LibWeb: Transition StyleComputer to Web Animations

With this commit, we are finally running animations off of the web
animations spec! A lot of the work StyleComputer is doing is now done
elsewhere. For example, fill-forward animations are handled by
Animation::is_relevant() returning true in the after phase, meaning the
"active_state_if_fill_forward" map is no longer needed.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -23,6 +23,8 @@
 #include <LibWeb/Animations/AnimationTimeline.h>
 #include <LibWeb/Animations/DocumentTimeline.h>
 #include <LibWeb/Bindings/MainThreadVM.h>
+#include <LibWeb/CSS/AnimationEvent.h>
+#include <LibWeb/CSS/CSSAnimation.h>
 #include <LibWeb/CSS/MediaQueryList.h>
 #include <LibWeb/CSS/MediaQueryListEvent.h>
 #include <LibWeb/CSS/StyleComputer.h>
@@ -1889,6 +1891,19 @@ Element* Document::find_a_potential_indicated_element(FlyString const& fragment)
     return nullptr;
 }
 
+// https://www.w3.org/TR/css-animations-2/#event-dispatch
+void Document::dispatch_events_for_animation_if_necessary(JS::NonnullGCPtr<Animations::Animation> animation)
+{
+    // Each time a new animation frame is established and the animation does not have a pending play task or pending
+    // pause task, the events to dispatch are determined by comparing the animation’s phase before and after
+    // establishing the new animation frame as follows:
+    auto effect = animation->effect();
+    if (!effect || !effect->is_keyframe_effect() || !animation->is_css_animation() || animation->pending())
+        return;
+
+    // TODO: Dispatch events
+}
+
 // https://html.spec.whatwg.org/multipage/browsing-the-web.html#scroll-to-the-fragment-identifier
 void Document::scroll_to_the_fragment()
 {
@@ -3908,6 +3923,35 @@ void Document::remove_replaced_animations()
     }
 }
 
+void Document::ensure_animation_timer()
+{
+    constexpr static auto timer_delay_ms = 1000 / 60;
+    if (!m_animation_driver_timer) {
+        m_animation_driver_timer = Platform::Timer::create_repeating(timer_delay_ms, [this] {
+            bool has_animations = false;
+            for (auto& timeline : m_associated_animation_timelines) {
+                if (!timeline->associated_animations().is_empty()) {
+                    has_animations = true;
+                    break;
+                }
+            }
+            if (!has_animations) {
+                m_animation_driver_timer->stop();
+                return;
+            }
+
+            update_animations_and_send_events(MonotonicTime::now().milliseconds());
+
+            for (auto& timeline : m_associated_animation_timelines) {
+                for (auto& animation : timeline->associated_animations())
+                    dispatch_events_for_animation_if_necessary(animation);
+            }
+        });
+    }
+
+    m_animation_driver_timer->start();
+}
+
 // https://html.spec.whatwg.org/multipage/dom.html#dom-document-nameditem-filter
 static bool is_potentially_named_element(DOM::Element const& element)
 {

Userland/Libraries/LibWeb/DOM/Document.h

@@ -561,6 +561,7 @@ public:
     void append_pending_animation_event(PendingAnimationEvent const&);
     void update_animations_and_send_events(Optional<double> const& timestamp);
     void remove_replaced_animations();
+    void ensure_animation_timer();
 
     bool ready_to_run_scripts() const { return m_ready_to_run_scripts; }
 
@@ -620,6 +621,8 @@ private:
 
     Element* find_a_potential_indicated_element(FlyString const& fragment) const;
 
+    void dispatch_events_for_animation_if_necessary(JS::NonnullGCPtr<Animations::Animation>);
+
     JS::NonnullGCPtr<Page> m_page;
     OwnPtr<CSS::StyleComputer> m_style_computer;
     JS::GCPtr<CSS::StyleSheetList> m_style_sheets;
@@ -815,6 +818,7 @@ private:
 
     // https://www.w3.org/TR/web-animations-1/#pending-animation-event-queue
     Vector<PendingAnimationEvent> m_pending_animation_event_queue;
+    RefPtr<Platform::Timer> m_animation_driver_timer;
 
     bool m_needs_to_call_page_did_load { false };