godot/servers/physics/joints/pin_joint_sw.cpp

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/*  pin_joint_sw.cpp                                                     */
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/*
Adapted to Godot from the Bullet library.
*/

/*
Bullet Continuous Collision Detection and Physics Library
Copyright (c) 2003-2006 Erwin Coumans  http://continuousphysics.com/Bullet/

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.
*/

#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() {
}