virtualx-engine/servers/physics/joints/cone_twist_joint_sw.cpp

#include "cone_twist_joint_sw.h"

static void plane_space(const Vector3& n, Vector3& p, Vector3& q) {

  if (Math::abs(n.z) > 0.707106781186547524400844362) {
    // choose p in y-z plane
    real_t a = n[1]*n[1] + n[2]*n[2];
    real_t k = 1.0/Math::sqrt(a);
    p=Vector3(0,-n[2]*k,n[1]*k);
    // set q = n x p
    q=Vector3(a*k,-n[0]*p[2],n[0]*p[1]);
  }
  else {
    // choose p in x-y plane
    real_t a = n.x*n.x + n.y*n.y;
    real_t k = 1.0/Math::sqrt(a);
    p=Vector3(-n.y*k,n.x*k,0);
    // set q = n x p
    q=Vector3(-n.z*p.y,n.z*p.x,a*k);
  }
}


static _FORCE_INLINE_ real_t atan2fast(real_t y, real_t x)
{
	real_t coeff_1 = Math_PI / 4.0f;
	real_t coeff_2 = 3.0f * coeff_1;
	real_t abs_y = Math::abs(y);
	real_t angle;
	if (x >= 0.0f) {
		real_t r = (x - abs_y) / (x + abs_y);
		angle = coeff_1 - coeff_1 * r;
	} else {
		real_t r = (x + abs_y) / (abs_y - x);
		angle = coeff_2 - coeff_1 * r;
	}
	return (y < 0.0f) ? -angle : angle;
}

ConeTwistJointSW::ConeTwistJointSW(BodySW* rbA,BodySW* rbB,const Transform& rbAFrame, const Transform& rbBFrame) :  JointSW(_arr,2) {

	A=rbA;
	B=rbB;


	m_rbAFrame=rbAFrame;
	m_rbBFrame=rbBFrame;

	m_swingSpan1 = Math_PI/4.0;
	m_swingSpan2 = Math_PI/4.0;
	m_twistSpan  = Math_PI*2;
	m_biasFactor = 0.3f;
	m_relaxationFactor = 1.0f;

	m_solveTwistLimit = false;
	m_solveSwingLimit = false;

	A->add_constraint(this,0);
	B->add_constraint(this,1);

	m_appliedImpulse=0;
}


bool	ConeTwistJointSW::setup(float p_step) {
	m_appliedImpulse = real_t(0.);

	//set bias, sign, clear accumulator
	m_swingCorrection = real_t(0.);
	m_twistLimitSign = real_t(0.);
	m_solveTwistLimit = false;
	m_solveSwingLimit = false;
	m_accTwistLimitImpulse = real_t(0.);
	m_accSwingLimitImpulse = real_t(0.);

	if (!m_angularOnly)
	{
		Vector3 pivotAInW = A->get_transform().xform(m_rbAFrame.origin);
		Vector3 pivotBInW = B->get_transform().xform(m_rbBFrame.origin);
		Vector3 relPos = pivotBInW - pivotAInW;

		Vector3 normal[3];
		if (relPos.length_squared() > CMP_EPSILON)
		{
			normal[0] = relPos.normalized();
		}
		else
		{
			normal[0]=Vector3(real_t(1.0),0,0);
		}

		plane_space(normal[0], normal[1], normal[2]);

		for (int i=0;i<3;i++)
		{
			memnew_placement(&m_jac[i], JacobianEntrySW(
				A->get_transform().basis.transposed(),
				B->get_transform().basis.transposed(),
				pivotAInW - A->get_transform().origin,
				pivotBInW - B->get_transform().origin,
				normal[i],
				A->get_inv_inertia(),
				A->get_inv_mass(),
				B->get_inv_inertia(),
				B->get_inv_mass()));
		}
	}

	Vector3 b1Axis1,b1Axis2,b1Axis3;
	Vector3 b2Axis1,b2Axis2;

	b1Axis1 = A->get_transform().basis.xform( this->m_rbAFrame.basis.get_axis(0) );
	b2Axis1 = B->get_transform().basis.xform( this->m_rbBFrame.basis.get_axis(0) );

	real_t swing1=real_t(0.),swing2 = real_t(0.);

	real_t swx=real_t(0.),swy = real_t(0.);
	real_t thresh = real_t(10.);
	real_t fact;

