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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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diff --git a/gfx/layers/AxisPhysicsMSDModel.cpp b/gfx/layers/AxisPhysicsMSDModel.cpp
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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/. */
+
+#include "AxisPhysicsMSDModel.h"
+#include <math.h> // for sqrt and fabs
+
+namespace mozilla {
+namespace layers {
+
+/**
+ * Constructs an AxisPhysicsMSDModel with initial values for state.
+ *
+ * @param aInitialPosition sets the initial position of the simulated spring,
+ * in AppUnits.
+ * @param aInitialDestination sets the resting position of the simulated spring,
+ * in AppUnits.
+ * @param aInitialVelocity sets the initial velocity of the simulated spring,
+ * in AppUnits / second. Critically-damped and over-damped systems are
+ * guaranteed not to overshoot aInitialDestination if this is set to 0;
+ * however, it is possible to overshoot and oscillate if not set to 0 or
+ * the system is under-damped.
+ * @param aSpringConstant sets the strength of the simulated spring. Greater
+ * values of mSpringConstant result in a stiffer / stronger spring.
+ * @param aDampingRatio controls the amount of dampening force and determines
+ * if the system is under-damped, critically-damped, or over-damped.
+ */
+AxisPhysicsMSDModel::AxisPhysicsMSDModel(double aInitialPosition,
+ double aInitialDestination,
+ double aInitialVelocity,
+ double aSpringConstant,
+ double aDampingRatio)
+ : AxisPhysicsModel(aInitialPosition, aInitialVelocity)
+ , mDestination(aInitialDestination)
+ , mSpringConstant(aSpringConstant)
+ , mSpringConstantSqrtXTwo(sqrt(mSpringConstant) * 2.0)
+ , mDampingRatio(aDampingRatio)
+{
+}
+
+AxisPhysicsMSDModel::~AxisPhysicsMSDModel()
+{
+}
+
+double
+AxisPhysicsMSDModel::Acceleration(const State &aState)
+{
+ // Simulate a Mass-Damper-Spring Model; assume a unit mass
+
+ // Hooke’s Law: http://en.wikipedia.org/wiki/Hooke%27s_law
+ double spring_force = (mDestination - aState.p) * mSpringConstant;
+ double damp_force = -aState.v * mDampingRatio * mSpringConstantSqrtXTwo;
+
+ return spring_force + damp_force;
+}
+
+
+double
+AxisPhysicsMSDModel::GetDestination() const
+{
+ return mDestination;
+}
+
+void
+AxisPhysicsMSDModel::SetDestination(double aDestination)
+{
+ mDestination = aDestination;
+}
+
+bool
+AxisPhysicsMSDModel::IsFinished(double aSmallestVisibleIncrement)
+{
+ // In order to satisfy the condition of reaching the destination, the distance
+ // between the simulation position and the destination must be less than
+ // aSmallestVisibleIncrement while the speed is simultaneously less than
+ // finishVelocity. This enables an under-damped system to overshoot the
+ // destination when desired without prematurely triggering the finished state.
+ // If finishVelocity is set too low, the animation may end long after
+ // oscillation has finished, resulting in unnecessary processing.
+ // If set too high, the animation may prematurely terminate when expected
+ // to overshoot the destination in an under-damped system.
+ // aSmallestVisibleIncrement * 2 was selected through experimentation that
+ // revealed that a critically damped system will terminate within 100ms.
+ const double finishVelocity = aSmallestVisibleIncrement * 2;
+
+ return fabs(mDestination - GetPosition ()) < aSmallestVisibleIncrement
+ && fabs(GetVelocity()) <= finishVelocity;
+}
+
+} // namespace layers
+} // namespace mozilla