LibWeb: Refresh clip and scroll state only when needed

Although refreshing is cheap, it was performed before each hit-testing
and was 2-4% in profiles on Discord and Twitter.

Now clip and scroll states are refreshed only if scroll offset has
changed.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -5056,4 +5056,16 @@ void Document::process_top_layer_removals()
     }
 }
 
+void Document::set_needs_to_refresh_clip_state(bool b)
+{
+    if (auto* paintable = this->paintable())
+        paintable->set_needs_to_refresh_clip_state(b);
+}
+
+void Document::set_needs_to_refresh_scroll_state(bool b)
+{
+    if (auto* paintable = this->paintable())
+        paintable->set_needs_to_refresh_scroll_state(b);
+}
+
 }

Userland/Libraries/LibWeb/DOM/Document.h

@@ -474,6 +474,9 @@ class Document
     bool needs_full_style_update() const { return m_needs_full_style_update; }
     void set_needs_full_style_update(bool b) { m_needs_full_style_update = b; }
 
+    void set_needs_to_refresh_clip_state(bool b);
+    void set_needs_to_refresh_scroll_state(bool b);
+
     bool has_active_favicon() const { return m_active_favicon; }
     void check_favicon_after_loading_link_resource();
 

Userland/Libraries/LibWeb/Painting/PaintableBox.cpp

@@ -71,6 +71,9 @@ void PaintableBox::set_scroll_offset(CSSPixelPoint offset)
     if (!scrollable_overflow_rect.has_value())
         return;
 
+    document().set_needs_to_refresh_clip_state(true);
+    document().set_needs_to_refresh_scroll_state(true);
+
     auto max_x_offset = scrollable_overflow_rect->width() - content_size().width();
     auto max_y_offset = scrollable_overflow_rect->height() - content_size().height();
     offset.set_x(clamp(offset.x(), 0, max_x_offset));

Userland/Libraries/LibWeb/Painting/ViewportPaintable.cpp

@@ -128,6 +128,10 @@ void ViewportPaintable::assign_clip_frames()
 
 void ViewportPaintable::refresh_scroll_state()
 {
+    if (!m_needs_to_refresh_scroll_state)
+        return;
+    m_needs_to_refresh_scroll_state = false;
+
     for (auto& it : scroll_state) {
         auto const& paintable_box = *it.key;
         auto& scroll_frame = *it.value;
@@ -142,6 +146,10 @@ void ViewportPaintable::refresh_scroll_state()
 
 void ViewportPaintable::refresh_clip_state()
 {
+    if (!m_needs_to_refresh_clip_state)
+        return;
+    m_needs_to_refresh_clip_state = false;
+
     for (auto& it : clip_state) {
         auto const& paintable_box = *it.key;
         auto& clip_frame = *it.value;

Userland/Libraries/LibWeb/Painting/ViewportPaintable.h

@@ -36,12 +36,18 @@ class ViewportPaintable final : public PaintableWithLines {
 
     bool handle_mousewheel(Badge<EventHandler>, CSSPixelPoint, unsigned, unsigned, int wheel_delta_x, int wheel_delta_y) override;
 
+    void set_needs_to_refresh_clip_state(bool value) { m_needs_to_refresh_clip_state = value; }
+    void set_needs_to_refresh_scroll_state(bool value) { m_needs_to_refresh_scroll_state = value; }
+
 private:
     void build_stacking_context_tree();
 
     explicit ViewportPaintable(Layout::Viewport const&);
 
     virtual void visit_edges(Visitor&) override;
+
+    bool m_needs_to_refresh_clip_state { true };
+    bool m_needs_to_refresh_scroll_state { true };
 };
 
 }