1 files changed, 105 insertions, 0 deletions
diff --git a/layout/generic/AsyncScrollBase.h b/layout/generic/AsyncScrollBase.h
new file mode 100644
index 000000000..45e9d3530
--- /dev/null
+++ b/layout/generic/AsyncScrollBase.h
@@ -0,0 +1,105 @@
+/* -*- 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/. */
+
+#ifndef mozilla_layout_AsyncScrollBase_h_
+#define mozilla_layout_AsyncScrollBase_h_
+
+#include "mozilla/TimeStamp.h"
+#include "nsPoint.h"
+#include "nsSMILKeySpline.h"
+
+namespace mozilla {
+
+// This is the base class for driving scroll wheel animation on both the
+// compositor and main thread.
+class AsyncScrollBase
+{
+public:
+  typedef mozilla::TimeStamp TimeStamp;
+  typedef mozilla::TimeDuration TimeDuration;
+
+  explicit AsyncScrollBase(nsPoint aStartPos);
+
+  void Update(TimeStamp aTime,
+              nsPoint aDestination,
+              const nsSize& aCurrentVelocity);
+
+  // Get the velocity at a point in time in nscoords/sec.
+  nsSize VelocityAt(TimeStamp aTime) const;
+
+  // Returns the expected scroll position at a given point in time, in app
+  // units, relative to the scroll frame.
+  nsPoint PositionAt(TimeStamp aTime) const;
+
+  bool IsFinished(TimeStamp aTime) {
+    return aTime > mStartTime + mDuration;
+  }
+
+protected:
+  double ProgressAt(TimeStamp aTime) const {
+    return clamped((aTime - mStartTime) / mDuration, 0.0, 1.0);
+  }
+
+  nscoord VelocityComponent(double aTimeProgress,
+                            const nsSMILKeySpline& aTimingFunction,
+                            nscoord aStart, nscoord aDestination) const;
+
+  // Calculate duration, possibly dynamically according to events rate and
+  // event origin. (also maintain previous timestamps - which are only used
+  // here).
+  TimeDuration ComputeDuration(TimeStamp aTime);
+
+  // Initialize event history.
+  void InitializeHistory(TimeStamp aTime);
+
+  // Initializes the timing function in such a way that the current velocity is
+  // preserved.
+  void InitTimingFunction(nsSMILKeySpline& aTimingFunction,
+                          nscoord aCurrentPos, nscoord aCurrentVelocity,
+                          nscoord aDestination);
+
+  // mPrevEventTime holds previous 3 timestamps for intervals averaging (to
+  // reduce duration fluctuations). When AsyncScroll is constructed and no
+  // previous timestamps are available (indicated with mIsFirstIteration),
+  // initialize mPrevEventTime using imaginary previous timestamps with maximum
+  // relevant intervals between them.
+  TimeStamp mPrevEventTime[3];
+  bool mIsFirstIteration;
+
+  TimeStamp mStartTime;
+
+  // Cached Preferences value.
+  //
+  // These values are minimum and maximum animation duration per event origin,
+  // and a global ratio which defines how longer is the animation's duration
+  // compared to the average recent events intervals (such that for a relatively
+  // consistent events rate, the next event arrives before current animation ends)
+  int32_t mOriginMinMS;
+  int32_t mOriginMaxMS;
+  double mIntervalRatio;
+
+  nsPoint mStartPos;
+  TimeDuration mDuration;
+  nsPoint mDestination;
+  nsSMILKeySpline mTimingFunctionX;
+  nsSMILKeySpline mTimingFunctionY;
+};
+
+// Helper for accelerated wheel deltas. This can be called from the main thread
+// or the APZ Controller thread.
+static inline double
+ComputeAcceleratedWheelDelta(double aDelta, int32_t aCounter, int32_t aFactor)
+{
+  if (!aDelta) {
+    return aDelta;
+  }
+  return (aDelta * aCounter * double(aFactor) / 10);
+}
+
+static const uint32_t kScrollSeriesTimeoutMs = 80; // in milliseconds
+
+} // namespace mozilla
+
+#endif // mozilla_layout_AsyncScrollBase_h_