LibWeb: Share decoded images at the Resource level :^)

This patch adds ImageResource as a subclass of Resource. This new class
also keeps a Gfx::ImageDecoder so that we can share decoded bitmaps
between all clients of an image resource inside LibWeb.

With this, we now share both encoded and decoded data for images. :^)

I had to change how the purgeable-volatile flag is updated to keep the
volatile-images-outside-the-visible-viewport optimization working.
HTMLImageElement now inherits from ImageResourceClient (a subclass of
ResourceClient with additional image-specific stuff) and informs its
ImageResource about whether it's inside the viewport or outside.

This is pretty awesome! :^)

Libraries/LibWeb/DOM/HTMLImageElement.cpp

@@ -56,7 +56,7 @@ void HTMLImageElement::load_image(const String& src)
 {
     LoadRequest request;
     request.set_url(document().complete_url(src));
-    set_resource(ResourceLoader::the().load_resource(request));
+    set_resource(ResourceLoader::the().load_resource(Resource::Type::Image, request));
 }
 
 void HTMLImageElement::resource_did_load()
@@ -70,7 +70,8 @@ void HTMLImageElement::resource_did_load()
 
     dbg() << "HTMLImageElement: Resource did load, encoded data looks tasty: " << this->src();
 
-    m_image_decoder = Gfx::ImageDecoder::create(resource()->encoded_data());
+    ASSERT(!m_image_decoder);
+    m_image_decoder = resource()->ensure_decoder();
 
     if (m_image_decoder->is_animated() && m_image_decoder->frame_count() > 1) {
         const auto& first_frame = m_image_decoder->frame(0);
@@ -91,6 +92,11 @@ void HTMLImageElement::resource_did_fail()
     dispatch_event(Event::create("error"));
 }
 
+void HTMLImageElement::resource_did_replace_decoder()
+{
+    m_image_decoder = resource()->ensure_decoder();
+}
+
 void HTMLImageElement::animate()
 {
     if (!layout_node()) {
@@ -161,19 +167,17 @@ const Gfx::Bitmap* HTMLImageElement::bitmap() const
     return m_image_decoder->bitmap();
 }
 
-void HTMLImageElement::set_volatile(Badge<LayoutDocument>, bool v)
+void HTMLImageElement::set_visible_in_viewport(Badge<LayoutDocument>, bool visible_in_viewport)
 {
-    if (!m_image_decoder)
+    if (m_visible_in_viewport == visible_in_viewport)
         return;
-    if (v) {
-        m_image_decoder->set_volatile();
-        return;
-    }
-    bool has_image = m_image_decoder->set_nonvolatile();
-    if (has_image)
-        return;
-    ASSERT(resource());
-    m_image_decoder = Gfx::ImageDecoder::create(resource()->encoded_data());
+    m_visible_in_viewport = visible_in_viewport;
+
+    // FIXME: Don't update volatility every time. If we're here, we're probably scanning through
+    //        the whole document, updating "is visible in viewport" flags, and this could lead
+    //        to the same bitmap being marked volatile back and forth unnecessarily.
+    if (resource())
+        resource()->update_volatility();
 }
 
 }

Libraries/LibWeb/DOM/HTMLImageElement.h

@@ -30,7 +30,7 @@
 #include <LibCore/Forward.h>
 #include <LibGfx/Forward.h>
 #include <LibWeb/DOM/HTMLElement.h>
-#include <LibWeb/Loader/Resource.h>
+#include <LibWeb/Loader/ImageResource.h>
 
 namespace Web {
 
@@ -38,7 +38,7 @@ class LayoutDocument;
 
 class HTMLImageElement final
     : public HTMLElement
-    , public ResourceClient {
+    , public ImageResourceClient {
 public:
     using WrapperType = Bindings::HTMLImageElementWrapper;
 
@@ -55,11 +55,14 @@ public:
     const Gfx::Bitmap* bitmap() const;
     const Gfx::ImageDecoder* image_decoder() const { return m_image_decoder; }
 
-    void set_volatile(Badge<LayoutDocument>, bool);
+    void set_visible_in_viewport(Badge<LayoutDocument>, bool);
 
 private:
+    // ^ImageResource
     virtual void resource_did_load() override;
     virtual void resource_did_fail() override;
+    virtual void resource_did_replace_decoder() override;
+    virtual bool is_visible_in_viewport() const override { return m_visible_in_viewport; }
 
     void load_image(const String& src);
 
@@ -72,6 +75,8 @@ private:
     size_t m_current_frame_index { 0 };
     size_t m_loops_completed { 0 };
     NonnullRefPtr<Core::Timer> m_timer;
+
+    bool m_visible_in_viewport { false };
 };
 
 template<>

Libraries/LibWeb/DOM/HTMLLinkElement.cpp

@@ -76,7 +76,7 @@ void HTMLLinkElement::load_stylesheet(const URL& url)
 {
     LoadRequest request;
     request.set_url(url);
-    set_resource(ResourceLoader::the().load_resource(request));
+    set_resource(ResourceLoader::the().load_resource(Resource::Type::Generic, request));
 }
 
 }