1 files changed, 60 insertions, 0 deletions
diff --git a/layout/generic/ScrollAnimationPhysics.h b/layout/generic/ScrollAnimationPhysics.h
new file mode 100644
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+++ b/layout/generic/ScrollAnimationPhysics.h
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+/* -*- 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_layout_ScrollAnimationPhysics_h_
+#define mozilla_layout_ScrollAnimationPhysics_h_
+
+#include "mozilla/TimeStamp.h"
+#include "nsPoint.h"
+#include "Units.h"
+
+namespace mozilla {
+
+class ScrollAnimationPhysics {
+ public:
+  // Update the animation to have |aDestination| as its new destination.
+  // The animation's current position remains unchanged, and the shape
+  // of the animation curve is recomputed between the current position
+  // and the new destination.
+  // This is used in cases where an input event that would cause another
+  // animation of this kind is received while this animation is running.
+  virtual void Update(const TimeStamp& aTime, const nsPoint& aDestination,
+                      const nsSize& aCurrentVelocity) = 0;
+
+  // Shift both the current position and the destination of the animation
+  // by |aShiftDelta|. The progress of the animation along its animation
+  // curve is unchanged.
+  // This is used in cases where the main thread changes the scroll offset
+  // (e.g. via scrollBy()) but we want the "momentum" represented by the
+  // animation to be preserved.
+  virtual void ApplyContentShift(const CSSPoint& aShiftDelta) = 0;
+
+  // Get the velocity at a point in time in nscoords/sec.
+  virtual nsSize VelocityAt(const TimeStamp& aTime) = 0;
+
+  // Returns the expected scroll position at a given point in time, in app
+  // units, relative to the scroll frame.
+  virtual nsPoint PositionAt(const TimeStamp& aTime) = 0;
+
+  virtual bool IsFinished(const TimeStamp& aTime) = 0;
+
+  virtual ~ScrollAnimationPhysics() = default;
+};
+
+// 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);
+}
+
+}  // namespace mozilla
+
+#endif  // mozilla_layout_ScrollAnimationPhysics_h_