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author | Matt A. Tobin <mattatobin@localhost.localdomain> | 2018-02-02 04:16:08 -0500 |
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committer | Matt A. Tobin <mattatobin@localhost.localdomain> | 2018-02-02 04:16:08 -0500 |
commit | 5f8de423f190bbb79a62f804151bc24824fa32d8 (patch) | |
tree | 10027f336435511475e392454359edea8e25895d /gfx/layers/AxisPhysicsMSDModel.cpp | |
parent | 49ee0794b5d912db1f95dce6eb52d781dc210db5 (diff) | |
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Add m-esr52 at 52.6.0
Diffstat (limited to 'gfx/layers/AxisPhysicsMSDModel.cpp')
-rw-r--r-- | gfx/layers/AxisPhysicsMSDModel.cpp | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/gfx/layers/AxisPhysicsMSDModel.cpp b/gfx/layers/AxisPhysicsMSDModel.cpp new file mode 100644 index 000000000..58649cc24 --- /dev/null +++ b/gfx/layers/AxisPhysicsMSDModel.cpp @@ -0,0 +1,93 @@ +/* -*- 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 |