LibWeb: Add 'Run the fullscreen steps'

Run the fullscreen steps is an event-dispatching algorithm, which we
implement here. Future work will populate the pending list with events.

Libraries/LibWeb/DOM/Document.cpp

@@ -582,6 +582,10 @@ void Document::visit_edges(Cell::Visitor& visitor)
         visitor.visit(event.target);
     }
 
+    for (auto& event : m_pending_fullscreen_events) {
+        visitor.visit(event.element);
+    }
+
     visitor.visit(m_adopted_style_sheets);
 
     for (auto& shadow_root : m_shadow_roots)
@@ -6209,6 +6213,39 @@ void Document::remove_render_blocking_element(GC::Ref<Element> element)
     m_render_blocking_elements.remove(element);
 }
 
+// https://fullscreen.spec.whatwg.org/#run-the-fullscreen-steps
+void Document::run_fullscreen_steps()
+{
+    // 1. Let pendingEvents be document’s list of pending fullscreen events.
+    // 2. Empty document’s list of pending fullscreen events.
+    Vector<PendingFullscreenEvent> pending_events;
+    std::swap(m_pending_fullscreen_events, pending_events);
+    // 3. For each (type, element) in pendingEvents:
+    for (auto const& [type, element] : pending_events) {
+        // 1. Let target be element if element is connected and its node document is document, and otherwise let target be document.
+        EventTarget* target = nullptr;
+        if (element->is_connected() && &element->document() == this) {
+            target = element;
+        } else {
+            target = this;
+        }
+        // 2. Fire an event named type, with its bubbles and composed attributes set to true, at target.
+        switch (type) {
+        case PendingFullscreenEvent::Type::Change:
+            target->dispatch_event(Event::create(realm(), HTML::EventNames::fullscreenchange, EventInit { .bubbles = true, .composed = true }));
+            break;
+        case PendingFullscreenEvent::Type::Error:
+            target->dispatch_event(Event::create(realm(), HTML::EventNames::fullscreenerror, EventInit { .bubbles = true, .composed = true }));
+            break;
+        }
+    }
+}
+
+void Document::append_pending_fullscreen_change(PendingFullscreenEvent::Type type, GC::Ref<Element> element)
+{
+    m_pending_fullscreen_events.append(PendingFullscreenEvent { type, element });
+}
+
 // https://dom.spec.whatwg.org/#document-allow-declarative-shadow-roots
 void Document::set_allow_declarative_shadow_roots(bool allow)
 {

Libraries/LibWeb/DOM/Document.h

@@ -156,6 +156,14 @@ enum class PolicyControlledFeature : u8 {
     FocusWithoutUserActivation,
 };
 
+struct PendingFullscreenEvent {
+    enum class Type {
+        Change,
+        Error,
+    } type;
+    GC::Ref<Element> element;
+};
+
 class Document
     : public ParentNode
     , public HTML::GlobalEventHandlers {
@@ -896,6 +904,9 @@ public:
     }
 
     ElementByIdMap& element_by_id() const;
+    // https://fullscreen.spec.whatwg.org/#run-the-fullscreen-steps
+    void run_fullscreen_steps();
+    void append_pending_fullscreen_change(PendingFullscreenEvent::Type type, GC::Ref<Element> element);
 
 protected:
     virtual void initialize(JS::Realm&) override;
@@ -1249,6 +1260,8 @@ private:
     HashTable<GC::Ref<Element>> m_render_blocking_elements;
 
     HashTable<WeakPtr<Node>> m_pending_nodes_for_style_invalidation_due_to_presence_of_has;
+    // https://fullscreen.spec.whatwg.org/#list-of-pending-fullscreen-events
+    Vector<PendingFullscreenEvent> m_pending_fullscreen_events;
 };
 
 template<>

Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp

@@ -379,7 +379,10 @@ void EventLoop::update_the_rendering()
         document->update_animations_and_send_events(HighResolutionTime::relative_high_resolution_time(frame_timestamp, relevant_global_object(*document)));
     };
 
-    // FIXME: 12. For each doc of docs, run the fullscreen steps for doc. [FULLSCREEN]
+    // 12. For each doc of docs, run the fullscreen steps for doc. [FULLSCREEN]
+    for (auto& document : docs) {
+        document->run_fullscreen_steps();
+    }
 
     // FIXME: 13. For each doc of docs, if the user agent detects that the backing storage associated with a CanvasRenderingContext2D or an OffscreenCanvasRenderingContext2D, context, has been lost, then it must run the context lost steps for each such context:
 

Libraries/LibWeb/HTML/EventNames.h

@@ -62,6 +62,8 @@ namespace Web::HTML::EventNames {
     __ENUMERATE_HTML_EVENT(focusin)                  \
     __ENUMERATE_HTML_EVENT(focusout)                 \
     __ENUMERATE_HTML_EVENT(formdata)                 \
+    __ENUMERATE_HTML_EVENT(fullscreenchange)         \
+    __ENUMERATE_HTML_EVENT(fullscreenerror)          \
     __ENUMERATE_HTML_EVENT(hashchange)               \
     __ENUMERATE_HTML_EVENT(input)                    \
     __ENUMERATE_HTML_EVENT(invalid)                  \