement::instance_root() const
+{
+    return shadow_root()->first_child_of_type<SVGElement>();
+}
+
+JS::GCPtr<SVGElement> SVGUseElement::animated_instance_root() const
+{
+    return instance_root();
+}
+
+}
diff --git a/Userland/Libraries/LibWeb/SVG/SVGUseElement.h b/Userland/Libraries/LibWeb/SVG/SVGUseElement.h
new file mode 100644
index 0000000000..eb118db513
--- /dev/null
+++ b/Userland/Libraries/LibWeb/SVG/SVGUseElement.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2023, Preston Taylor <95388976+PrestonLTaylor@users.noreply.github.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGfx/Path.h>
+#include <LibWeb/DOM/DocumentObserver.h>
+#include <LibWeb/SVG/SVGAnimatedLength.h>
+#include <LibWeb/SVG/SVGGraphicsElement.h>
+
+namespace Web::SVG {
+
+class SVGUseElement final : public SVGGraphicsElement {
+    WEB_PLATFORM_OBJECT(SVGUseElement, SVGGraphicsElement);
+
+public:
+    virtual ~SVGUseElement() override = default;
+
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
+
+    virtual void inserted() override;
+
+    void svg_element_changed(SVGElement&);
+    void svg_element_removed(SVGElement&);
+
+    JS::NonnullGCPtr<SVGAnimatedLength> x() const;
+    JS::NonnullGCPtr<SVGAnimatedLength> y() const;
+    JS::NonnullGCPtr<SVGAnimatedLength> width() const;
+    JS::NonnullGCPtr<SVGAnimatedLength> height() const;
+
+    JS::GCPtr<SVGElement> instance_root() const;
+    JS::GCPtr<SVGElement> animated_instance_root() const;
+
+private:
+    SVGUseElement(DOM::Document&, DOM::QualifiedName);
+
+    virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
+    virtual void visit_edges(Cell::Visitor&) override;
+
+    Optional<StringView> parse_id_from_href(DeprecatedString const& href);
+
+    JS::GCPtr<DOM::Element> referenced_element();
+
+    void clone_element_tree_as_our_shadow_tree(Element* to_clone) const;
+    bool is_valid_reference_element(Element* reference_element) const;
+
+    Optional<float> m_x;
+    Optional<float> m_y;
+
+    Optional<StringView> m_referenced_id;
+
+    JS::GCPtr<DOM::DocumentObserver> m_document_observer;
+};
+
+}
diff --git a/Userland/Libraries/LibWeb/SVG/SVGUseElement.idl b/Userland/Libraries/LibWeb/SVG/SVGUseElement.idl
new file mode 100644
index 0000000000..37de82fefd
--- /dev/null
+++ b/Userland/Libraries/LibWeb/SVG/SVGUseElement.idl
@@ -0,0 +1,16 @@
+#import <SVG/SVGAnimatedLength.idl>
+#import <SVG/SVGElement.idl>
+#import <SVG/SVGGraphicsElement.idl>
+
+// https://svgwg.org/svg2-draft/struct.html#InterfaceSVGUseElement
+[Exposed=Window]
+interface SVGUseElement : SVGGraphicsElement {
+  [SameObject] readonly attribute SVGAnimatedLength x;
+  [SameObject] readonly attribute SVGAnimatedLength y;
+  [SameObject] readonly attribute SVGAnimatedLength width;
+  [SameObject] readonly attribute SVGAnimatedLength height;
+  [SameObject] readonly attribute SVGElement? instanceRoot;
+  [SameObject] readonly attribute SVGElement? animatedInstanceRoot;
+};
+
+// FIXME: SVGUseElement includes SVGURIReference;
diff --git a/Userland/Libraries/LibWeb/SVG/TagNames.h b/Userland/Libraries/LibWeb/SVG/TagNames.h
index 85712cad39..9034987c81 100644
--- a/Userland/Libraries/LibWeb/SVG/TagNames.h
+++ b/Userland/Libraries/LibWeb/SVG/TagNames.h
@@ -33,7 +33,8 @@ namespace Web::SVG::TagNames {
     __ENUMERATE_SVG_TAG(radialGradient) \
     __ENUMERATE_SVG_TAG(script)         \
     __ENUMERATE_SVG_TAG(stop)           \
-    __ENUMERATE_SVG_TAG(title)
+    __ENUMERATE_SVG_TAG(title)          \
+    __ENUMERATE_SVG_TAG(use)
 
 #define __ENUMERATE_SVG_TAG(name) extern DeprecatedFlyString name;
 ENUMERATE_SVG_TAGS
diff --git a/Userland/Libraries/LibWeb/idl_files.cmake b/Userland/Libraries/LibWeb/idl_files.cmake
index 69da343304..53a5076bbb 100644
--- a/Userland/Libraries/LibWeb/idl_files.cmake
+++ b/Userland/Libraries/LibWeb/idl_files.cmake
@@ -212,6 +212,7 @@ libweb_js_bindings(SVG/SVGRectElement)
 libweb_js_bindings(SVG/SVGSVGElement)
 libweb_js_bindings(SVG/SVGStopElement)
 libweb_js_bindings(SVG/SVGTextContentElement)
+libweb_js_bindings(SVG/SVGUseElement)
 libweb_js_bindings(Selection/Selection)
 libweb_js_bindings(UIEvents/FocusEvent)
 libweb_js_bindings(UIEvents/KeyboardEvent)