1 files changed, 83 insertions, 0 deletions
diff --git a/gfx/layers/apz/src/RecentEventsBuffer.h b/gfx/layers/apz/src/RecentEventsBuffer.h
new file mode 100644
index 0000000000..d1ae5797af
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+++ b/gfx/layers/apz/src/RecentEventsBuffer.h
@@ -0,0 +1,83 @@
+/* -*- 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/. */
+
+#ifndef mozilla_layers_RecentEventsBuffer_h
+#define mozilla_layers_RecentEventsBuffer_h
+
+#include <deque>
+
+#include "mozilla/TimeStamp.h"
+
+namespace mozilla {
+namespace layers {
+/**
+ * RecentEventsBuffer: maintains an age constrained buffer of events
+ *
+ * Intended for use with elements of type InputData, but the only requirement
+ * is a member "mTimeStamp" of type TimeStamp
+ */
+template <typename Event>
+class RecentEventsBuffer {
+ public:
+  explicit RecentEventsBuffer(TimeDuration maxAge);
+
+  void push(Event event);
+  void clear();
+
+  typedef typename std::deque<Event>::size_type size_type;
+  size_type size() { return mBuffer.size(); }
+
+  // Delegate to container for iterators
+  typedef typename std::deque<Event>::iterator iterator;
+  typedef typename std::deque<Event>::const_iterator const_iterator;
+  iterator begin() { return mBuffer.begin(); }
+  iterator end() { return mBuffer.end(); }
+  const_iterator cbegin() const { return mBuffer.cbegin(); }
+  const_iterator cend() const { return mBuffer.cend(); }
+
+  // Also delegate for front/back
+  typedef typename std::deque<Event>::reference reference;
+  typedef typename std::deque<Event>::const_reference const_reference;
+  reference front() { return mBuffer.front(); }
+  reference back() { return mBuffer.back(); }
+  const_reference front() const { return mBuffer.front(); }
+  const_reference back() const { return mBuffer.back(); }
+
+ private:
+  TimeDuration mMaxAge;
+  std::deque<Event> mBuffer;
+};
+
+template <typename Event>
+RecentEventsBuffer<Event>::RecentEventsBuffer(TimeDuration maxAge)
+    : mMaxAge(maxAge), mBuffer() {}
+
+template <typename Event>
+void RecentEventsBuffer<Event>::push(Event event) {
+  // Events must be pushed in chronological order
+  MOZ_ASSERT(mBuffer.empty() || mBuffer.back().mTimeStamp <= event.mTimeStamp);
+
+  mBuffer.push_back(event);
+
+  // Flush all events older than the given lifetime
+  TimeStamp bound = event.mTimeStamp - mMaxAge;
+  while (!mBuffer.empty()) {
+    if (mBuffer.front().mTimeStamp >= bound) {
+      break;
+    }
+    mBuffer.pop_front();
+  }
+}
+
+template <typename Event>
+void RecentEventsBuffer<Event>::clear() {
+  mBuffer.clear();
+}
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif  // mozilla_layers_RecentEventsBuffer_h