finish deformable sleeping and add option for drag

src/BulletSoftBody/btDeformableBackwardEulerObjective.cpp

@@ -101,6 +101,10 @@ void btDeformableBackwardEulerObjective::applyForce(TVStack& force, bool setZero
     for (int i = 0; i < m_softBodies.size(); ++i)
     {
         btSoftBody* psb = m_softBodies[i];
+        if (!psb->isActive())
+        {
+            continue;
+        }
         for (int j = 0; j < psb->m_nodes.size(); ++j)
         {
             btScalar one_over_mass = (psb->m_nodes[j].m_im == 0) ? 0 : psb->m_nodes[j].m_im;

src/BulletSoftBody/btDeformableBodySolver.cpp

@@ -376,6 +376,7 @@ void btDeformableBodySolver::predictDeformableMotion(btSoftBody* psb, btScalar d
     for (i = 0, ni = psb->m_nodes.size(); i < ni; ++i)
     {
         btSoftBody::Node& n = psb->m_nodes[i];
+        n.m_v *= (1 - psb->m_cfg.drag);
         n.m_q = n.m_x + n.m_v * dt;
     }
     /* Bounds                */

src/BulletSoftBody/btDeformableGravityForce.h

@@ -80,6 +80,10 @@ public:
         for (int i = 0; i<m_softBodies.size();++i)
         {
             btSoftBody* psb = m_softBodies[i];
+            if (!psb->isActive())
+            {
+                continue;
+            }
             for (int j = 0; j < psb->m_nodes.size(); ++j)
             {
                 const btSoftBody::Node& node = psb->m_nodes[j];

src/BulletSoftBody/btDeformableMassSpringForce.h

@@ -51,6 +51,10 @@ public:
         for (int i = 0; i < m_softBodies.size(); ++i)
         {
             const btSoftBody* psb = m_softBodies[i];
+            if (!psb->isActive())
+            {
+                continue;
+            }
             for (int j = 0; j < psb->m_links.size(); ++j)
             {
                 const btSoftBody::Link& link = psb->m_links[j];
@@ -83,6 +87,10 @@ public:
         for (int i = 0; i < m_softBodies.size(); ++i)
         {
             const btSoftBody* psb = m_softBodies[i];
+            if (!psb->isActive())
+            {
+                continue;
+            }
             for (int j = 0; j < psb->m_links.size(); ++j)
             {
                 const btSoftBody::Link& link = psb->m_links[j];
@@ -108,6 +116,10 @@ public:
         for (int i = 0; i < m_softBodies.size(); ++i)
         {
             btSoftBody* psb = m_softBodies[i];
+            if (!psb->isActive())
+            {
+                continue;
+            }
             btScalar scaled_k_damp = m_dampingStiffness * scale;
             for (int j = 0; j < psb->m_links.size(); ++j)
             {
@@ -138,6 +150,10 @@ public:
         for (int i = 0; i < m_softBodies.size(); ++i)
         {
             const btSoftBody* psb = m_softBodies[i];
+            if (!psb->isActive())
+            {
+                continue;
+            }
             for (int j = 0; j < psb->m_links.size(); ++j)
             {
                 const btSoftBody::Link& link = psb->m_links[j];
@@ -160,6 +176,10 @@ public:
         for (int i = 0; i < m_softBodies.size(); ++i)
         {
             btSoftBody* psb = m_softBodies[i];
+            if (!psb->isActive())
+            {
+                continue;
+            }
             for (int j = 0; j < psb->m_nodes.size(); ++j)
             {
                 sz = btMax(sz, psb->m_nodes[j].index);
@@ -188,6 +208,10 @@ public:
         for (int i = 0; i < m_softBodies.size(); ++i)
         {
             const btSoftBody* psb = m_softBodies[i];
+            if (!psb->isActive())
+            {
+                continue;
+            }
             btScalar scaled_k = m_elasticStiffness * scale;
             for (int j = 0; j < psb->m_links.size(); ++j)
             {

src/BulletSoftBody/btDeformableNeoHookeanForce.h

@@ -93,6 +93,10 @@ public:
         for (int i = 0; i < m_softBodies.size(); ++i)
         {
             btSoftBody* psb = m_softBodies[i];
+            if (!psb->isActive())
+            {
+                continue;
+            }
             for (int j = 0; j < psb->m_tetraScratches.size(); ++j)
             {
                 btSoftBody::Tetra& tetra = psb->m_tetras[j];
@@ -111,6 +115,10 @@ public:
         for (int i = 0; i < m_softBodies.size(); ++i)
         {
             btSoftBody* psb = m_softBodies[i];
+            if (!psb->isActive())
+            {
+                continue;
+            }
             for (int j = 0; j < psb->m_nodes.size(); ++j)
             {
                 sz = btMax(sz, psb->m_nodes[j].index);

src/BulletSoftBody/btSoftBody.cpp

@@ -89,6 +89,7 @@ void btSoftBody::initDefaults()
 	m_cfg.piterations = 1;
 	m_cfg.diterations = 0;
 	m_cfg.citerations = 4;
+    m_cfg.drag = 0.01;
 	m_cfg.collisions = fCollision::Default;
     m_cfg.collisions |= fCollision::VF_DD;
 	m_pose.m_bvolume = false;

src/BulletSoftBody/btSoftBody.h

@@ -702,6 +702,7 @@ public:
 		tVSolverArray m_vsequence;  // Velocity solvers sequence
 		tPSolverArray m_psequence;  // Position solvers sequence
 		tPSolverArray m_dsequence;  // Drift solvers sequence
+        btScalar drag;           // deformable air drag
 	};
 	/* SolverState	*/
 	struct SolverState