mirror of
https://gitlab.winehq.org/wine/wine-gecko.git
synced 2024-09-13 09:24:08 -07:00
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).
101 lines
3.7 KiB
C++
101 lines
3.7 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()
|
||
{
|
||
return mDestination;
|
||
}
|
||
|
||
void
|
||
AxisPhysicsMSDModel::SetDestination(double aDestination)
|
||
{
|
||
mDestination = aDestination;
|
||
}
|
||
|
||
bool
|
||
AxisPhysicsMSDModel::IsFinished()
|
||
{
|
||
// In order to satisfy the condition of reaching the destination, the distance
|
||
// between the simulation position and the destination must be less than
|
||
// kFinishDistance while the speed is simultaneously less than
|
||
// kFinishVelocity. This enables an under-damped system to overshoot the
|
||
// destination when desired without prematurely triggering the finished state.
|
||
|
||
// As the number of app units per css pixel is 60 and retina / HiDPI displays
|
||
// may display two pixels for every css pixel, setting kFinishDistance to 30.0
|
||
// ensures that there will be no perceptable shift in position at the end
|
||
// of the animation.
|
||
const double kFinishDistance = 30.0;
|
||
|
||
// If kFinishVelocity 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.
|
||
// 60.0 was selected through experimentation that revealed that a
|
||
// critically damped system will terminate within 100ms.
|
||
const double kFinishVelocity = 60.0;
|
||
|
||
return fabs(mDestination - GetPosition ()) < kFinishDistance
|
||
&& fabs(GetVelocity()) <= kFinishVelocity;
|
||
}
|
||
|
||
}
|
||
}
|