godot/servers/physics/joints/cone_twist_joint_sw.cpp

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

/*
Bullet Continuous Collision Detection and Physics Library
ConeTwistJointSW 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
*/

#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_angularOnly = false;
	m_solveTwistLimit = false;
	m_solveSwingLimit = false;

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

	m_appliedImpulse = 0;
}

bool ConeTwistJointSW::setup(real_t p_timestep) {
	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_principal_inertia_axes().transposed(),
												B->get_principal_inertia_axes().transposed(),
												pivotAInW - A->get_transform().origin - A->get_center_of_mass(),
												pivotBInW - B->get_transform().origin - B->get_center_of_mass(),
												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 p_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 / p_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.) / p_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.) / p_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, real_t 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;
		case PhysicsServer::CONE_TWIST_MAX: break; // Can't happen, but silences warning
	}
}

real_t 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;
		case PhysicsServer::CONE_TWIST_MAX: break; // Can't happen, but silences warning
	}

	return 0;
}