	// Get Frame into world space
	if (m_swingSpan1 >= real_t(0.05f))
	{
		b1Axis2 = A->get_transform().basis.xform( this->m_rbAFrame.basis.get_axis(1) );
//		swing1  = btAtan2Fast( b2Axis1.dot(b1Axis2),b2Axis1.dot(b1Axis1) );
		swx = b2Axis1.dot(b1Axis1);
		swy = b2Axis1.dot(b1Axis2);
		swing1  = atan2fast(swy, swx);
		fact = (swy*swy + swx*swx) * thresh * thresh;
		fact = fact / (fact + real_t(1.0));
		swing1 *= fact;

	}

	if (m_swingSpan2 >= real_t(0.05f))
	{
		b1Axis3 = A->get_transform().basis.xform( this->m_rbAFrame.basis.get_axis(2) );
//		swing2 = btAtan2Fast( b2Axis1.dot(b1Axis3),b2Axis1.dot(b1Axis1) );
		swx = b2Axis1.dot(b1Axis1);
		swy = b2Axis1.dot(b1Axis3);
		swing2  = atan2fast(swy, swx);
		fact = (swy*swy + swx*swx) * thresh * thresh;
		fact = fact / (fact + real_t(1.0));
		swing2 *= fact;
	}

	real_t RMaxAngle1Sq = 1.0f / (m_swingSpan1*m_swingSpan1);
	real_t RMaxAngle2Sq = 1.0f / (m_swingSpan2*m_swingSpan2);
	real_t EllipseAngle = Math::abs(swing1*swing1)* RMaxAngle1Sq + Math::abs(swing2*swing2) * RMaxAngle2Sq;

	if (EllipseAngle > 1.0f)
	{
		m_swingCorrection = EllipseAngle-1.0f;
		m_solveSwingLimit = true;

		// Calculate necessary axis & factors
		m_swingAxis = b2Axis1.cross(b1Axis2* b2Axis1.dot(b1Axis2) + b1Axis3* b2Axis1.dot(b1Axis3));
		m_swingAxis.normalize();

		real_t swingAxisSign = (b2Axis1.dot(b1Axis1) >= 0.0f) ? 1.0f : -1.0f;
		m_swingAxis *= swingAxisSign;

		m_kSwing =  real_t(1.) / (A->compute_angular_impulse_denominator(m_swingAxis) +
			B->compute_angular_impulse_denominator(m_swingAxis));

	}

	// Twist limits
	if (m_twistSpan >= real_t(0.))
	{
		Vector3 b2Axis2 = B->get_transform().basis.xform( this->m_rbBFrame.basis.get_axis(1) );
		Quat rotationArc = Quat(b2Axis1,b1Axis1);
		Vector3 TwistRef = rotationArc.xform(b2Axis2);
		real_t twist = atan2fast( TwistRef.dot(b1Axis3), TwistRef.dot(b1Axis2) );

		real_t lockedFreeFactor = (m_twistSpan > real_t(0.05f)) ? m_limitSoftness : real_t(0.);
		if (twist <= -m_twistSpan*lockedFreeFactor)
		{
			m_twistCorrection = -(twist + m_twistSpan);
			m_solveTwistLimit = true;

			m_twistAxis = (b2Axis1 + b1Axis1) * 0.5f;
			m_twistAxis.normalize();
			m_twistAxis *= -1.0f;

			m_kTwist = real_t(1.) / (A->compute_angular_impulse_denominator(m_twistAxis) +
				B->compute_angular_impulse_denominator(m_twistAxis));

		}	else
			if (twist >  m_twistSpan*lockedFreeFactor)
			{
				m_twistCorrection = (twist - m_twistSpan);
				m_solveTwistLimit = true;

				m_twistAxis = (b2Axis1 + b1Axis1) * 0.5f;
				m_twistAxis.normalize();

				m_kTwist = real_t(1.) / (A->compute_angular_impulse_denominator(m_twistAxis) +
					B->compute_angular_impulse_denominator(m_twistAxis));

			}
	}

	return true;
}

void	ConeTwistJointSW::solve(real_t	timeStep)
{

	Vector3 pivotAInW = A->get_transform().xform(m_rbAFrame.origin);
	Vector3 pivotBInW = B->get_transform().xform(m_rbBFrame.origin);

	real_t tau = real_t(0.3);

	//linear part
	if (!m_angularOnly)
	{
		Vector3 rel_pos1 = pivotAInW - A->get_transform().origin;
		Vector3 rel_pos2 = pivotBInW - B->get_transform().origin;

