LibWeb: Implement basic "scroll" events at the document level

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -323,6 +323,11 @@ void Document::visit_edges(Cell::Visitor& visitor)
 
     for (auto& node_iterator : m_node_iterators)
         visitor.visit(node_iterator);
+
+    for (auto& target : m_pending_scroll_event_targets)
+        visitor.visit(target.ptr());
+    for (auto& target : m_pending_scrollend_event_targets)
+        visitor.visit(target.ptr());
 }
 
 // https://html.spec.whatwg.org/multipage/dynamic-markup-insertion.html#dom-document-write
@@ -1570,6 +1575,29 @@ void Document::run_the_resize_steps()
     update_layout();
 }
 
+// https://w3c.github.io/csswg-drafts/cssom-view-1/#document-run-the-scroll-steps
+void Document::run_the_scroll_steps()
+{
+    // 1. For each item target in doc’s pending scroll event targets, in the order they were added to the list, run these substeps:
+    for (auto& target : m_pending_scroll_event_targets) {
+        // 1. If target is a Document, fire an event named scroll that bubbles at target and fire an event named scroll at the VisualViewport that is associated with target.
+        if (is<Document>(*target)) {
+            auto event = DOM::Event::create(window(), HTML::EventNames::scroll);
+            event->set_bubbles(true);
+            target->dispatch_event(*event);
+            // FIXME: Fire at the associated VisualViewport
+        }
+        // 2. Otherwise, fire an event named scroll at target.
+        else {
+            auto event = DOM::Event::create(window(), HTML::EventNames::scroll);
+            target->dispatch_event(*event);
+        }
+    }
+
+    // 2. Empty doc’s pending scroll event targets.
+    m_pending_scroll_event_targets.clear();
+}
+
 void Document::add_media_query_list(JS::NonnullGCPtr<CSS::MediaQueryList> media_query_list)
 {
     m_media_query_lists.append(*media_query_list);

Userland/Libraries/LibWeb/DOM/Document.h

@@ -317,6 +317,7 @@ public:
     String visibility_state() const;
 
     void run_the_resize_steps();
+    void run_the_scroll_steps();
 
     void evaluate_media_queries_and_report_changes();
     void add_media_query_list(JS::NonnullGCPtr<CSS::MediaQueryList>);
@@ -360,6 +361,9 @@ public:
     String domain() const;
     void set_domain(String const& domain);
 
+    auto& pending_scroll_event_targets() { return m_pending_scroll_event_targets; }
+    auto& pending_scrollend_event_targets() { return m_pending_scrollend_event_targets; }
+
 protected:
     virtual void visit_edges(Cell::Visitor&) override;
 
@@ -456,6 +460,12 @@ private:
     // Used by run_the_resize_steps().
     Gfx::IntSize m_last_viewport_size;
 
+    // https://w3c.github.io/csswg-drafts/cssom-view-1/#document-pending-scroll-event-targets
+    Vector<JS::NonnullGCPtr<EventTarget>> m_pending_scroll_event_targets;
+
+    // https://w3c.github.io/csswg-drafts/cssom-view-1/#document-pending-scrollend-event-targets
+    Vector<JS::NonnullGCPtr<EventTarget>> m_pending_scrollend_event_targets;
+
     // Used by evaluate_media_queries_and_report_changes().
     Vector<WeakPtr<CSS::MediaQueryList>> m_media_query_lists;
 

Userland/Libraries/LibWeb/HTML/BrowsingContext.cpp

@@ -320,6 +320,7 @@ void BrowsingContext::set_viewport_rect(Gfx::IntRect const& rect)
 
     if (m_viewport_scroll_offset != rect.location()) {
         m_viewport_scroll_offset = rect.location();
+        scroll_offset_did_change();
         did_change = true;
     }
 
@@ -785,4 +786,23 @@ DOM::Document* BrowsingContext::active_document()
     return m_active_document.cell();
 }
 
+void BrowsingContext::scroll_offset_did_change()
+{
+    // https://w3c.github.io/csswg-drafts/cssom-view-1/#scrolling-events
+    // Whenever a viewport gets scrolled (whether in response to user interaction or by an API), the user agent must run these steps:
+
+    // 1. Let doc be the viewport’s associated Document.
+    auto* doc = active_document();
+    VERIFY(doc);
+
+    // 2. If doc is already in doc’s pending scroll event targets, abort these steps.
+    for (auto& target : doc->pending_scroll_event_targets()) {
+        if (target.ptr() == doc)
+            return;
+    }
+
+    // 3. Append doc to doc’s pending scroll event targets.
+    doc->pending_scroll_event_targets().append(*doc);
+}
+
 }

Userland/Libraries/LibWeb/HTML/BrowsingContext.h

@@ -129,6 +129,8 @@ private:
 
     void reset_cursor_blink_cycle();
 
+    void scroll_offset_did_change();
+
     WeakPtr<Page> m_page;
 
     FrameLoader m_loader;

Userland/Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp

@@ -169,7 +169,10 @@ void EventLoop::process()
         document.run_the_resize_steps();
     });
 
-    // FIXME:     8. For each fully active Document in docs, run the scroll steps for that Document, passing in now as the timestamp. [CSSOMVIEW]
+    // 8. For each fully active Document in docs, run the scroll steps for that Document, passing in now as the timestamp. [CSSOMVIEW]
+    for_each_fully_active_document_in_docs([&](DOM::Document& document) {
+        document.run_the_scroll_steps();
+    });
 
     // 9. For each fully active Document in docs, evaluate media queries and report changes for that Document, passing in now as the timestamp. [CSSOMVIEW]
     for_each_fully_active_document_in_docs([&](DOM::Document& document) {

Userland/Libraries/LibWeb/HTML/EventNames.h

@@ -49,6 +49,7 @@ namespace Web::HTML::EventNames {
     __ENUMERATE_HTML_EVENT(readystatechange)        \
     __ENUMERATE_HTML_EVENT(rejectionhandled)        \
     __ENUMERATE_HTML_EVENT(reset)                   \
+    __ENUMERATE_HTML_EVENT(scroll)                  \
     __ENUMERATE_HTML_EVENT(securitypolicyviolation) \
     __ENUMERATE_HTML_EVENT(select)                  \
     __ENUMERATE_HTML_EVENT(slotchange)              \