godot/servers/physics/joints/pin_joint_sw.cpp

/*************************************************************************/
/*  pin_joint_sw.cpp                                                     */
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/* Copyright (c) 2007-2017 Juan Linietsky, Ariel Manzur.                 */
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/*
Adapted to Godot from the Bullet library.
See corresponding header file for licensing info.
*/

#include "pin_joint_sw.h"

bool PinJointSW::setup(real_t p_step) {

	m_appliedImpulse = real_t(0.);

	Vector3	normal(0,0,0);

	for (int i=0;i<3;i++)
	{
		normal[i] = 1;
		memnew_placement(&m_jac[i],JacobianEntrySW(
			A->get_principal_inertia_axes().transposed(),
			B->get_principal_inertia_axes().transposed(),
			A->get_transform().xform(m_pivotInA) - A->get_transform().origin - A->get_center_of_mass(),
			B->get_transform().xform(m_pivotInB) - B->get_transform().origin - B->get_center_of_mass(),
			normal,
			A->get_inv_inertia(),
			A->get_inv_mass(),
			B->get_inv_inertia(),
			B->get_inv_mass()));
		normal[i] = 0;
	}

	return true;
}

void PinJointSW::solve(real_t p_step){

	Vector3 pivotAInW = A->get_transform().xform(m_pivotInA);
	Vector3 pivotBInW = B->get_transform().xform(m_pivotInB);


	Vector3 normal(0,0,0);


	//Vector3 angvelA = A->get_transform().origin.getBasis().transpose() * A->getAngularVelocity();
	//Vector3 angvelB = B->get_transform().origin.getBasis().transpose() * B->getAngularVelocity();

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

		Vector3 rel_pos1 = pivotAInW - A->get_transform().origin;
		Vector3 rel_pos2 = pivotBInW - B->get_transform().origin;
		//this jacobian entry could be re-used for all iterations

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

		real_t rel_vel;
		rel_vel = normal.dot(vel);

	/*
		//velocity error (first order error)
		real_t rel_vel = m_jac[i].getRelativeVelocity(A->getLinearVelocity(),angvelA,
														B->getLinearVelocity(),angvelB);
	*/

		//positional error (zeroth order error)
		real_t depth = -(pivotAInW - pivotBInW).dot(normal); //this is the error projected on the normal

		real_t impulse = depth*m_tau/p_step  * jacDiagABInv -  m_damping * rel_vel * jacDiagABInv;

		real_t impulseClamp = m_impulseClamp;
		if (impulseClamp > 0)
		{
			if (impulse < -impulseClamp)
				impulse = -impulseClamp;
			if (impulse > impulseClamp)
				impulse = impulseClamp;
		}

		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);

		normal[i] = 0;
	}
}

void PinJointSW::set_param(PhysicsServer::PinJointParam p_param,real_t p_value) {

	switch(p_param)	 {
		case PhysicsServer::PIN_JOINT_BIAS: m_tau=p_value; break;
		case PhysicsServer::PIN_JOINT_DAMPING: m_damping=p_value; break;
		case PhysicsServer::PIN_JOINT_IMPULSE_CLAMP: m_impulseClamp=p_value; break;
	}
}

real_t PinJointSW::get_param(PhysicsServer::PinJointParam p_param) const{

	switch(p_param)	 {
		case PhysicsServer::PIN_JOINT_BIAS: return m_tau;
		case PhysicsServer::PIN_JOINT_DAMPING: return m_damping;
		case PhysicsServer::PIN_JOINT_IMPULSE_CLAMP: return m_impulseClamp;
	}

	return 0;
}

PinJointSW::PinJointSW(BodySW* p_body_a,const Vector3& p_pos_a,BodySW* p_body_b,const Vector3& p_pos_b) : JointSW(_arr,2) {

	A=p_body_a;
	B=p_body_b;
	m_pivotInA=p_pos_a;
	m_pivotInB=p_pos_b;

	m_tau=0.3;
	m_damping=1;
	m_impulseClamp=0;
	m_appliedImpulse=0;

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


}

PinJointSW::~PinJointSW() {



}