godot/thirdparty/bullet/BulletDynamics/ConstraintSolver/btSolve2LinearConstraint.cpp

/*
Bullet Continuous Collision Detection and Physics Library
Copyright (c) 2003-2006 Erwin Coumans  https://bulletphysics.org

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 "btSolve2LinearConstraint.h"

#include "BulletDynamics/Dynamics/btRigidBody.h"
#include "LinearMath/btVector3.h"
#include "btJacobianEntry.h"

void btSolve2LinearConstraint::resolveUnilateralPairConstraint(
	btRigidBody* body1,
	btRigidBody* body2,

	const btMatrix3x3& world2A,
	const btMatrix3x3& world2B,

	const btVector3& invInertiaADiag,
	const btScalar invMassA,
	const btVector3& linvelA, const btVector3& angvelA,
	const btVector3& rel_posA1,
	const btVector3& invInertiaBDiag,
	const btScalar invMassB,
	const btVector3& linvelB, const btVector3& angvelB,
	const btVector3& rel_posA2,

	btScalar depthA, const btVector3& normalA,
	const btVector3& rel_posB1, const btVector3& rel_posB2,
	btScalar depthB, const btVector3& normalB,
	btScalar& imp0, btScalar& imp1)
{
	(void)linvelA;
	(void)linvelB;
	(void)angvelB;
	(void)angvelA;

	imp0 = btScalar(0.);
	imp1 = btScalar(0.);

	btScalar len = btFabs(normalA.length()) - btScalar(1.);
	if (btFabs(len) >= SIMD_EPSILON)
		return;

	btAssert(len < SIMD_EPSILON);

	//this jacobian entry could be re-used for all iterations
	btJacobianEntry jacA(world2A, world2B, rel_posA1, rel_posA2, normalA, invInertiaADiag, invMassA,
						 invInertiaBDiag, invMassB);
	btJacobianEntry jacB(world2A, world2B, rel_posB1, rel_posB2, normalB, invInertiaADiag, invMassA,
						 invInertiaBDiag, invMassB);

	//const btScalar vel0 = jacA.getRelativeVelocity(linvelA,angvelA,linvelB,angvelB);
	//const btScalar vel1 = jacB.getRelativeVelocity(linvelA,angvelA,linvelB,angvelB);

	const btScalar vel0 = normalA.dot(body1->getVelocityInLocalPoint(rel_posA1) - body2->getVelocityInLocalPoint(rel_posA1));
	const btScalar vel1 = normalB.dot(body1->getVelocityInLocalPoint(rel_posB1) - body2->getVelocityInLocalPoint(rel_posB1));

	//	btScalar penetrationImpulse = (depth*contactTau*timeCorrection)  * massTerm;//jacDiagABInv
	btScalar massTerm = btScalar(1.) / (invMassA + invMassB);

	// calculate rhs (or error) terms
	const btScalar dv0 = depthA * m_tau * massTerm - vel0 * m_damping;
	const btScalar dv1 = depthB * m_tau * massTerm - vel1 * m_damping;

	// dC/dv * dv = -C

	// jacobian * impulse = -error
	//

	//impulse = jacobianInverse * -error

	// inverting 2x2 symmetric system (offdiagonal are equal!)
	//

	btScalar nonDiag = jacA.getNonDiagonal(jacB, invMassA, invMassB);
	btScalar invDet = btScalar(1.0) / (jacA.getDiagonal() * jacB.getDiagonal() - nonDiag * nonDiag);

	//imp0 = dv0 * jacA.getDiagonal() * invDet + dv1 * -nonDiag * invDet;
	//imp1 = dv1 * jacB.getDiagonal() * invDet + dv0 * - nonDiag * invDet;

	imp0 = dv0 * jacA.getDiagonal() * invDet + dv1 * -nonDiag * invDet;
	imp1 = dv1 * jacB.getDiagonal() * invDet + dv0 * -nonDiag * invDet;

	//[a b]								  [d -c]
	//[c d] inverse = (1 / determinant) * [-b a] where determinant is (ad - bc)

