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518693048f
- 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).
132 lines
3.3 KiB
C++
132 lines
3.3 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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#ifndef mozilla_layers_AxisPhysicsModel_h
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#define mozilla_layers_AxisPhysicsModel_h
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#include "AxisPhysicsModel.h"
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#include <sys/types.h> // for int32_t
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#include "mozilla/TimeStamp.h" // for TimeDuration
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namespace mozilla {
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namespace layers {
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/**
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* AxisPhysicsModel encapsulates a generic 1-dimensional physically-based motion
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* model.
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*
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* It performs frame-rate independent interpolation and RK4 integration for
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* smooth animation with stable, deterministic behavior.
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* Implementations are expected to subclass and override the Acceleration()
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* method.
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*/
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class AxisPhysicsModel {
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public:
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AxisPhysicsModel(double aInitialPosition, double aInitialVelocity);
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~AxisPhysicsModel();
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/**
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* Advance the physics simulation.
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* |aDelta| is the time since the last sample.
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*/
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void Simulate(const TimeDuration& aDeltaTime);
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/**
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* Gets the raw velocity of this axis at this moment.
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*/
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double GetVelocity();
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/**
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* Sets the raw velocity of this axis at this moment.
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*/
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void SetVelocity(double aVelocity);
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/**
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* Gets the raw position of this axis at this moment.
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*/
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double GetPosition();
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/**
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* Sets the raw position of this axis at this moment.
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*/
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void SetPosition(double aPosition);
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protected:
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struct State
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{
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State(double ap, double av) : p(ap), v(av) {};
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double p; // Position
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double v; // Velocity
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};
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struct Derivative
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{
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Derivative() : dp(0.0), dv(0.0) {};
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Derivative(double aDp, double aDv) : dp(aDp), dv(aDv) {};
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double dp; // dp / delta time = Position
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double dv; // dv / delta time = Velocity
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};
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/**
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* Acceleration must be overridden and return the number of
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* axis-position-units / second that should be added or removed from the
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* velocity.
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*/
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virtual double Acceleration(const State &aState) = 0;
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private:
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/**
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* Duration of fixed delta time step (seconds)
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*/
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static const double kFixedTimestep;
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/**
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* 0.0 - 1.0 value indicating progress between current and next simulation
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* sample. Normalized to units of kFixedTimestep duration.
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*/
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double mProgress;
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/**
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* Sample of simulation state as it existed
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* (1.0 - mProgress) * kFixedTimestep seconds in the past.
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*/
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State mPrevState;
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/**
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* Sample of simulation state as it will be in mProgress * kFixedTimestep
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* seconds in the future.
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*/
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State mNextState;
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/**
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* Perform RK4 (Runge-Kutta method) Integration to calculate the next
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* simulation sample.
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*/
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void Integrate(double aDeltaTime);
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/**
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* Apply delta velocity and position represented by aDerivative over
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* aDeltaTime seconds, calculate new acceleration, and return new deltas.
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*/
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Derivative Evaluate(const State &aInitState, double aDeltaTime,
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const Derivative &aDerivative);
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/**
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* Helper function for performing linear interpolation (lerp) of double's
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*/
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static double LinearInterpolate(double aV1, double aV2, double aBlend);
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};
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}
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}
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#endif
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