SpringSettings Class Reference

Settings for a linear or angular spring. More...

#include <SpringSettings.h>

Public Member Functions
	SpringSettings ()=default
	Constructor.
	SpringSettings (const SpringSettings &)=default
SpringSettings &	operator= (const SpringSettings &)=default
	SpringSettings (ESpringMode inMode, float inFrequencyOrStiffness, float inDamping)
void	SaveBinaryState (StreamOut &inStream) const
	Saves the contents of the spring settings in binary form to inStream.
void	RestoreBinaryState (StreamIn &inStream)
	Restores contents from the binary stream inStream.
bool	HasStiffness () const
	Check if the spring has a valid frequency / stiffness, if not the spring will be hard.
bool	HasStiffnessOrDamping () const
	Check if this spring has stiffness or damping (making it active), if not the constraint will be hard.

Public Attributes
ESpringMode	mMode = ESpringMode::FrequencyAndDamping
	Selects the way in which the spring is defined. See the descriptions of the mFrequency, mStiffness and mDamping properties.
union {
float   mFrequency = 0.0f
float   mStiffness
};
float	mDamping = 0.0f

Detailed Description

Settings for a linear or angular spring.

Constructor & Destructor Documentation

SpringSettings() [1/3]

SpringSettings::SpringSettings ( )

default

Constructor.

SpringSettings() [2/3]

SpringSettings::SpringSettings ( const SpringSettings & )

default

SpringSettings() [3/3]

SpringSettings::SpringSettings ( ESpringMode inMode, float inFrequencyOrStiffness, float inDamping )

inline

Member Function Documentation

HasStiffness()

bool SpringSettings::HasStiffness ( ) const

inline

Check if the spring has a valid frequency / stiffness, if not the spring will be hard.

HasStiffnessOrDamping()

bool SpringSettings::HasStiffnessOrDamping ( ) const

inline

Check if this spring has stiffness or damping (making it active), if not the constraint will be hard.

operator=()

SpringSettings & SpringSettings::operator= ( const SpringSettings & )

default

RestoreBinaryState()

void SpringSettings::RestoreBinaryState

(

StreamIn &

inStream

)

Restores contents from the binary stream inStream.

SaveBinaryState()

void SpringSettings::SaveBinaryState

(

StreamOut &

inStream

)

const

Saves the contents of the spring settings in binary form to inStream.

Member Data Documentation

[union]

union { ... } SpringSettings

mDamping

float SpringSettings::mDamping = 0.0f

When mMode = ESpringMode::FrequencyAndDamping this is the damping ratio (0 = no damping, 1 = critical damping).

When mMode = ESpringMode::StiffnessAndDamping this is the damping (c) in the spring equation F = -k * x - c * v for a linear or T = -k * theta - c * w for an angular spring. Units are N s / m for a linear spring and N s m / rad for an angular spring.

When mMode = ESpringMode::MassNormalizedStiffnessAndDamping this is the damping (c) in the spring equation F = m_eff * (-k * x - c * v) for a linear or T = i_eff * (-k * theta - c * w) for an angular spring. m_eff / i_eff is the effective mass / inertia of the constraint. Units are 1 / s for a linear spring and 1 / rad s for an angular spring.

Note that if you set this to 0, you will not get an infinite oscillation. Because we integrate physics using an explicit Euler scheme, there is always energy loss. This is done to keep the simulation from exploding, because with a damping of 0 and even the slightest rounding error, the oscillation could become bigger and bigger until the simulation explodes.

mFrequency

float SpringSettings::mFrequency = 0.0f

Valid when mMode = ESpringMode::FrequencyAndDamping. If > 0 the constraint will be soft and this specifies the oscillation frequency in Hz. If <= 0, mDamping is ignored and the constraint will have hard limits (as hard as the time step / the number of velocity / position solver steps allows).

mMode

ESpringMode SpringSettings::mMode = ESpringMode::FrequencyAndDamping

Selects the way in which the spring is defined. See the descriptions of the mFrequency, mStiffness and mDamping properties.

mStiffness

float SpringSettings::mStiffness

When mMode = ESpringMode::StiffnessAndDamping: Specifies the stiffness (k) in the spring equation F = -k * x - c * v for a linear or T = -k * theta - c * w for an angular spring. Units are N / m for a linear spring and N m / rad for an angular spring.

Note that stiffness values are large numbers. To calculate a ballpark value for the needed stiffness you can use: force = stiffness * delta_spring_length = mass * gravity <=> stiffness = mass * gravity / delta_spring_length. So if your object weighs 1500 kg and the spring compresses by 2 meters, you need a stiffness in the order of 1500 * 9.81 / 2 ~ 7500 N/m.

When mMode = ESpringMode::MassNormalizedStiffnessAndDamping: Specifies the stiffness (k) in the spring equation F = m_eff * (-k * x - c * v) for a linear or T = i_eff * (-k * theta - c * w) for an angular spring. m_eff / i_eff is the effective mass / inertia of the constraint. Units are 1 / s^2 for a linear spring and 1 / rad s^2 for an angular spring.

Since the stiffness is multiplied by the effective mass / inertia of the constraint, you can use much smaller stiffness values and they will be mass independent.

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The documentation for this class was generated from the following files:

• Jolt/Physics/Constraints/SpringSettings.h
• Jolt/Physics/Constraints/SpringSettings.cpp