Sleeve over hinge/elbow joint demo

pmanandhar · Post by **pmanandhar** » Mon Mar 12, 2012 8:51 pm

Hi,

I have created a sleeved joint. If you want, I have reproduced source code to be integrated into the SoftDemo.cpp file. A video of screen-captures is posted at: http://youtu.be/LiYYqO2BxyQ

I also have a question, request for improvement. When the joint includes a "ball", body3 in the code below, at large joint angles, the cloth passes through the ball. I think it is similar to some cloth problems that other people were reporting in this forum. If you can fix it, please do so. I have been trying to fix it with smaller timesteps, collision margins, and other things suggested without much success. This also happens if the joint is flexed too fast.

Thanks, Prakash.

SoftDemo.cpp

Code: Select all

static btScalar SleeveTriMesh_GetX(const int m, const int M, const btVector3& origin, const btScalar r)
{
	return origin.x() + r*cos(2*M_PI/(M + 0.0)*m);
}

static btScalar SleeveTriMesh_GetZ(const int m, const int M, const btVector3& origin, const btScalar r)
{
	return origin.z() + r*sin(2*M_PI/(M + 0.0)*m);
}

static btScalar SleeveTriMesh_GetY(const int n, const int N, const btVector3& origin, const btScalar h)
{
	return origin.y() + h*n/(N - 1.0);
}

static void Init_SleevedJoint_GetSleeveTriMesh(btScalar*	vertices,
		int* triangles,
		const int M, const int N, const btVector3& origin, const btScalar radius, const btScalar height)
{
	for(int n = 0; n < N-1; n++)
	for(int m = 0; m < M; m++)
	{
		int p = n*M + m;
		vertices[p*3 + 0] = SleeveTriMesh_GetX(m, M, origin, radius);
		vertices[p*3 + 1] = SleeveTriMesh_GetY(n, N, origin, height);
		vertices[p*3 + 2] = SleeveTriMesh_GetZ(m, M, origin, radius);
		triangles[6*p + 0] = p;
		triangles[6*p + 1] = p + M;
		triangles[6*p + 2] = (m == M - 1)?p - M + 1:p + 1;
		triangles[6*p + 3] = triangles[6*p + 2];
		triangles[6*p + 4] = p + M;
		triangles[6*p + 5] = triangles[6*p + 2] + M;
	}

	for(int m = 0; m < M; m++)
	{
		int n = N - 1;
		int p = n*M + m;
		vertices[p*3 + 0] = SleeveTriMesh_GetX(m, M, origin, radius);
		vertices[p*3 + 1] = SleeveTriMesh_GetY(n, N, origin, height);
		vertices[p*3 + 2] = SleeveTriMesh_GetZ(m, M, origin, radius);
	}
}

//
// Joint with sleeve.
//
static void	Init_SleevedJoint(SoftDemo* pdemo)
{
	const int COLLISION_MARGIN = 0.001;
	const btScalar Z_LOCATION = 2.0;
	const int M_PATCH = 30, N_PATCH = 30;
	btScalar vertices[M_PATCH*N_PATCH*3];
	const int ntriangles = M_PATCH*(N_PATCH - 1)*2;
	int triangles[ntriangles*3];

	Init_SleevedJoint_GetSleeveTriMesh(vertices, triangles,
		M_PATCH, N_PATCH, btVector3(0, 1.5, Z_LOCATION), 2.1, 19);

//#define SLEEVE_DEBUG 1

#ifdef SLEEVE_DEBUG
	for(int nv = 0; nv < M_PATCH*N_PATCH*3; nv++)
		printf("vertices(%d) = %g\n", nv, vertices[nv]);
#endif

	//
	
	btTransform startTransform;
	startTransform.setIdentity();
	startTransform.setOrigin(btVector3(0, 4, Z_LOCATION));
	btRigidBody* body1 = pdemo->localCreateRigidBody(50,startTransform,new btCapsuleShape(2,6));
	body1->getCollisionShape()->setMargin(COLLISION_MARGIN);
	body1->setRestitution(1.0);
	body1->setDamping(0.9, 0.9);
	body1->setCcdMotionThreshold(0.001);
	
	startTransform.setIdentity();
	startTransform.setOrigin(btVector3(0, 10.6, Z_LOCATION));
	btRigidBody* body3 = pdemo->localCreateRigidBody(00,startTransform,new btSphereShape(1.5));
	body3->getCollisionShape()->setMargin(COLLISION_MARGIN);
	body3->setRestitution(1.0);
	body3->setCcdMotionThreshold(0.001);

	startTransform.setIdentity();
	startTransform.setOrigin(btVector3(0, 17.2, Z_LOCATION));
	btRigidBody* body2 = pdemo->localCreateRigidBody(00,startTransform,new btCapsuleShape(2,6));
	body2->getCollisionShape()->setMargin(COLLISION_MARGIN);

