Verlet :: particle/sphere/plane

public class VerletParticle
{
   public final Vec3 now, old;
   public float      invWeight;

   public VerletParticle()
   {
      this.old = new Vec3();
      this.now = new Vec3();
      this.invWeight = 1.0f;
   }
   
   public void setInfiniteWeight()
   {
      this.invWeight = 0.0f;
   }

   public void setWeight(float weight)
   {
      this.invWeight = 1.0f / weight;
   }

   //

   public final void setPosition(Vec3 vec)
   {
      this.setPosition(vec.x, vec.y, vec.z);
   }

   public final void setPosition(float x, float y, float z)
   {
      float xVel = now.x - old.x;
      float yVel = now.y - old.y;
      float zVel = now.z - old.z;

      now.x = x;
      now.y = y;
      now.z = z;

      old.x = x - xVel;
      old.y = y - yVel;
      old.z = z - zVel;
   }

   public final void getPosition(Vec3 vec)
   {
      vec.x = now.x;
      vec.y = now.y;
      vec.z = now.z;
   }

   //

   public void translate(Vec3 vec)
   {
      this.translate(vec.x, vec.y, vec.z);
   }

   public void translate(float x, float y, float z)
   {
      this.setPosition(now.x + x, now.y + y, now.z + z);
   }

   //

   public final void addForce(Vec3 vec)
   {
      this.addForce(vec.x, vec.y, vec.z);
   }

   public final void addForce(float x, float y, float z)
   {
      this.addVelocity(x * invWeight, y * invWeight, z * invWeight);
   }

   //

   public final void setVelocity(Vec3 vec)
   {
      this.setVelocity(vec.x, vec.y, vec.z);
   }

   public final void setVelocity(float x, float y, float z)
   {
      old.x = now.x - x;
      old.y = now.y - y;
      old.z = now.z - z;
   }

   public final void addVelocity(float x, float y, float z)
   {
      old.x = old.x - x;
      old.y = old.y - y;
      old.z = old.z - z;
   }

   public final void getVelocity(Vec3 vec)
   {
      vec.x = now.x - old.x;
      vec.y = now.y - old.y;
      vec.z = now.z - old.z;
   }

   public final void mulVelocity(float factor)
   {
      float xNow = now.x;
      float yNow = now.y;
      float zNow = now.z;

      old.x = xNow - (xNow - old.x) * factor;
      old.y = yNow - (yNow - old.y) * factor;
      old.z = zNow - (zNow - old.z) * factor;
   }

   //

   public final void tick()
   {
      float xOld = old.x;
      float yOld = old.y;
      float zOld = old.z;

      old.x = now.x;
      old.y = now.y;
      old.z = now.z;

      now.x += now.x - xOld;
      now.y += now.y - yOld;
      now.z += now.z - zOld;
   }
}

public class VerletPlane
{
   public float nx, ny, nz, d;

   public final void inferValues(Vec3 src, Vec3 dst)
   {
      float nx = dst.x - src.x;
      float ny = dst.y - src.y;
      float nz = dst.z - src.z;

      float d = (float) Math.sqrt(nx * nx + ny * ny + nz * nz);
      nx /= d;
      ny /= d;
      nz /= d;

      float d2 = VecMath.dot(src, src);
      d2 = (d2 == 0.0f) ? 1.0f : (float) Math.sqrt(d2);
      float nx2 = src.x / d2;
      float ny2 = src.y / d2;
      float nz2 = src.z / d2;

      d2 *= nx * nx2 + ny * ny2 + nz * nz2;

      this.nx = nx;
      this.ny = ny;
      this.nz = nz;
      this.d = d2;
   }

   public final static VerletPlane infer(Vec3 src, Vec3 dst)
   {
      VerletPlane plane = new VerletPlane();
      plane.inferValues(src, dst);
      return plane;
   }
}

public class VerletSphere
{
   public final VerletParticle particle;
   public float                radius;
   public float                invFriction = 0.1f;
   public float                drag        = 0.0f;

   public VerletSphere(float rad)
   {
      this(new VerletParticle(), rad);
   }

   public VerletSphere(VerletParticle p, float rad)
   {
      this.particle = p;
      this.radius = rad;
   }

   public void setFriction(float friction)
   {
      this.invFriction = 1.0f - friction;
   }

   public VerletParticle getParticle()
   {
      return particle;
   }
}