#include <tgBulletCompressionSpring.h>

Inheritance diagram for tgBulletCompressionSpring:

Collaboration diagram for tgBulletCompressionSpring:

Public Member Functions
	tgBulletCompressionSpring (const std::vector< tgBulletSpringCableAnchor * > &anchors, bool isFreeEndAttached, double coefK, double coefD, double restLength)

virtual	~tgBulletCompressionSpring ()

virtual void	step (double dt)

virtual const double	getCurrentAnchorDistance () const

virtual const double	getCurrentSpringLength () const

virtual const btVector3	getAnchorDirectionUnitVector () const

virtual const btVector3	getSpringEndpoint () const

virtual const double	getSpringForce () const

virtual const double	getCoefK () const

virtual const double	getCoefD () const

virtual const double	getVelocity () const

virtual const double	getDampingForce () const

virtual const double	getRestLength () const

virtual const bool	isFreeEndAttached () const

virtual const std::vector < const tgSpringCableAnchor * >	getAnchors () const

Protected Member Functions
virtual void	calculateAndApplyForce (double dt)

Protected Attributes
std::vector < tgBulletSpringCableAnchor * >	m_anchors

tgBulletSpringCableAnchor *const	anchor1

tgBulletSpringCableAnchor *const	anchor2

double	m_dampingForce

double	m_velocity

bool	m_isFreeEndAttached

const double	m_coefK

const double	m_coefD

double	m_restLength

double	m_prevLength

Detailed Description

This class defines the passive dynamics of a compression spring system, with damping, in the Bullet physics engine.

Definition at line 48 of file tgBulletCompressionSpring.h.

Constructor & Destructor Documentation

tgBulletCompressionSpring::tgBulletCompressionSpring	(	const std::vector< tgBulletSpringCableAnchor * > &	anchors,
		bool	isFreeEndAttached,
		double	coefK,
		double	coefD,
		double	restLength
	)

The only constructor. Takes a list of anchors, a coefficient of stiffness, a coefficent of damping, and rest length of the spring.

Parameters

[in]	anchors	- a list of this spring cable's attachements
[in]	isFreeEndAttached	- boolean flag. If no, the spring only provides compression force. If yes, the spring is "attached" to both anchors, and provides a tension force too when the distance between anchors is greater than rest length.
[in]	coefK	- the stiffness of the spring. Must be positive
[in]	dampingCoefficient	- the damping in the spring. Must be non-negative.
[in]	restLength	- the length of the compression spring when unloaded.

The main constructor for this class

Definition at line 40 of file tgBulletCompressionSpring.cpp.

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tgBulletCompressionSpring::~tgBulletCompressionSpring ( )

virtual

The virtual destructor. Deletes all of the anchors including anchor1 and anchor2

Definition at line 87 of file tgBulletCompressionSpring.cpp.

Member Function Documentation

void tgBulletCompressionSpring::calculateAndApplyForce ( double dt )

protectedvirtual

Calculates the current forces that need to be applied to the rigid bodies, and applies them to the bodies of anchor1 and anchor2

This is the method that does the heavy lifting in this class. Called by step, it calculates what force the spring is experiencing, and applies that force to the rigid bodies it connects to.

Reimplemented in tgBulletUnidirComprSpr.

Definition at line 247 of file tgBulletCompressionSpring.cpp.

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const btVector3 tgBulletCompressionSpring::getAnchorDirectionUnitVector ( ) const

virtual

Return the unit vector in the direction of this spring

Returns the unit vector in the direction of this spring.

Definition at line 181 of file tgBulletCompressionSpring.cpp.

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const std::vector< const tgSpringCableAnchor * > tgBulletCompressionSpring::getAnchors ( ) const

virtual

Returns a const vector of const anchors. Currently casts from tgBulletSpringCableAnchors, which makes it impossible to return a reference

Todo:: figure out how to cast and pass by reference

Definition at line 296 of file tgBulletCompressionSpring.cpp.

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virtual const double tgBulletCompressionSpring::getCoefD ( ) const

inlinevirtual

Get the coefficent of damping

Definition at line 124 of file tgBulletCompressionSpring.h.

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virtual const double tgBulletCompressionSpring::getCoefK ( ) const

inlinevirtual

Get the coefficent of stiffness

Definition at line 116 of file tgBulletCompressionSpring.h.

