mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-02 15:15:23 +00:00
a8939590de
The bulk of this commit was generated by running:
run-clang-tidy.py \
-checks='-*,llvm-namespace-comment' \
-header-filter=^/.../mozilla-central/.* \
-fix
122 lines
3.5 KiB
C++
122 lines
3.5 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 "AxisPhysicsModel.h"
|
|
|
|
namespace mozilla {
|
|
namespace layers {
|
|
|
|
/**
|
|
* The simulation is advanced forward in time with a fixed time step to ensure
|
|
* that it remains deterministic given variable framerates. To determine the
|
|
* position at any variable time, two samples are interpolated.
|
|
*
|
|
* kFixedtimestep is set to 120hz in order to ensure that every frame in a
|
|
* common 60hz refresh rate display will have at least one physics simulation
|
|
* sample. More accuracy can be obtained by reducing kFixedTimestep to smaller
|
|
* intervals, such as 240hz or 1000hz, at the cost of more CPU cycles. If
|
|
* kFixedTimestep is increased to much longer intervals, interpolation will
|
|
* become less effective at reducing temporal jitter and the simulation will
|
|
* lose accuracy.
|
|
*/
|
|
const double AxisPhysicsModel::kFixedTimestep = 1.0 / 120.0; // 120hz
|
|
|
|
/**
|
|
* Constructs an AxisPhysicsModel with initial values for state.
|
|
*
|
|
* @param aInitialPosition sets the initial position of the simulation,
|
|
* in AppUnits.
|
|
* @param aInitialVelocity sets the initial velocity of the simulation,
|
|
* in AppUnits / second.
|
|
*/
|
|
AxisPhysicsModel::AxisPhysicsModel(double aInitialPosition,
|
|
double aInitialVelocity)
|
|
: mProgress(1.0)
|
|
, mPrevState(aInitialPosition, aInitialVelocity)
|
|
, mNextState(aInitialPosition, aInitialVelocity)
|
|
{
|
|
|
|
}
|
|
|
|
AxisPhysicsModel::~AxisPhysicsModel()
|
|
{
|
|
|
|
}
|
|
|
|
double
|
|
AxisPhysicsModel::GetVelocity()
|
|
{
|
|
return LinearInterpolate(mPrevState.v, mNextState.v, mProgress);
|
|
}
|
|
|
|
double
|
|
AxisPhysicsModel::GetPosition()
|
|
{
|
|
return LinearInterpolate(mPrevState.p, mNextState.p, mProgress);
|
|
}
|
|
|
|
void
|
|
AxisPhysicsModel::SetVelocity(double aVelocity)
|
|
{
|
|
mNextState.v = aVelocity;
|
|
mNextState.p = GetPosition();
|
|
mProgress = 1.0;
|
|
}
|
|
|
|
void
|
|
AxisPhysicsModel::SetPosition(double aPosition)
|
|
{
|
|
mNextState.v = GetVelocity();
|
|
mNextState.p = aPosition;
|
|
mProgress = 1.0;
|
|
}
|
|
|
|
void
|
|
AxisPhysicsModel::Simulate(const TimeDuration& aDeltaTime)
|
|
{
|
|
for(mProgress += aDeltaTime.ToSeconds() / kFixedTimestep;
|
|
mProgress > 1.0; mProgress -= 1.0) {
|
|
Integrate(kFixedTimestep);
|
|
}
|
|
}
|
|
|
|
void
|
|
AxisPhysicsModel::Integrate(double aDeltaTime)
|
|
{
|
|
mPrevState = mNextState;
|
|
|
|
// RK4 (Runge-Kutta method) Integration
|
|
// http://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods
|
|
Derivative a = Evaluate( mNextState, 0.0, Derivative() );
|
|
Derivative b = Evaluate( mNextState, aDeltaTime * 0.5, a );
|
|
Derivative c = Evaluate( mNextState, aDeltaTime * 0.5, b );
|
|
Derivative d = Evaluate( mNextState, aDeltaTime, c );
|
|
|
|
double dpdt = 1.0 / 6.0 * (a.dp + 2.0 * (b.dp + c.dp) + d.dp);
|
|
double dvdt = 1.0 / 6.0 * (a.dv + 2.0 * (b.dv + c.dv) + d.dv);
|
|
|
|
mNextState.p += dpdt * aDeltaTime;
|
|
mNextState.v += dvdt * aDeltaTime;
|
|
}
|
|
|
|
AxisPhysicsModel::Derivative
|
|
AxisPhysicsModel::Evaluate(const State &aInitState, double aDeltaTime,
|
|
const Derivative &aDerivative)
|
|
{
|
|
State state( aInitState.p + aDerivative.dp*aDeltaTime, aInitState.v + aDerivative.dv*aDeltaTime );
|
|
|
|
return Derivative( state.v, Acceleration(state) );
|
|
}
|
|
|
|
double
|
|
AxisPhysicsModel::LinearInterpolate(double aV1, double aV2, double aBlend)
|
|
{
|
|
return aV1 * (1.0 - aBlend) + aV2 * aBlend;
|
|
}
|
|
|
|
} // namespace layers
|
|
} // namespace mozilla
|