LibWeb: Begin SVG element support

This commit starts adding a basic SVG element. Currently, svg elements
have support for the width and height properties, as well as the stroke,
stroke-width, and fill properties. The only child element supported
is the path element, as most other graphical elements are just shorthand
for paths.

Libraries/LibWeb/DOM/HTMLSvgElement.cpp

@@ -0,0 +1,151 @@
+/*
+ * Copyright (c) 2020, Matthew Olsson <matthewcolsson@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <LibGfx/Path.h>
+#include <LibWeb/CSS/StyleResolver.h>
+#include <LibWeb/DOM/Document.h>
+#include <LibWeb/DOM/Event.h>
+#include <LibWeb/DOM/HTMLPathElement.h>
+#include <LibWeb/DOM/HTMLSvgElement.h>
+#include <LibWeb/Layout/LayoutSvg.h>
+#include <ctype.h>
+
+namespace Web {
+
+static constexpr auto max_svg_area = 16384 * 16384;
+
+HTMLSvgElement::HTMLSvgElement(Document& document, const FlyString& tag_name)
+    : HTMLElement(document, tag_name)
+{
+}
+
+void HTMLSvgElement::parse_attribute(const FlyString& name, const String& value)
+{
+    HTMLElement::parse_attribute(name, value);
+    if (name == "stroke") {
+        m_stroke_color = Gfx::Color::from_string(value);
+    } else if (name == "stroke-width") {
+        auto result = value.to_int();
+        if (result.has_value())
+            m_stroke_width = result.value();
+    } else if (name == "fill") {
+        m_fill_color = Gfx::Color::from_string(value);
+    }
+}
+
+RefPtr<LayoutNode> HTMLSvgElement::create_layout_node(const StyleProperties* parent_style)
+{
+    auto style = document().style_resolver().resolve_style(*this, parent_style);
+    if (style->display() == CSS::Display::None)
+        return nullptr;
+    return adopt(*new LayoutSvg(document(), *this, move(style)));
+}
+
+static Gfx::IntSize bitmap_size_for_canvas(const HTMLSvgElement& canvas)
+{
+    auto width = canvas.width();
+    auto height = canvas.height();
+
+    Checked<size_t> area = width;
+    area *= height;
+
+    if (area.has_overflow()) {
+        dbg() << "Refusing to create " << width << "x" << height << " svg (overflow)";
+        return {};
+    }
+    if (area.value() > max_svg_area) {
+        dbg() << "Refusing to create " << width << "x" << height << " svg (exceeds maximum size)";
+        return {};
+    }
+    return Gfx::IntSize(width, height);
+}
+
+bool HTMLSvgElement::create_bitmap()
+{
+    auto size = bitmap_size_for_canvas(*this);
+    if (size.is_empty()) {
+        m_bitmap = nullptr;
+        return false;
+    }
+
+    if (!m_bitmap || m_bitmap->size() != size)
+        m_bitmap = Gfx::Bitmap::create(Gfx::BitmapFormat::RGBA32, size);
+
+    Gfx::Painter painter(*m_bitmap);
+    paint(painter);
+
+    return m_bitmap;
+}
+
+SvgPaintingContext HTMLSvgElement::make_context() const
+{
+    SvgPaintingContext context;
+
+    if (m_stroke_width.has_value())
+        context.stroke_width = m_stroke_width.value();
+    if (m_stroke_color.has_value())
+        context.stroke_color = m_stroke_color.value();
+    if (m_fill_color.has_value())
+        context.fill_color = m_fill_color.value();
+
+    return context;
+}
+
+unsigned HTMLSvgElement::width() const
+{
+    return attribute(HTML::AttributeNames::width).to_uint().value_or(300);
+}
+
+unsigned HTMLSvgElement::height() const
+{
+    return attribute(HTML::AttributeNames::height).to_uint().value_or(150);
+}
+
+static bool is_svg_graphic_element(const HTMLElement& element)
+{
+    return is<HTMLPathElement>(element);
+}
+
+static SvgGraphicElement& as_svg_graphic_element(HTMLElement& element)
+{
+    if (is<HTMLPathElement>(element))
+        return to<HTMLPathElement>(element);
+    ASSERT_NOT_REACHED();
+}
+
+void HTMLSvgElement::paint(Gfx::Painter& painter)
+{
+    for_each_child([&](Node& child) {
+        if (is<HTMLElement>(child)) {
+            auto& element = to<HTMLElement>(child);
+            if (is_svg_graphic_element(element)) {
+                as_svg_graphic_element(element).paint(make_context(), painter);
+            }
+        }
+    });
+}
+
+}