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const double tgBulletCompressionSpring::getCurrentAnchorDistance ( ) const

virtual

Finds the distance between anchor1 and anchor2, and returns the length between them

Returns the distance between the two anchors. This is similar to the getActualLength function in tgBulletSpringCable.

Definition at line 139 of file tgBulletCompressionSpring.cpp.

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const double tgBulletCompressionSpring::getCurrentSpringLength ( ) const

virtual

Returns either restLength or current anchor distance, depending on isFreeEndAttached.

Returns the current length of the spring. If isFreeEndAttached, this can be either greater or less than m_restLength. If not, then spring can only exist in compression (less than m_restLength).

Reimplemented in tgBulletUnidirComprSpr.

Definition at line 151 of file tgBulletCompressionSpring.cpp.

virtual const double tgBulletCompressionSpring::getDampingForce ( ) const

inlinevirtual

Get the last value of the damping force

Definition at line 140 of file tgBulletCompressionSpring.h.

virtual const double tgBulletCompressionSpring::getRestLength ( ) const

inlinevirtual

Get the rest length of the spring (we're using these accessor functions per C++ style guidelines.)

Definition at line 149 of file tgBulletCompressionSpring.h.

const btVector3 tgBulletCompressionSpring::getSpringEndpoint ( ) const

virtual

Return the location of the free end of the spring. This is used, in particular, for rendering. See tgBulletRenderer.

Returns the location of the endpoint of the spring in space. The renderer uses this to draw lines more easily.

Reimplemented in tgBulletUnidirComprSpr.

Definition at line 201 of file tgBulletCompressionSpring.cpp.

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const double tgBulletCompressionSpring::getSpringForce ( ) const

virtual

Returns the force currently in the spring, either compression only / a positive force only (if isFreeEndAttached is false), or potentially either + or - force (if isFreeEndAttached == true).

Returns the current force in the spring. If ~isFreeEndAttached, this is zero if the distance between anchors is larger than restLength. Note that this does NOT include the force due to the damper, since that force is only temporary and isn't reallyt "the force in the spring" per se.

Reimplemented in tgBulletUnidirComprSpr.

Definition at line 217 of file tgBulletCompressionSpring.cpp.

virtual const double tgBulletCompressionSpring::getVelocity ( ) const

inlinevirtual

Get the last change in length / time

Definition at line 132 of file tgBulletCompressionSpring.h.

virtual const bool tgBulletCompressionSpring::isFreeEndAttached ( ) const

inlinevirtual

Return the boolean: is the free end attached?

Definition at line 157 of file tgBulletCompressionSpring.h.

void tgBulletCompressionSpring::step ( double dt )

virtual

Updates this object. Calls calculateAndApplyForce(dt)

Parameters

[in] dt,must be positive

Reimplemented in tgBulletUnidirComprSpr.

Definition at line 116 of file tgBulletCompressionSpring.cpp.

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Member Data Documentation

tgBulletSpringCableAnchor* const tgBulletCompressionSpring::anchor1

protected

The first attachement point for this spring cable. Storing it seperately makes a number of functions easier

Definition at line 186 of file tgBulletCompressionSpring.h.

tgBulletSpringCableAnchor* const tgBulletCompressionSpring::anchor2

protected

The other permanent attachment for this spring cable.

Definition at line 191 of file tgBulletCompressionSpring.h.

std::vector<tgBulletSpringCableAnchor*> tgBulletCompressionSpring::m_anchors

protected

The list of contact points. tgBulletSpringCable typically has two whereas tgBulletContactSpringCable will have more. Needs to be stored here for consistent rendering. Vector has the convienence of tgCast functions, and we used to need a random iterator to sort

Definition at line 180 of file tgBulletCompressionSpring.h.

const double tgBulletCompressionSpring::m_coefD

protected

The damping coefficient. Units of mass / sec. Must be non-negative

Definition at line 222 of file tgBulletCompressionSpring.h.

const double tgBulletCompressionSpring::m_coefK

protected

The stiffness coefficient Units of mass / sec ^2 Must be positive

Definition at line 215 of file tgBulletCompressionSpring.h.

double tgBulletCompressionSpring::m_dampingForce

protected

The force in the spring due to damping, at the last update step. Stored so we can get it without passing a dt