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Petal simulation

Posted: Fri Apr 12, 2019 12:50 pm
by m_iDev_792
Hi, I'm new to Bullet physics. I'm working on plant modeling and I want to use Bullet physics to simulate petal material and handle the collisions between petals of different flowers. In my program petals are represented by triangle faces and they have no volume just like cloth and paper, but I want them to be harder than cloth and be able to keep their overall shape in a small collision.
Here are what I have done to do this(simulate petals with btSoftBody), the problem is that petals turn out to be too soft. I want them to be harder.
But I really have no idea which attribute of btSoftBody and btSoftBody::Material I should adjust to do this.

Code: Select all

  pSoftBody=btSoftBodyHelpers::CreateFromTriMesh(*worldInfo,pVertices,pTriangles,triangleNum);
  btSoftBody::Material *pMat=pSoftBody->appendMaterial();
  pMat->m_kLST = 0.5;
  pMat->m_kAST=1.0;
  pMat->m_kVST=1.0;
  pSoftBody->generateBendingConstraints(2,pMat);
  pSoftBody->m_cfg.kDF=0.5;
  pSoftBody->m_cfg.piterations=2;
  pSoftBody->m_cfg.kDP = 0.005;
  pSoftBody->m_cfg.kCHR = 0.1;
  pSoftBody->setTotalMass(10);
 
  pSoftBody->setMass(rootIndex,0);//set static nodes
  pSoftBody->setMass(farIndex,0);
I copied these parameters from Bullet SoftBody Demo, how to adjust them to make soft body harder(stronger shape preserve ability)?
thanks!

Re: Petal simulation

Posted: Fri Apr 12, 2019 1:56 pm
by steven
Could you try these two interfaces? i still think it is hard to implement your feature. the point is what will be used to overcome the gravity.
psb->setPose(false, true)
psb->generateClusters(8)

Re: Petal simulation

Posted: Fri Apr 12, 2019 2:14 pm
by steven
maybe the psb->setWindVelocity() can be used to overcome the gravity.

Re: Petal simulation

Posted: Sat Apr 13, 2019 4:40 am
by m_iDev_792
steven wrote:
Fri Apr 12, 2019 1:56 pm
Could you try these two interfaces? i still think it is hard to implement your feature. the point is what will be used to overcome the gravity.
psb->setPose(false, true)
psb->generateClusters(8)
Hi steven, thanks for your reply. I set the mass of top node and bottom node of petal to zero to overcome gravity and it works. I also tried setWindVelocity() which also works fine.
But now I have another problem that btSoftBody can't collide with btSoftBody. When two btSoftBody contact, they just penetrate each other while a btRigidBody does collide with a btSoftBody and bounces off.
I set the collisions flag of btSoftBody as

Code: Select all

pSoftBody->m_cfg.collisions = btSoftBody::fCollision::CL_SS | btSoftBody::fCollision::CL_RS;
but not working

Re: Petal simulation

Posted: Sat Apr 13, 2019 8:56 am
by steven
hi, can you try this interface btSoftBody::generateClusters(int k,int maxiterations) and ajust the parameter k to see if can get the expected result.

Re: Petal simulation

Posted: Sat Apr 13, 2019 10:03 am
by m_iDev_792
steven wrote:
Sat Apr 13, 2019 8:56 am
hi, can you try this interface btSoftBody::generateClusters(int k,int maxiterations) and ajust the parameter k to see if can get the expected result.
that's exactly what I forgot. I called pSoftBody->generateClusters(16) and pSoftBody->setMargin(0.01) and it worked great.
But larger margin value like 0.5 leads to a strange result.
thank you steven , have a good day! :mrgreen: