LibWeb: Add <canvas> element and start fleshing out CRC2D

This patch adds HTMLCanvasElement along with a LayoutCanvas object.
The DOM and layout parts are very similar to <img> elements.

The <canvas> element holds a Gfx::Bitmap which is sized according to
the "width" and "height" attributes on the element.

Calling .getContext("2d") on a <canvas> element gives you a context
object that draws into the underlying Gfx::Bitmap of the <canvas>.
The context weakly points to the <canvas> which allows it to outlive
the canvas element if needed.

This is really quite cool. :^)

Libraries/LibWeb/DOM/CanvasRenderingContext2D.cpp

@@ -0,0 +1,44 @@
+#include <AK/OwnPtr.h>
+#include <LibGfx/Painter.h>
+#include <LibWeb/DOM/CanvasRenderingContext2D.h>
+#include <LibWeb/DOM/HTMLCanvasElement.h>
+
+namespace Web {
+
+CanvasRenderingContext2D::CanvasRenderingContext2D(HTMLCanvasElement& element)
+    : m_element(element.make_weak_ptr())
+{
+}
+
+CanvasRenderingContext2D::~CanvasRenderingContext2D()
+{
+}
+
+void CanvasRenderingContext2D::set_fill_style(String style)
+{
+    m_fill_style = Gfx::Color::from_string(style).value_or(Color::Black);
+}
+
+String CanvasRenderingContext2D::fill_style() const
+{
+    return m_fill_style.to_string();
+}
+
+void CanvasRenderingContext2D::fill_rect(int x, int y, int width, int height)
+{
+    auto painter = this->painter();
+    if (!painter)
+        return;
+
+    painter->fill_rect({ x, y, width, height }, m_fill_style);
+}
+
+OwnPtr<Gfx::Painter> CanvasRenderingContext2D::painter()
+{
+    if (!m_element)
+        return nullptr;
+
+    return make<Gfx::Painter>(m_element->ensure_bitmap());
+}
+
+}

Libraries/LibWeb/DOM/CanvasRenderingContext2D.h

@@ -0,0 +1,38 @@
+#pragma once
+
+#include <AK/RefCounted.h>
+#include <LibGfx/Color.h>
+#include <LibGfx/Forward.h>
+#include <LibWeb/Bindings/Wrappable.h>
+
+namespace Web {
+
+class CanvasRenderingContext2D
+    : public RefCounted<CanvasRenderingContext2D>
+    , public Bindings::Wrappable {
+
+    AK_MAKE_NONCOPYABLE(CanvasRenderingContext2D);
+    AK_MAKE_NONMOVABLE(CanvasRenderingContext2D);
+
+public:
+    using WrapperType = Bindings::CanvasRenderingContext2DWrapper;
+
+    static NonnullRefPtr<CanvasRenderingContext2D> create(HTMLCanvasElement& element) { return adopt(*new CanvasRenderingContext2D(element)); }
+    ~CanvasRenderingContext2D();
+
+    void set_fill_style(String);
+    String fill_style() const;
+
+    void fill_rect(int x, int y, int width, int height);
+
+private:
+    explicit CanvasRenderingContext2D(HTMLCanvasElement&);
+
+    OwnPtr<Gfx::Painter> painter();
+
+    WeakPtr<HTMLCanvasElement> m_element;
+
+    Gfx::Color m_fill_style;
+};
+
+}

Libraries/LibWeb/DOM/ElementFactory.cpp

@@ -29,6 +29,7 @@
 #include <LibWeb/DOM/HTMLBRElement.h>
 #include <LibWeb/DOM/HTMLBlinkElement.h>
 #include <LibWeb/DOM/HTMLBodyElement.h>
+#include <LibWeb/DOM/HTMLCanvasElement.h>
 #include <LibWeb/DOM/HTMLFontElement.h>
 #include <LibWeb/DOM/HTMLFormElement.h>
 #include <LibWeb/DOM/HTMLHRElement.h>
@@ -85,6 +86,8 @@ NonnullRefPtr<Element> create_element(Document& document, const String& tag_name
     }
     if (lowercase_tag_name == "script")
         return adopt(*new HTMLScriptElement(document, lowercase_tag_name));
+    if (lowercase_tag_name == "canvas")
+        return adopt(*new HTMLCanvasElement(document, lowercase_tag_name));
     return adopt(*new Element(document, lowercase_tag_name));
 }
 

