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https://gitlab.winehq.org/wine/wine-gecko.git
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e17dcc92bc
- Implemented the AxisPhysicsModel class, which encapsulates interpolation and integration of a 1-dimensional physics model in a frame-rate independent and stable manner. - Implemented the AxisPhysicsMSDModel class, which models a generic 1-dimensional Mass-Spring-Damper simulation. - This physical movement simulation code has been implemented separately from the existing momentum code in Axis.cpp so that it can be utilized by both the compositor (AsyncPanZoomController) and main thread (nsGfxScrollFrame).
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 -*- */
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/* vim: set sw=2 ts=8 et tw=80 : */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include "AxisPhysicsModel.h"
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namespace mozilla {
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namespace layers {
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/**
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* The simulation is advanced forward in time with a fixed time step to ensure
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* that it remains deterministic given variable framerates. To determine the
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* position at any variable time, two samples are interpolated.
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*
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* kFixedtimestep is set to 120hz in order to ensure that every frame in a
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* common 60hz refresh rate display will have at least one physics simulation
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* sample. More accuracy can be obtained by reducing kFixedTimestep to smaller
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* intervals, such as 240hz or 1000hz, at the cost of more CPU cycles. If
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* kFixedTimestep is increased to much longer intervals, interpolation will
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* become less effective at reducing temporal jitter and the simulation will
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* lose accuracy.
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*/
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const double AxisPhysicsModel::kFixedTimestep = 1.0 / 120.0; // 120hz
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/**
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* Constructs an AxisPhysicsModel with initial values for state.
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*
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* @param aInitialPosition sets the initial position of the simulation,
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* in AppUnits.
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* @param aInitialVelocity sets the initial velocity of the simulation,
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* in AppUnits / second.
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*/
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AxisPhysicsModel::AxisPhysicsModel(double aInitialPosition,
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double aInitialVelocity)
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: mProgress(1.0)
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, mPrevState(aInitialPosition, aInitialVelocity)
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, mNextState(aInitialPosition, aInitialVelocity)
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{
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}
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AxisPhysicsModel::~AxisPhysicsModel()
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{
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}
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double
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AxisPhysicsModel::GetVelocity()
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{
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return LinearInterpolate(mPrevState.v, mNextState.v, mProgress);
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}
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double
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AxisPhysicsModel::GetPosition()
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{
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return LinearInterpolate(mPrevState.p, mNextState.p, mProgress);
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}
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void
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AxisPhysicsModel::SetVelocity(double aVelocity)
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{
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mNextState.v = aVelocity;
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mNextState.p = GetPosition();
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mProgress = 1.0;
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}
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void
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AxisPhysicsModel::SetPosition(double aPosition)
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{
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mNextState.v = GetVelocity();
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mNextState.p = aPosition;
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mProgress = 1.0;
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}
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void
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AxisPhysicsModel::Simulate(const TimeDuration& aDeltaTime)
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{
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for(mProgress += aDeltaTime.ToSeconds() / kFixedTimestep;
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mProgress > 1.0; mProgress -= 1.0) {
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Integrate(kFixedTimestep);
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}
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}
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void
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AxisPhysicsModel::Integrate(double aDeltaTime)
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{
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mPrevState = mNextState;
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// RK4 (Runge-Kutta method) Integration
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// http://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods
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Derivative a = Evaluate( mNextState, 0.0, Derivative() );
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Derivative b = Evaluate( mNextState, aDeltaTime * 0.5, a );
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Derivative c = Evaluate( mNextState, aDeltaTime * 0.5, b );
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Derivative d = Evaluate( mNextState, aDeltaTime, c );
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double dpdt = 1.0 / 6.0 * (a.dp + 2.0 * (b.dp + c.dp) + d.dp);
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double dvdt = 1.0 / 6.0 * (a.dv + 2.0 * (b.dv + c.dv) + d.dv);
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mNextState.p += dpdt * aDeltaTime;
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mNextState.v += dvdt * aDeltaTime;
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}
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AxisPhysicsModel::Derivative
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AxisPhysicsModel::Evaluate(const State &aInitState, double aDeltaTime,
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const Derivative &aDerivative)
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{
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State state( aInitState.p + aDerivative.dp*aDeltaTime, aInitState.v + aDerivative.dv*aDeltaTime );
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return Derivative( state.v, Acceleration(state) );
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}
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double
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AxisPhysicsModel::LinearInterpolate(double aV1, double aV2, double aBlend)
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{
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return aV1 * (1.0 - aBlend) + aV2 * aBlend;
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}
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}
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}
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