LibWeb: Fix infinite repaint loop when cached display list is used

Before this change, `m_needs_repaint` was reset in
`Document::record_display_list()` only when the cached display list was
absent. This meant that if the last triggered repaint used the cached
display list, we would keep repainting indefinitely until the display
list was invalidated (We schedule a task that checks if repainting is
required 60/s).

This change also moves `m_needs_repaint` from Document to
TraversableNavigable as we only ever need to repaint a document that
belongs to traversable.

Libraries/LibWeb/DOM/Document.cpp

@@ -6093,8 +6093,6 @@ void Document::set_needs_display(CSSPixelRect const&, InvalidateDisplayList shou
     // FIXME: Ignore updates outside the visible viewport rect.
     //        This requires accounting for fixed-position elements in the input rect, which we don't do yet.
 
-    m_needs_repaint = true;
-
     if (should_invalidate_display_list == InvalidateDisplayList::Yes) {
         invalidate_display_list();
     }
@@ -6104,6 +6102,7 @@ void Document::set_needs_display(CSSPixelRect const&, InvalidateDisplayList shou
         return;
 
     if (navigable->is_traversable()) {
+        navigable->traversable_navigable()->set_needs_repaint();
         Web::HTML::main_thread_event_loop().schedule();
         return;
     }
@@ -6188,8 +6187,6 @@ RefPtr<Painting::DisplayList> Document::record_display_list(PaintConfig config)
     display_list->set_device_pixels_per_css_pixel(page().client().device_pixels_per_css_pixel());
     display_list->set_scroll_state(viewport_paintable.scroll_state());
 
-    m_needs_repaint = false;
-
     m_cached_display_list = display_list;
     m_cached_display_list_paint_config = config;
 

Libraries/LibWeb/DOM/Document.h

@@ -735,7 +735,6 @@ public:
     GC::Ptr<HTML::Navigable> cached_navigable();
     void set_cached_navigable(GC::Ptr<HTML::Navigable>);
 
-    [[nodiscard]] bool needs_repaint() const { return m_needs_repaint; }
     void set_needs_display(InvalidateDisplayList = InvalidateDisplayList::Yes);
     void set_needs_display(CSSPixelRect const&, InvalidateDisplayList = InvalidateDisplayList::Yes);
 
@@ -1101,8 +1100,6 @@ private:
     // NOTE: This is WeakPtr, not GCPtr, on purpose. We don't want the document to keep some old detached navigable alive.
     WeakPtr<HTML::Navigable> m_cached_navigable;
 
-    bool m_needs_repaint { false };
-
     bool m_enable_cookies_on_file_domains { false };
 
     Optional<PaintConfig> m_cached_display_list_paint_config;

Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp

@@ -411,13 +411,13 @@ void EventLoop::update_the_rendering()
     for (auto& document : docs) {
         document->page().client().process_screenshot_requests();
         auto navigable = document->navigable();
-        if (navigable && document->needs_repaint()) {
-            auto* browsing_context = document->browsing_context();
-            auto& page = browsing_context->page();
-            if (navigable->is_traversable()) {
-                VERIFY(page.client().is_ready_to_paint());
-                page.client().paint_next_frame();
-            }
+        if (!navigable->is_traversable())
+            continue;
+        auto traversable = navigable->traversable_navigable();
+        if (traversable && traversable->needs_repaint()) {
+            auto& page = traversable->page();
+            VERIFY(page.client().is_ready_to_paint());
+            page.client().paint_next_frame();
         }
     }
 

Libraries/LibWeb/HTML/Navigable.cpp

@@ -2198,13 +2198,6 @@ void Navigable::perform_scroll_of_viewport(CSSPixelPoint new_position)
     HTML::main_thread_event_loop().schedule();
 }
 
-void Navigable::set_needs_display(InvalidateDisplayList should_invalidate_display_list)
-{
-    if (auto document = active_document(); document) {
-        document->set_needs_display(should_invalidate_display_list);
-    }
-}
-
 // https://html.spec.whatwg.org/#rendering-opportunity
 bool Navigable::has_a_rendering_opportunity() const
 {

Libraries/LibWeb/HTML/Navigable.h

@@ -173,8 +173,6 @@ public:
     virtual void set_viewport_size(CSSPixelSize);
     void perform_scroll_of_viewport(CSSPixelPoint position);
 
-    void set_needs_display(InvalidateDisplayList = InvalidateDisplayList::Yes);
-
     // https://html.spec.whatwg.org/#rendering-opportunity
     [[nodiscard]] bool has_a_rendering_opportunity() const;
 

Libraries/LibWeb/HTML/TraversableNavigable.cpp

@@ -1429,6 +1429,8 @@ NonnullRefPtr<Gfx::PaintingSurface> TraversableNavigable::painting_surface_for_b
 
 void TraversableNavigable::paint(DevicePixelRect const& content_rect, Painting::BackingStore& target, PaintOptions paint_options)
 {
+    m_needs_repaint = false;
+
     auto document = active_document();
     if (!document)
         return;

Libraries/LibWeb/HTML/TraversableNavigable.h

@@ -113,6 +113,9 @@ public:
 
     void set_viewport_size(CSSPixelSize) override;
 
+    bool needs_repaint() const { return m_needs_repaint; }
+    void set_needs_repaint() { m_needs_repaint = true; }
+
 private:
     TraversableNavigable(GC::Ref<Page>);
 
@@ -161,6 +164,8 @@ private:
     RefPtr<Gfx::SkiaBackendContext> m_skia_backend_context;
     OwnPtr<Painting::DisplayListPlayerSkia> m_skia_player;
     HashMap<Gfx::Bitmap*, NonnullRefPtr<Gfx::PaintingSurface>> m_bitmap_to_surface;
+
+    bool m_needs_repaint { true };
 };
 
 struct BrowsingContextAndDocument {

Services/WebContent/ConnectionFromClient.cpp

@@ -374,7 +374,7 @@ void ConnectionFromClient::debug_request(u64 page_id, ByteString const& request,
     if (request == "set-line-box-borders") {
         bool state = argument == "on";
         page->set_should_show_line_box_borders(state);
-        page->page().top_level_traversable()->set_needs_display();
+        page->page().top_level_traversable()->set_needs_repaint();
         return;
     }
 

Services/WebContent/PageClient.cpp

@@ -879,6 +879,6 @@ Web::DisplayListPlayerType PageClient::display_list_player_type() const
 void PageClient::queue_screenshot_task(Optional<Web::UniqueNodeID> node_id)
 {
     m_screenshot_tasks.enqueue({ node_id });
-    page().top_level_traversable()->set_needs_display();
+    page().top_level_traversable()->set_needs_repaint();
 }
 }