mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-06 17:16:12 +00:00
460fb32c11
MozReview-Commit-ID: EUyGvkoyu8I --HG-- extra : rebase_source : b9f9bbb7a11a976ff696c28b026d292a8f90d0e1
94 lines
3.6 KiB
C++
94 lines
3.6 KiB
C++
/* -*- 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
|