1 files changed, 48 insertions, 0 deletions
diff --git a/dom/animation/ScrollTimelineAnimationTracker.cpp b/dom/animation/ScrollTimelineAnimationTracker.cpp
new file mode 100644
index 0000000000..48cad8cedd
--- /dev/null
+++ b/dom/animation/ScrollTimelineAnimationTracker.cpp
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ScrollTimelineAnimationTracker.h"
+
+#include "mozilla/dom/Document.h"
+
+namespace mozilla {
+
+NS_IMPL_CYCLE_COLLECTION(ScrollTimelineAnimationTracker, mPendingSet, mDocument)
+
+void ScrollTimelineAnimationTracker::TriggerPendingAnimations() {
+  for (auto iter = mPendingSet.begin(), end = mPendingSet.end(); iter != end;
+       ++iter) {
+    dom::Animation* animation = *iter;
+
+    MOZ_ASSERT(animation->GetTimeline() &&
+               !animation->GetTimeline()->IsMonotonicallyIncreasing());
+
+    // FIXME: Trigger now may not be correct because the spec says:
+    // If a user agent determines that animation is immediately ready, it may
+    // schedule the task (i.e. ResumeAt()) as a microtask such that it runs at
+    // the next microtask checkpoint, but it must not perform the task
+    // synchronously.
+    // Note: So, for now, we put the animation into the tracker, and trigger
+    // them immediately until the frames are ready. Using TriggerOnNextTick()
+    // for scroll-driven animations may have issues because we don't tick if
+    // no one does scroll.
+    if (!animation->TryTriggerNow()) {
+      // Note: We keep this animation pending even if its timeline is always
+      // inactive. It's pretty hard to tell its future status, for example, it's
+      // possible that the scroll container is in display:none subtree but the
+      // animating element isn't the subtree, then we need to keep tracking the
+      // situation until the scroll container gets framed. so in general we make
+      // this animation be pending (i.e. not ready) if its scroll-timeline is
+      // inactive, and this also matches the current spec definition.
+      continue;
+    }
+
+    // Note: Remove() is legitimately called once per entry during the loop.
+    mPendingSet.Remove(iter);
+  }
+}
+
+}  // namespace mozilla