LibWeb: Let HTML::EventLoop drive the firing of resize events

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/6e341cd6962

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -57,6 +57,7 @@
 #include <LibWeb/Page/BrowsingContext.h>
 #include <LibWeb/Page/Page.h>
 #include <LibWeb/SVG/TagNames.h>
+#include <LibWeb/UIEvents/EventNames.h>
 #include <LibWeb/UIEvents/KeyboardEvent.h>
 #include <LibWeb/UIEvents/MouseEvent.h>
 
@@ -1083,4 +1084,25 @@ String Document::visibility_state() const
     return hidden() ? "hidden" : "visible";
 }
 
+// https://drafts.csswg.org/cssom-view/#run-the-resize-steps
+void Document::run_the_resize_steps()
+{
+    // 1. If doc’s viewport has had its width or height changed
+    //    (e.g. as a result of the user resizing the browser window, or changing the page zoom scale factor,
+    //    or an iframe element’s dimensions are changed) since the last time these steps were run,
+    //    fire an event named resize at the Window object associated with doc.
+
+    if (!browsing_context())
+        return;
+
+    auto viewport_size = browsing_context()->viewport_rect().size();
+    if (m_last_viewport_size == viewport_size)
+        return;
+    m_last_viewport_size = viewport_size;
+
+    dispatch_event(DOM::Event::create(UIEvents::EventNames::resize));
+
+    update_layout();
+}
+
 }

Userland/Libraries/LibWeb/DOM/Document.h

@@ -301,6 +301,8 @@ public:
     bool hidden() const;
     String visibility_state() const;
 
+    void run_the_resize_steps();
+
 private:
     explicit Document(const AK::URL&);
 
@@ -388,6 +390,9 @@ private:
 
     // https://html.spec.whatwg.org/#page-showing
     bool m_page_showing { false };
+
+    // Used by run_the_resize_steps().
+    Gfx::IntSize m_last_viewport_size;
 };
 
 }

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

@@ -153,7 +153,10 @@ void EventLoop::process()
 
     // FIXME:     6. For each fully active Document in docs, flush autofocus candidates for that Document if its browsing context is a top-level browsing context.
 
-    // FIXME:     7. For each fully active Document in docs, run the resize steps for that Document, passing in now as the timestamp. [CSSOMVIEW]
+    // 7. For each fully active Document in docs, run the resize steps for that Document, passing in now as the timestamp. [CSSOMVIEW]
+    for_each_fully_active_document_in_docs([&](DOM::Document& document) {
+        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]
 

Userland/Libraries/LibWeb/Page/BrowsingContext.cpp

@@ -5,16 +5,15 @@
  */
 
 #include <LibWeb/DOM/Document.h>
-#include <LibWeb/DOM/Event.h>
 #include <LibWeb/DOM/HTMLCollection.h>
 #include <LibWeb/DOM/Window.h>
+#include <LibWeb/HTML/EventLoop/EventLoop.h>
 #include <LibWeb/HTML/HTMLAnchorElement.h>
 #include <LibWeb/Layout/BreakNode.h>
 #include <LibWeb/Layout/InitialContainingBlock.h>
 #include <LibWeb/Layout/TextNode.h>
 #include <LibWeb/Page/BrowsingContext.h>
 #include <LibWeb/Page/Page.h>
-#include <LibWeb/UIEvents/EventNames.h>
 
 namespace Web {
 
@@ -83,10 +82,6 @@ void BrowsingContext::set_viewport_rect(Gfx::IntRect const& rect)
 
     if (m_size != rect.size()) {
         m_size = rect.size();
-        if (active_document()) {
-            active_document()->window().dispatch_event(DOM::Event::create(UIEvents::EventNames::resize));
-            active_document()->update_layout();
-        }
         did_change = true;
     }
 
@@ -99,6 +94,9 @@ void BrowsingContext::set_viewport_rect(Gfx::IntRect const& rect)
         for (auto* client : m_viewport_clients)
             client->browsing_context_did_set_viewport_rect(rect);
     }
+
+    // Schedule the HTML event loop to ensure that a `resize` event gets fired.
+    HTML::main_thread_event_loop().schedule();
 }
 
 void BrowsingContext::set_size(Gfx::IntSize const& size)
@@ -106,13 +104,12 @@ void BrowsingContext::set_size(Gfx::IntSize const& size)
     if (m_size == size)
         return;
     m_size = size;
-    if (active_document()) {
-        active_document()->window().dispatch_event(DOM::Event::create(UIEvents::EventNames::resize));
-        active_document()->update_layout();
-    }
 
     for (auto* client : m_viewport_clients)
         client->browsing_context_did_set_viewport_rect(viewport_rect());
+
+    // Schedule the HTML event loop to ensure that a `resize` event gets fired.
+    HTML::main_thread_event_loop().schedule();
 }
 
 void BrowsingContext::set_viewport_scroll_offset(Gfx::IntPoint const& offset)