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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).
87 lines
2.2 KiB
C++
87 lines
2.2 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_AxisPhysicsMSDModel_h
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#define mozilla_layers_AxisPhysicsMSDModel_h
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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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* AxisPhysicsMSDModel encapsulates a 1-dimensional MSD (Mass-Spring-Damper)
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* model. A unit mass is assumed.
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*/
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class AxisPhysicsMSDModel : public AxisPhysicsModel {
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public:
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AxisPhysicsMSDModel(double aInitialPosition, double aInitialDestination,
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double aInitialVelocity, double aSpringConstant,
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double aDampingRatio);
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~AxisPhysicsMSDModel();
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/**
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* Gets the raw destination of this axis at this moment.
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*/
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double GetDestination();
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/**
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* Sets the raw destination of this axis at this moment.
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*/
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void SetDestination(double aDestination);
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/**
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* Returns true when the position is close to the destination and the
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* velocity is low.
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*/
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bool IsFinished();
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protected:
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virtual double Acceleration(const State &aState);
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private:
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/**
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* mDestination represents the target position and the resting position of
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* the simulated spring.
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*/
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double mDestination;
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/**
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* Greater values of mSpringConstant result in a stiffer / stronger spring.
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*/
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double mSpringConstant;
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/**
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* mSpringConstantSqrtTimesTwo is calculated from mSpringConstant to reduce
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* calculations performed in the inner loop.
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*/
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double mSpringConstantSqrtXTwo;
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/**
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* Damping Ratio: http://en.wikipedia.org/wiki/Damping_ratio
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*
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* When mDampingRatio < 1.0, this is an under damped system.
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* - Overshoots destination and oscillates with the amplitude gradually
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* decreasing to zero.
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*
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* When mDampingRatio == 1.0, this is a critically damped system.
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* - Reaches destination as quickly as possible without oscillating.
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*
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* When mDampingRatio > 1.0, this is an over damped system.
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* - Reaches destination (exponentially decays) without oscillating.
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*/
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double mDampingRatio;
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};
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}
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}
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#endif
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