import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

gfx/layers/AxisPhysicsMSDModel.h

@@ -0,0 +1,86 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set sw=2 ts=8 et 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_AxisPhysicsMSDModel_h
+#define mozilla_layers_AxisPhysicsMSDModel_h
+
+#include "AxisPhysicsModel.h"
+
+namespace mozilla {
+namespace layers {
+
+/**
+ * AxisPhysicsMSDModel encapsulates a 1-dimensional MSD (Mass-Spring-Damper)
+ * model.  A unit mass is assumed.
+ */
+class AxisPhysicsMSDModel : public AxisPhysicsModel {
+public:
+  AxisPhysicsMSDModel(double aInitialPosition, double aInitialDestination,
+                      double aInitialVelocity, double aSpringConstant,
+                      double aDampingRatio);
+
+  ~AxisPhysicsMSDModel();
+
+  /**
+   * Gets the raw destination of this axis at this moment.
+   */
+  double GetDestination() const;
+
+  /**
+   * Sets the raw destination of this axis at this moment.
+   */
+  void SetDestination(double aDestination);
+
+  /**
+   * Returns true when the position is close to the destination and the
+   * velocity is low.
+   */
+  bool IsFinished(double aSmallestVisibleIncrement);
+
+protected:
+  virtual double Acceleration(const State &aState);
+
+private:
+
+  /**
+   * mDestination represents the target position and the resting position of
+   * the simulated spring.
+   */
+  double mDestination;
+
+  /**
+   * Greater values of mSpringConstant result in a stiffer / stronger spring.
+   */
+  double mSpringConstant;
+
+  /**
+   * mSpringConstantSqrtTimesTwo is calculated from mSpringConstant to reduce
+   * calculations performed in the inner loop.
+   */
+  double mSpringConstantSqrtXTwo;
+
+  /**
+   * Damping Ratio: http://en.wikipedia.org/wiki/Damping_ratio
+   *
+   * When mDampingRatio < 1.0, this is an under damped system.
+   * - Overshoots destination and oscillates with the amplitude gradually
+   *   decreasing to zero.
+   *
+   * When mDampingRatio == 1.0, this is a critically damped system.
+   * - Reaches destination as quickly as possible without oscillating.
+   *
+   * When mDampingRatio > 1.0, this is an over damped system.
+   * - Reaches destination (exponentially decays) without oscillating.
+   */
+  double mDampingRatio;
+
+};
+
+
+} // namespace layers
+} // namespace mozilla
+
+#endif