public void renderTree(){
    return renderTree(root);
  }

  private void renderTree(BspNode r){
    if(r != null) {

      int[] line = null;
      int i, result, nLines;

      nLines = r.lines.length;
      result = evalPoint(eye_x, eye_y, r.partition);
      if (result == IN_FRONT) {
        renderTree(r.back);
        for (i=0; i<nLines; i++){
          line = (int[])r.lines[i];
          if (evalPoint(eyeX, eyeY, getLineEquation(line)) == IN_FRONT)
            view3D.renderWall(line);
        }
        renderTree(r.front);
      } else if (result == IN_BACK) {
        renderTree(r.front);
        for (i=0; i<nLines; i++){
          line = (int[])r.lines[i];
          if (evalPoint(eyeX, eyeY, getLineEquation(line)) == IN_FRONT)
          view3D.renderWall(line);
        }
        renderTree(r.back);
      } else {   /* the eye is on the partition plane */
        renderTree(r.front);
        renderTree(r.back);
      }
    }
  }