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authorMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
committerMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
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Add m-esr52 at 52.6.0
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+/* -*- 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