LibWeb: Add SVG <circle> element and test case :^)

Userland/Libraries/LibWeb/SVG/AttributeNames.h

@@ -19,6 +19,8 @@ namespace Web::SVG::AttributeNames {
     E(clipPathUnits)                \
     E(contentScriptType)            \
     E(contentStyleType)             \
+    E(cx)                           \
+    E(cy)                           \
     E(diffuseConstant)              \
     E(edgeMode)                     \
     E(filterUnits)                  \
@@ -49,6 +51,7 @@ namespace Web::SVG::AttributeNames {
     E(preserveAlpha)                \
     E(preserveAspectRatio)          \
     E(primitiveUnits)               \
+    E(r)                            \
     E(refX)                         \
     E(refY)                         \
     E(repeatCount)                  \

Userland/Libraries/LibWeb/SVG/SVGCircleElement.cpp

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "SVGCircleElement.h"
+#include <LibWeb/SVG/AttributeNames.h>
+#include <LibWeb/SVG/AttributeParser.h>
+
+namespace Web::SVG {
+
+SVGCircleElement::SVGCircleElement(DOM::Document& document, QualifiedName qualified_name)
+    : SVGGeometryElement(document, qualified_name)
+{
+}
+
+void SVGCircleElement::parse_attribute(FlyString const& name, String const& value)
+{
+    SVGGeometryElement::parse_attribute(name, value);
+
+    if (name == SVG::AttributeNames::cx) {
+        m_center_x = AttributeParser::parse_coordinate(value);
+        m_path.clear();
+    } else if (name == SVG::AttributeNames::cy) {
+        m_center_y = AttributeParser::parse_coordinate(value);
+        m_path.clear();
+    } else if (name == SVG::AttributeNames::r) {
+        m_radius = AttributeParser::parse_positive_length(value);
+        m_path.clear();
+    }
+}
+
+Gfx::Path& SVGCircleElement::get_path()
+{
+    if (m_path.has_value())
+        return m_path.value();
+
+    float cx = m_center_x.value_or(0);
+    float cy = m_center_y.value_or(0);
+    float r = m_radius.value_or(0);
+
+    Gfx::Path path;
+
+    // A zero radius disables rendering.
+    if (r == 0) {
+        m_path = move(path);
+        return m_path.value();
+    }
+
+    bool large_arc = false;
+    bool sweep = true;
+
+    // 1. A move-to command to the point cx+r,cy;
+    path.move_to({ cx + r, cy });
+
+    // 2. arc to cx,cy+r;
+    path.arc_to({ cx, cy + r }, r, large_arc, sweep);
+
+    // 3. arc to cx-r,cy;
+    path.arc_to({ cx - r, cy }, r, large_arc, sweep);
+
+    // 4. arc to cx,cy-r;
+    path.arc_to({ cx, cy - r }, r, large_arc, sweep);
+
+    // 5. arc with a segment-completing close path operation.
+    path.arc_to({ cx + r, cy }, r, large_arc, sweep);
+
+    m_path = move(path);
+    return m_path.value();
+}
+
+}

Userland/Libraries/LibWeb/SVG/SVGCircleElement.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/SVG/SVGGeometryElement.h>
+
+namespace Web::SVG {
+
+class SVGCircleElement final : public SVGGeometryElement {
+public:
+    using WrapperType = Bindings::SVGCircleElementWrapper;
+
+    SVGCircleElement(DOM::Document&, QualifiedName);
+    virtual ~SVGCircleElement() override = default;
+
+    virtual void parse_attribute(FlyString const& name, String const& value) override;
+
+    virtual Gfx::Path& get_path() override;
+
+private:
+    Optional<Gfx::Path> m_path;
+
+    Optional<float> m_center_x;
+    Optional<float> m_center_y;
+    Optional<float> m_radius;
+};
+
+}

Userland/Libraries/LibWeb/SVG/SVGCircleElement.idl

@@ -0,0 +1,6 @@
+[Exposed=Window]
+interface SVGCircleElement : SVGGeometryElement {
+    // [SameObject] readonly attribute SVGAnimatedLength cx;
+    // [SameObject] readonly attribute SVGAnimatedLength cy;
+    // [SameObject] readonly attribute SVGAnimatedLength r;
+};

Userland/Libraries/LibWeb/SVG/TagNames.h

@@ -11,6 +11,7 @@
 namespace Web::SVG::TagNames {
 
 #define ENUMERATE_SVG_GRAPHICS_TAGS \
+    __ENUMERATE_SVG_TAG(circle)     \
     __ENUMERATE_SVG_TAG(g)          \
     __ENUMERATE_SVG_TAG(path)       \
     __ENUMERATE_SVG_TAG(rect)       \