	btHingeConstraint *hingeC = 
		new btHingeConstraint(*body1,  
		btVector3(0, 5.5, 0),
		btVector3(0, 0, 1)
		);
	hingeC->setLimit(btScalar(-M_PI_4), btScalar(M_PI_4));
	pdemo->getDynamicsWorld()->addConstraint(hingeC, false);

	btSoftBody*	psb = btSoftBodyHelpers::CreateFromTriMesh( pdemo->m_softBodyWorldInfo,
			vertices, triangles, ntriangles, false);
	psb->getCollisionShape()->setMargin(COLLISION_MARGIN);
	btSoftBody::Material* pm=psb->appendMaterial();
	pm->m_kLST		=	0.1;
	//pm->m_flags		-=	btSoftBody::fMaterial::DebugDraw;
	psb->generateBendingConstraints(3,pm);
	psb->setTotalMass(10);
	//psb->setFriction(500.0);
	psb->m_cfg.kDF = 0.5;
	psb->m_cfg.kDP = 0.2;
	psb->m_cfg.kKHR = 1.0;
	psb->m_cfg.kPR = 0.5;
	//psb->m_cfg.piterations = 1;
	psb->m_cfg.timescale = 0.1;
	psb->setContactProcessingThreshold(0);
	psb->m_cfg.collisions = btSoftBody::fCollision::SDF_RS +
		btSoftBody::fCollision::CL_SS +
		btSoftBody::fCollision::CL_SELF;
	//psb->generateClusters(64);
	psb->setPose(true, false);
	pdemo->getSoftDynamicsWorld()->addSoftBody(psb);


	for (int m = 0; m < M_PATCH; m++) {
		psb->appendAnchor(m, body1, false, 1.0);
		psb->appendAnchor(M_PATCH*N_PATCH - m - 1, body2, false, 1.0);
	}
	pdemo->getDynamicsWorld()->getSolverInfo().m_splitImpulse = true;
	
	pdemo->m_cutting=true;
}

SoftDemo.cpp, Init section

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	/* Init		*/ 
	void (*demofncs[])(SoftDemo*)=
	{
		Init_Cloth,
		Init_Pressure,
		Init_Volume,
		Init_Ropes,
		Init_RopeAttach,
		Init_ClothAttach,
		Init_Sticks,	
		Init_Collide,
		Init_Collide2,
		Init_Collide3,
		Init_Impact,
		Init_Aero,
		Init_Aero2,
		Init_Friction,			
		Init_Torus,
		Init_TorusMatch,
		Init_Bunny,
		Init_BunnyMatch,
		Init_Cutting1,
		Init_ClusterDeform,
		Init_ClusterCollide1,
		Init_ClusterCollide2,
		Init_ClusterSocket,
		Init_ClusterHinge,
		Init_ClusterCombine,
		Init_ClusterCar,
		Init_ClusterRobot,
		Init_ClusterStackSoft,
		Init_ClusterStackMixed,
		Init_TetraCube,
		Init_TetraBunny,
		Init_SleevedJoint
	};

SoftDemo.h

Code: Select all

MACRO_SOFT_DEMO(30)//Init_SleevedJointDemo

pmanandhar · Post by **pmanandhar** » Tue Mar 13, 2012 12:26 am

pmanandhar wrote: I also have a question, request for improvement. When the joint includes a "ball", body3 in the code below, at large joint angles, the cloth passes through the ball. I think it is similar to some cloth problems that other people were reporting in this forum. If you can fix it, please do so. I have been trying to fix it with smaller timesteps, collision margins, and other things suggested without much success. This also happens if the joint is flexed too fast.

As I am experimenting with it, having a higher mesh-density combined with smaller time-steps seems to help, especially the fabric is allowed to "bake"/settle to an equilibrium position.

Adjusted code, only modified portions:

Code: Select all

const int M_PATCH = 50, N_PATCH = 50;

Added possibility for the elbow, sphere to move around a little bit:

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startTransform.setIdentity();
	startTransform.setOrigin(btVector3(0, 10.6, Z_LOCATION));
	btRigidBody* body3 = pdemo->localCreateRigidBody(50,startTransform,new btSphereShape(1.5));
	body3->getCollisionShape()->setMargin(COLLISION_MARGIN);
	body3->setRestitution(1.0);
	body3->setCcdMotionThreshold(0.001);
	btHingeConstraint *hingeC3 = 
		new btHingeConstraint(*body3,  
		btVector3(0, 1.5, 0),
		btVector3(0, 0, 1)
		);
	hingeC3->setLimit(btScalar(-M_PI_4/2), btScalar(M_PI_4/2));
	pdemo->getDynamicsWorld()->addConstraint(hingeC3, false);

Increased step-time resolution, in void SoftDemo::clientMoveAndDisplay():

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numSimSteps = m_dynamicsWorld->stepSimulation(dt,10,1./420.f);

Real-Time Physics Simulation Forum

Sleeve over hinge/elbow joint demo

Sleeve over hinge/elbow joint demo

Re: Sleeve over hinge/elbow joint demo