Soft body parts disappear

[Eaglegor]

The problem can be seen in this video:
http://youtu.be/8HCf_Si3yMQ

When I touch the softbody with two different kinematic bodies (instruments) some parts of it seem to disappear. I have no exact idea of what is wrong.
Both instruments are using compound shapes. The tube-linke instrument contains the single box shape. The grasping instrument contains one capsule-shape for each part.
Floor is static and contains a compound shape with single box in it.

The parameters of soft body are:

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m_cfg.kDP = 0; // Damping coefficient [0,1]
m_cfg.kPR = 0; // Pressure coefficient [-inf,+inf]
m_cfg.kDF = 1; // Dynamic friction coefficient [0,1]
m_cfg.kCHR = 1; // Rigid contacts hardness [0,1]
m_cfg.kKHR = 1; // Kinetic contacts hardness [0,1]
m_cfg.kSHR = 1; // Soft contacts hardness [0,1]
m_cfg.kSRHR_CL =  1; // Soft vs rigid hardness [0,1] (cluster only)
m_cfg.kSKHR_CL = 1; // Soft vs kinetic hardness [0,1] (cluster only)
m_cfg.kSSHR_CL = 1; // Soft vs soft hardness [0,1] (cluster only)
m_cfg.viterations = 0; // Velocities solver iterations
m_cfg.piterations = 8; // Positions solver iterations
m_cfg.collisions = btSoftBody::fCollision::CL_RS | btSoftBody::fCollision::CL_SS; // Collision flags

When I use SDF_RS as a collision flag I don't see such effect.

[Erwin Coumans]

Some issues might be fixed in very latest SVN version, can you test with the trunk version at http://bullet.googlecode.com?

The softbody clusters have issues indeed. You could try to reproduce it in one of the demos?
For example, you could try this:
Make the bug reproducible in your own software (disable user input and other random factors, for example recording the user input and playback next time).
Then serialize the simulation to a .bullet file, right before things go wrong. See http://bulletphysics.org/mediawiki-1.5. ... ialization
Then load the serialized .bullet file in the Bullet SerializeDemo (with softbody enabled) and see if it happens there too.
Then file an issue in the issue tracker.

[Eaglegor]

Thanks for an answer! I'll try do it in the near future when I'll have some free time.

[Eaglegor]

I reproduced this issue in Bullet trunk version demos (revision 2644).

With the default model from soft demo it behaves as expected: http://youtu.be/Ki8YcJDk7vU
With my own cube model (it's different from default) I get an unxepected behavior: http://youtu.be/9VY_wiyX1ms

There is a modified Init_TetraCube from demo:

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static void	Init_TetraCube(SoftDemo* pdemo)
{
	/*btSoftBody* psb=btSoftBodyHelpers::CreateFromTetGenData(pdemo->m_softBodyWorldInfo,
															TetraCube::getElements(),
															0,
															TetraCube::getNodes(),
															false,true,true);*/
	
	btSoftBody* psb=btSoftBodyHelpers::CreateFromTetGenData(pdemo->m_softBodyWorldInfo,
															"cube.1.ele",
															"cube.1.node",
															false,true,true);

	pdemo->getSoftDynamicsWorld()->addSoftBody(psb);
	psb->scale(btVector3(0.3,0.3,0.3));
	//psb->scale(btVector3(4,4,4));
	psb->translate(btVector3(0,5,0));
	//psb->setVolumeMass(30000);

	for(size_t i=0; i<psb->m_nodes.size(); ++i){
		psb->m_nodes[i].m_im = 1/0.01;
	}


	///fix one vertex
	//psb->setMass(0,0);
	//psb->setMass(10,0);
	//psb->setMass(20,0);
	psb->m_cfg.piterations=4;
	//psb->generateClusters(128);
	psb->generateClusters(64);
	//psb->getCollisionShape()->setMargin(0.5);

	psb->getCollisionShape()->setMargin(0.01);
	psb->m_cfg.collisions	=	btSoftBody::fCollision::CL_SS+	btSoftBody::fCollision::CL_RS
		//+ btSoftBody::fCollision::CL_SELF
		;
	psb->m_materials[0]->m_kLST=1;
	pdemo->m_cutting=false;	

	/*psb=btSoftBodyHelpers::CreateFromTetGenData(pdemo->m_softBodyWorldInfo,
															TetraCube::getElements(),
															0,
															TetraCube::getNodes(),
															false,true,true);*/

	psb=btSoftBodyHelpers::CreateFromTetGenData(pdemo->m_softBodyWorldInfo,
															"cube.1.ele",
															"cube.1.node",
															false,true,true);
	pdemo->getSoftDynamicsWorld()->addSoftBody(psb);
	psb->scale(btVector3(0.3,0.3,0.3));
	//psb->scale(btVector3(4,4,4));
	psb->translate(btVector3(0,40,0));
	//psb->setVolumeMass(30000);
	
	for(size_t i=0; i<psb->m_nodes.size(); ++i){
		psb->m_nodes[i].m_im = 1/0.01;
	}

	
	///fix one vertex
	//psb->setMass(0,0);
	//psb->setMass(10,0);
	//psb->setMass(20,0);
	psb->m_cfg.piterations=4;
	//psb->generateClusters(128);
	psb->generateClusters(64);
	//psb->getCollisionShape()->setMargin(0.5);

	psb->getCollisionShape()->setMargin(0.01);
	psb->m_cfg.collisions	=	btSoftBody::fCollision::CL_SS+	btSoftBody::fCollision::CL_RS
		//+ btSoftBody::fCollision::CL_SELF
		;
	psb->m_materials[0]->m_kLST=1;
	pdemo->m_cutting=false;	

}

Tet and ele files ale attached.
Loading tet and ele files is performed by this function:

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/* Create from TetGen .ele, .face, .node data							*/ 
btSoftBody*	btSoftBodyHelpers::CreateFromTetGenData(btSoftBodyWorldInfo& worldInfo,
													const char* ele,
													const char* node,
													bool bfacelinks,
													bool btetralinks,
													bool bfacesfromtetras)
{
	std::ifstream in_node(node);
	std::ifstream in_ele(ele);

	std::string node_string;
	std::string ele_string;

	while(!in_node.eof()){
		char c;
		in_node.get(c);
		node_string+=c;
	}

	while(!in_ele.eof()){
		char c;
		in_ele.get(c);
		ele_string+=c;
	}

	return btSoftBodyHelpers::CreateFromTetGenData(worldInfo, ele_string.c_str(), 0, node_string.c_str(), bfacelinks, btetralinks, bfacesfromtetras);
}

I'll post this issue in tracker soon.

UPD: related issue: http://code.google.com/p/bullet/issues/detail?id=730