1 files changed, 45 insertions, 0 deletions
diff --git a/gfx/layers/apz/src/OvershootDetector.h b/gfx/layers/apz/src/OvershootDetector.h
new file mode 100644
index 0000000000..55beee5df2
--- /dev/null
+++ b/gfx/layers/apz/src/OvershootDetector.h
@@ -0,0 +1,45 @@
+/* -*- 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_OvershootDetector_h_
+#define mozilla_layers_OvershootDetector_h_
+
+#include "mozilla/gfx/Types.h"  // for Side
+#include "mozilla/Maybe.h"
+#include "mozilla/TimeStamp.h"
+
+namespace mozilla {
+
+class ScrollWheelInput;
+
+namespace layers {
+
+/*
+ * Handles detection and telemetry reporting of overshoot events, which are
+ * situations where the user changes scrolling direction shortly after a
+ * previous scroll in the other direction, indicating that the user likely
+ * scrolled too far and had to backtrack.
+ *
+ * Currently this data collection is focused on forms of input that trigger
+ * animated rather than instant scrolling. That includes ScrollWheelInput
+ * (currently implemented) and KeyboardInput (planned in bug 1838568).
+ */
+class OvershootDetector {
+ public:
+  OvershootDetector() = default;
+
+  // Updates the internal state machine with a new incoming scrollwheel input.
+  void Update(const ScrollWheelInput& aInput);
+
+ private:
+  TimeStamp mLastTimeStamp;
+  Maybe<mozilla::Side> mLastDirection;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif  // mozilla_layers_OvershootDetector_h_