1 files changed, 49 insertions, 0 deletions
diff --git a/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp b/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp
new file mode 100644
index 000000000..758b705a3
--- /dev/null
+++ b/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp
@@ -0,0 +1,49 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "ScrollLinkedEffectDetector.h"
+
+#include "nsIDocument.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+namespace layers {
+
+uint32_t ScrollLinkedEffectDetector::sDepth = 0;
+bool ScrollLinkedEffectDetector::sFoundScrollLinkedEffect = false;
+
+/* static */ void
+ScrollLinkedEffectDetector::PositioningPropertyMutated()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (sDepth > 0) {
+    // We are inside a scroll event dispatch
+    sFoundScrollLinkedEffect = true;
+  }
+}
+
+ScrollLinkedEffectDetector::ScrollLinkedEffectDetector(nsIDocument* aDoc)
+  : mDocument(aDoc)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  sDepth++;
+}
+
+ScrollLinkedEffectDetector::~ScrollLinkedEffectDetector()
+{
+  sDepth--;
+  if (sDepth == 0) {
+    // We have exited all (possibly-nested) scroll event dispatches,
+    // record whether or not we found an effect, and reset state
+    if (sFoundScrollLinkedEffect) {
+      mDocument->ReportHasScrollLinkedEffect();
+      sFoundScrollLinkedEffect = false;
+    }
+  }
+}
+
+} // namespace layers
+} // namespace mozilla