		Vector3 vel1 = A->get_velocity_in_local_point(rel_pos1);
		Vector3 vel2 = B->get_velocity_in_local_point(rel_pos2);
		Vector3 vel = vel1 - vel2;

		for (int i=0;i<3;i++)
		{
			const Vector3& normal = m_jac[i].m_linearJointAxis;
			real_t jacDiagABInv = real_t(1.) / m_jac[i].getDiagonal();

			real_t rel_vel;
			rel_vel = normal.dot(vel);
			//positional error (zeroth order error)
			real_t depth = -(pivotAInW - pivotBInW).dot(normal); //this is the error projected on the normal
			real_t impulse = depth*tau/timeStep  * jacDiagABInv -  rel_vel * jacDiagABInv;
			m_appliedImpulse += impulse;
			Vector3 impulse_vector = normal * impulse;
			A->apply_impulse(pivotAInW - A->get_transform().origin, impulse_vector);
			B->apply_impulse(pivotBInW - B->get_transform().origin, -impulse_vector);
		}
	}

	{
		///solve angular part
		const Vector3& angVelA = A->get_angular_velocity();
		const Vector3& angVelB = B->get_angular_velocity();

		// solve swing limit
		if (m_solveSwingLimit)
		{
			real_t amplitude = ((angVelB - angVelA).dot( m_swingAxis )*m_relaxationFactor*m_relaxationFactor + m_swingCorrection*(real_t(1.)/timeStep)*m_biasFactor);
			real_t impulseMag = amplitude * m_kSwing;

			// Clamp the accumulated impulse
			real_t temp = m_accSwingLimitImpulse;
			m_accSwingLimitImpulse = MAX(m_accSwingLimitImpulse + impulseMag, real_t(0.0) );
			impulseMag = m_accSwingLimitImpulse - temp;

			Vector3 impulse = m_swingAxis * impulseMag;

			A->apply_torque_impulse(impulse);
			B->apply_torque_impulse(-impulse);

		}

		// solve twist limit
		if (m_solveTwistLimit)
		{
			real_t amplitude = ((angVelB - angVelA).dot( m_twistAxis )*m_relaxationFactor*m_relaxationFactor + m_twistCorrection*(real_t(1.)/timeStep)*m_biasFactor );
			real_t impulseMag = amplitude * m_kTwist;

			// Clamp the accumulated impulse
			real_t temp = m_accTwistLimitImpulse;
			m_accTwistLimitImpulse = MAX(m_accTwistLimitImpulse + impulseMag, real_t(0.0) );
			impulseMag = m_accTwistLimitImpulse - temp;

			Vector3 impulse = m_twistAxis * impulseMag;

			A->apply_torque_impulse(impulse);
			B->apply_torque_impulse(-impulse);

		}

	}

}

void ConeTwistJointSW::set_param(PhysicsServer::ConeTwistJointParam p_param, float p_value) {

	switch(p_param) {
		case PhysicsServer::CONE_TWIST_JOINT_SWING_SPAN: {

			m_swingSpan1=p_value;
			m_swingSpan2=p_value;
		} break;
		case PhysicsServer::CONE_TWIST_JOINT_TWIST_SPAN: {

			m_twistSpan=p_value;
		} break;
		case PhysicsServer::CONE_TWIST_JOINT_BIAS: {

			m_biasFactor=p_value;
		} break;
		case PhysicsServer::CONE_TWIST_JOINT_SOFTNESS: {

			m_limitSoftness=p_value;
		} break;
		case PhysicsServer::CONE_TWIST_JOINT_RELAXATION: {

			m_relaxationFactor=p_value;
		} break;
	}
}

float ConeTwistJointSW::get_param(PhysicsServer::ConeTwistJointParam p_param) const{

	switch(p_param) {
		case PhysicsServer::CONE_TWIST_JOINT_SWING_SPAN: {

			return m_swingSpan1;
		} break;
		case PhysicsServer::CONE_TWIST_JOINT_TWIST_SPAN: {

			return m_twistSpan;
		} break;
		case PhysicsServer::CONE_TWIST_JOINT_BIAS: {

			return m_biasFactor;
		} break;
		case PhysicsServer::CONE_TWIST_JOINT_SOFTNESS: {

			return m_limitSoftness;
		} break;
		case PhysicsServer::CONE_TWIST_JOINT_RELAXATION: {

			return m_relaxationFactor;
		} break;
	}

	return 0;
}