public ArrayList getPointList(long handId) {
   ArrayList curList;
   if (_pointLists.containsKey(handId)) curList = (ArrayList) _pointLists.get(handId);
   else {
     curList = new ArrayList(_maxPoints);
     _pointLists.put(handId, curList);
   }
   return curList;
 }
    public void draw() {
      if (_pointLists.size() <= 0) return;

      pushStyle();
      noFill();

      PVector vec;
      PVector firstVec;
      PVector screenPos = new PVector();
      int colorIndex = 0;

      // draw the hand lists
      Iterator<Map.Entry> itrList = _pointLists.entrySet().iterator();
      while (itrList.hasNext()) {
        strokeWeight(2);
        stroke(_colorList[colorIndex % (_colorList.length - 1)]);

        ArrayList curList = (ArrayList) itrList.next().getValue();

        // draw line
        firstVec = null;
        Iterator<PVector> itr = curList.iterator();
        beginShape();
        while (itr.hasNext()) {
          vec = itr.next();
          if (firstVec == null) firstVec = vec;
          // calc the screen pos
          context.convertRealWorldToProjective(vec, screenPos);
          vertex(screenPos.x, screenPos.y);
        }
        endShape();

        // draw current pos of the hand
        if (firstVec != null) {
          strokeWeight(8);
          context.convertRealWorldToProjective(firstVec, screenPos);
          point(screenPos.x, screenPos.y);
        }
        colorIndex++;
      }

      popStyle();
    }
    public void OnPointDestroy(long nID) {
      println("OnPointDestroy, handId: " + nID);

      // remove list
      if (_pointLists.containsKey(nID)) _pointLists.remove(nID);
    }