code clean up + check in examples

src/BulletSoftBody/btPreconditioner.h

@@ -0,0 +1,67 @@
+//
+//  btPreconditioner.h
+//  BulletSoftBody
+//
+//  Created by Xuchen Han on 7/18/19.
+//
+
+#ifndef BT_PRECONDITIONER_H
+#define BT_PRECONDITIONER_H
+
+class Preconditioner
+{
+public:
+    using TVStack = btAlignedObjectArray<btVector3>;
+    virtual void operator()(const TVStack& x, TVStack& b) = 0;
+    virtual void reinitialize(bool nodeUpdated) = 0;
+};
+
+class DefaultPreconditioner : public Preconditioner
+{
+public:
+    virtual void operator()(const TVStack& x, TVStack& b)
+    {
+        btAssert(b.size() == x.size());
+        for (int i = 0; i < b.size(); ++i)
+            b[i] = x[i];
+    }
+    virtual void reinitialize(bool nodeUpdated)
+    {
+        
+    }
+};
+
+class MassPreconditioner : public Preconditioner
+{
+    btAlignedObjectArray<btScalar> m_inv_mass;
+    const btAlignedObjectArray<btSoftBody *>& m_softBodies;
+public:
+    MassPreconditioner(const btAlignedObjectArray<btSoftBody *>& softBodies)
+    : m_softBodies(softBodies)
+    {
+    }
+    
+    virtual void reinitialize(bool nodeUpdated)
+    {
+        if (nodeUpdated)
+        {
+            m_inv_mass.clear();
+            for (int i = 0; i < m_softBodies.size(); ++i)
+            {
+                btSoftBody* psb = m_softBodies[i];
+                for (int j = 0; j < psb->m_nodes.size(); ++j)
+                    m_inv_mass.push_back(psb->m_nodes[j].m_im);
+            }
+        }
+    }
+    
+    virtual void operator()(const TVStack& x, TVStack& b)
+    {
+        btAssert(b.size() == x.size());
+        btAssert(m_inv_mass.size() == x.size());
+        for (int i = 0; i < b.size(); ++i)
+            b[i] = x[i] * m_inv_mass[i];
+    }
+};
+
+#endif /* BT_PRECONDITIONER_H */