	//[jA nD] * [imp0] = [dv0]
	//[nD jB]   [imp1]   [dv1]
}

void btSolve2LinearConstraint::resolveBilateralPairConstraint(
	btRigidBody* body1,
	btRigidBody* body2,
	const btMatrix3x3& world2A,
	const btMatrix3x3& world2B,

	const btVector3& invInertiaADiag,
	const btScalar invMassA,
	const btVector3& linvelA, const btVector3& angvelA,
	const btVector3& rel_posA1,
	const btVector3& invInertiaBDiag,
	const btScalar invMassB,
	const btVector3& linvelB, const btVector3& angvelB,
	const btVector3& rel_posA2,

	btScalar depthA, const btVector3& normalA,
	const btVector3& rel_posB1, const btVector3& rel_posB2,
	btScalar depthB, const btVector3& normalB,
	btScalar& imp0, btScalar& imp1)
{
	(void)linvelA;
	(void)linvelB;
	(void)angvelA;
	(void)angvelB;

	imp0 = btScalar(0.);
	imp1 = btScalar(0.);

	btScalar len = btFabs(normalA.length()) - btScalar(1.);
	if (btFabs(len) >= SIMD_EPSILON)
		return;

	btAssert(len < SIMD_EPSILON);

	//this jacobian entry could be re-used for all iterations
	btJacobianEntry jacA(world2A, world2B, rel_posA1, rel_posA2, normalA, invInertiaADiag, invMassA,
						 invInertiaBDiag, invMassB);
	btJacobianEntry jacB(world2A, world2B, rel_posB1, rel_posB2, normalB, invInertiaADiag, invMassA,
						 invInertiaBDiag, invMassB);

	//const btScalar vel0 = jacA.getRelativeVelocity(linvelA,angvelA,linvelB,angvelB);
	//const btScalar vel1 = jacB.getRelativeVelocity(linvelA,angvelA,linvelB,angvelB);

	const btScalar vel0 = normalA.dot(body1->getVelocityInLocalPoint(rel_posA1) - body2->getVelocityInLocalPoint(rel_posA1));
	const btScalar vel1 = normalB.dot(body1->getVelocityInLocalPoint(rel_posB1) - body2->getVelocityInLocalPoint(rel_posB1));

	// calculate rhs (or error) terms
	const btScalar dv0 = depthA * m_tau - vel0 * m_damping;
	const btScalar dv1 = depthB * m_tau - vel1 * m_damping;

	// dC/dv * dv = -C

	// jacobian * impulse = -error
	//

	//impulse = jacobianInverse * -error

	// inverting 2x2 symmetric system (offdiagonal are equal!)
	//

	btScalar nonDiag = jacA.getNonDiagonal(jacB, invMassA, invMassB);
	btScalar invDet = btScalar(1.0) / (jacA.getDiagonal() * jacB.getDiagonal() - nonDiag * nonDiag);

	//imp0 = dv0 * jacA.getDiagonal() * invDet + dv1 * -nonDiag * invDet;
	//imp1 = dv1 * jacB.getDiagonal() * invDet + dv0 * - nonDiag * invDet;

	imp0 = dv0 * jacA.getDiagonal() * invDet + dv1 * -nonDiag * invDet;
	imp1 = dv1 * jacB.getDiagonal() * invDet + dv0 * -nonDiag * invDet;

	//[a b]								  [d -c]
	//[c d] inverse = (1 / determinant) * [-b a] where determinant is (ad - bc)

	//[jA nD] * [imp0] = [dv0]
	//[nD jB]   [imp1]   [dv1]

	if (imp0 > btScalar(0.0))
	{
		if (imp1 > btScalar(0.0))
		{
			//both positive
		}
		else
		{
			imp1 = btScalar(0.);

			// now imp0>0 imp1<0
			imp0 = dv0 / jacA.getDiagonal();
			if (imp0 > btScalar(0.0))
			{
			}
			else
			{
				imp0 = btScalar(0.);
			}
		}
	}
	else
	{
		imp0 = btScalar(0.);

		imp1 = dv1 / jacB.getDiagonal();
		if (imp1 <= btScalar(0.0))
		{
			imp1 = btScalar(0.);
			// now imp0>0 imp1<0
			imp0 = dv0 / jacA.getDiagonal();
			if (imp0 > btScalar(0.0))
			{
			}
			else
			{
				imp0 = btScalar(0.);
			}
		}
		else
		{
		}
	}
}

/*
void btSolve2LinearConstraint::resolveAngularConstraint(	const btMatrix3x3& invInertiaAWS,
											const btScalar invMassA,
											const btVector3& linvelA,const btVector3& angvelA,
											const btVector3& rel_posA1,
											const btMatrix3x3& invInertiaBWS,
											const btScalar invMassB,
											const btVector3& linvelB,const btVector3& angvelB,
											const btVector3& rel_posA2,

											btScalar depthA, const btVector3& normalA, 
											const btVector3& rel_posB1,const btVector3& rel_posB2,
											btScalar depthB, const btVector3& normalB, 
											btScalar& imp0,btScalar& imp1)
{

}
*/