Libraries/LibWeb/DOM/HTMLCanvasElement.cpp

@@ -0,0 +1,92 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * 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/Bitmap.h>
+#include <LibWeb/CSS/StyleResolver.h>
+#include <LibWeb/DOM/CanvasRenderingContext2D.h>
+#include <LibWeb/DOM/Document.h>
+#include <LibWeb/DOM/HTMLCanvasElement.h>
+#include <LibWeb/Layout/LayoutCanvas.h>
+
+namespace Web {
+
+HTMLCanvasElement::HTMLCanvasElement(Document& document, const String& tag_name)
+    : HTMLElement(document, tag_name)
+{
+}
+
+HTMLCanvasElement::~HTMLCanvasElement()
+{
+}
+
+int HTMLCanvasElement::preferred_width() const
+{
+    bool ok = false;
+    int width = attribute("width").to_int(ok);
+    if (ok)
+        return width;
+
+    return 300;
+}
+
+int HTMLCanvasElement::preferred_height() const
+{
+    bool ok = false;
+    int height = attribute("height").to_int(ok);
+    if (ok)
+        return height;
+
+    return 300;
+}
+
+RefPtr<LayoutNode> HTMLCanvasElement::create_layout_node(const StyleProperties* parent_style) const
+{
+    auto style = document().style_resolver().resolve_style(*this, parent_style);
+    auto display = style->string_or_fallback(CSS::PropertyID::Display, "inline");
+    if (display == "none")
+        return nullptr;
+    return adopt(*new LayoutCanvas(*this, move(style)));
+}
+
+CanvasRenderingContext2D* HTMLCanvasElement::get_context(String type)
+{
+    ASSERT(type.to_lowercase() == "2d");
+    dbg() << "get_context with m_context=" << m_context.ptr();
+    if (!m_context)
+        m_context = CanvasRenderingContext2D::create(*this);
+    dbg() << "get_context returning m_context=" << m_context.ptr();
+    return m_context;
+}
+
+Gfx::Bitmap& HTMLCanvasElement::ensure_bitmap()
+{
+    if (!m_bitmap || m_bitmap->size() != Gfx::Size(preferred_width(), preferred_height())) {
+        m_bitmap = Gfx::Bitmap::create(Gfx::BitmapFormat::RGBA32, { preferred_width(), preferred_height() });
+    }
+    return *m_bitmap;
+}
+
+}

Libraries/LibWeb/DOM/HTMLCanvasElement.h

@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * 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.
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <LibGfx/Forward.h>
+#include <LibWeb/DOM/HTMLElement.h>
+
+namespace Web {
+
+class LayoutDocument;
+
+class HTMLCanvasElement : public HTMLElement {
+public:
+    using WrapperType = Bindings::HTMLCanvasElementWrapper;
+
+    HTMLCanvasElement(Document&, const String& tag_name);
+    virtual ~HTMLCanvasElement() override;
+
+    int preferred_width() const;
+    int preferred_height() const;
+
+    const Gfx::Bitmap* bitmap() const { return m_bitmap; }
+    Gfx::Bitmap& ensure_bitmap();
+
+    CanvasRenderingContext2D* get_context(String type);
+
+private:
+    virtual RefPtr<LayoutNode> create_layout_node(const StyleProperties* parent_style) const override;
+
+    RefPtr<Gfx::Bitmap> m_bitmap;
+    RefPtr<CanvasRenderingContext2D> m_context;
+};
+
+template<>
+inline bool is<HTMLCanvasElement>(const Node& node)
+{
+    return is<Element>(node) && to<Element>(node).tag_name().to_lowercase() == "canvas";
+}
+
+
+}