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Bullet Continuous Collision Detection and Physics Library
btConeTwistConstraint is Copyright (c) 2007 Starbreeze Studios

This software is provided 'as-is', without any express or implied warranty.
In no event will the authors be held liable for any damages arising from the use of this software.
Permission is granted to anyone to use this software for any purpose, 
including commercial applications, and to alter it and redistribute it freely, 
subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.

Written by: Marcus Hennix


btConeTwistConstraint can be used to simulate ragdoll joints (upper arm, leg etc).
It is a fixed translation, 3 degree-of-freedom (DOF) rotational "joint".
It divides the 3 rotational DOFs into swing (movement within a cone) and twist.
Swing is divided into swing1 and swing2 which can have different limits, giving an elliptical shape.
(Note: the cone's base isn't flat, so this ellipse is "embedded" on the surface of a sphere.)

In the contraint's frame of reference:
twist is along the x-axis,
and swing 1 and 2 are along the z and y axes respectively.


#include "LinearMath/btVector3.h"
#include "btJacobianEntry.h"
#include "btTypedConstraint.h"

class btRigidBody;

///btConeTwistConstraint can be used to simulate ragdoll joints (upper arm, leg etc)
00047 class btConeTwistConstraint : public btTypedConstraint
      btJacobianEntry   m_jac[3]; //3 orthogonal linear constraints

      btTransform m_rbAFrame; 
      btTransform m_rbBFrame;

      btScalar    m_limitSoftness;
      btScalar    m_biasFactor;
      btScalar    m_relaxationFactor;

      btScalar    m_damping;

      btScalar    m_swingSpan1;
      btScalar    m_swingSpan2;
      btScalar    m_twistSpan;

      btScalar    m_fixThresh;

      btVector3   m_swingAxis;
      btVector3   m_twistAxis;

      btScalar    m_kSwing;
      btScalar    m_kTwist;

      btScalar    m_twistLimitSign;
      btScalar    m_swingCorrection;
      btScalar    m_twistCorrection;

      btScalar    m_twistAngle;

      btScalar    m_accSwingLimitImpulse;
      btScalar    m_accTwistLimitImpulse;

      bool        m_angularOnly;
      bool        m_solveTwistLimit;
      bool        m_solveSwingLimit;

      bool  m_useSolveConstraintObsolete;

      // not yet used...
      btScalar    m_swingLimitRatio;
      btScalar    m_twistLimitRatio;
      btVector3   m_twistAxisA;

      // motor
      bool         m_bMotorEnabled;
      bool         m_bNormalizedMotorStrength;
      btQuaternion m_qTarget;
      btScalar     m_maxMotorImpulse;
      btVector3    m_accMotorImpulse;

      btConeTwistConstraint(btRigidBody& rbA,btRigidBody& rbB,const btTransform& rbAFrame, const btTransform& rbBFrame);
      btConeTwistConstraint(btRigidBody& rbA,const btTransform& rbAFrame);


      virtual void      buildJacobian();

      virtual void getInfo1 (btConstraintInfo1* info);
      virtual void getInfo2 (btConstraintInfo2* info);

      virtual     void  solveConstraintObsolete(btSolverBody& bodyA,btSolverBody& bodyB,btScalar      timeStep);

      void  updateRHS(btScalar      timeStep);

      const btRigidBody& getRigidBodyA() const
            return m_rbA;
      const btRigidBody& getRigidBodyB() const
            return m_rbB;

      void  setAngularOnly(bool angularOnly)
            m_angularOnly = angularOnly;

      void  setLimit(int limitIndex,btScalar limitValue)
            switch (limitIndex)
            case 3:
                        m_twistSpan = limitValue;
            case 4:
                        m_swingSpan2 = limitValue;
            case 5:
                        m_swingSpan1 = limitValue;

      // setLimit(), a few notes:
      // _softness:
      //          0->1, recommend ~0.8->1.
      //          describes % of limits where movement is free.
      //          beyond this softness %, the limit is gradually enforced until the "hard" (1.0) limit is reached.
      // _biasFactor:
      //          0->1?, recommend 0.3 +/-0.3 or so.
      //          strength with which constraint resists zeroth order (angular, not angular velocity) limit violation.
      // __relaxationFactor:
      //          0->1, recommend to stay near 1.
      //          the lower the value, the less the constraint will fight velocities which violate the angular limits.
      void  setLimit(btScalar _swingSpan1,btScalar _swingSpan2,btScalar _twistSpan, btScalar _softness = 1.f, btScalar _biasFactor = 0.3f, btScalar _relaxationFactor = 1.0f)
            m_swingSpan1 = _swingSpan1;
            m_swingSpan2 = _swingSpan2;
            m_twistSpan  = _twistSpan;

            m_limitSoftness =  _softness;
            m_biasFactor = _biasFactor;
            m_relaxationFactor = _relaxationFactor;

      const btTransform& getAFrame() { return m_rbAFrame; };      
      const btTransform& getBFrame() { return m_rbBFrame; };

      inline int getSolveTwistLimit()
            return m_solveTwistLimit;

      inline int getSolveSwingLimit()
            return m_solveTwistLimit;

      inline btScalar getTwistLimitSign()
            return m_twistLimitSign;

      void calcAngleInfo();
      void calcAngleInfo2();

      inline btScalar getSwingSpan1()
            return m_swingSpan1;
      inline btScalar getSwingSpan2()
            return m_swingSpan2;
      inline btScalar getTwistSpan()
            return m_twistSpan;
      inline btScalar getTwistAngle()
            return m_twistAngle;
      bool isPastSwingLimit() { return m_solveSwingLimit; }

      void setDamping(btScalar damping) { m_damping = damping; }

      void enableMotor(bool b) { m_bMotorEnabled = b; }
      void setMaxMotorImpulse(btScalar maxMotorImpulse) { m_maxMotorImpulse = maxMotorImpulse; m_bNormalizedMotorStrength = false; }
      void setMaxMotorImpulseNormalized(btScalar maxMotorImpulse) { m_maxMotorImpulse = maxMotorImpulse; m_bNormalizedMotorStrength = true; }

      btScalar getFixThresh() { return m_fixThresh; }
      void setFixThresh(btScalar fixThresh) { m_fixThresh = fixThresh; }

      // setMotorTarget:
      // q: the desired rotation of bodyA wrt bodyB.
      // note: if q violates the joint limits, the internal target is clamped to avoid conflicting impulses (very bad for stability)
      // note: don't forget to enableMotor()
      void setMotorTarget(const btQuaternion &q);

      // same as above, but q is the desired rotation of frameA wrt frameB in constraint space
      void setMotorTargetInConstraintSpace(const btQuaternion &q);

      btVector3 GetPointForAngle(btScalar fAngleInRadians, btScalar fLength) const;

      void init();

      void computeConeLimitInfo(const btQuaternion& qCone, // in
            btScalar& swingAngle, btVector3& vSwingAxis, btScalar& swingLimit); // all outs

      void computeTwistLimitInfo(const btQuaternion& qTwist, // in
            btScalar& twistAngle, btVector3& vTwistAxis); // all outs

      void adjustSwingAxisToUseEllipseNormal(btVector3& vSwingAxis) const;


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