tree_filter = function(x, y, search, ...params) {
  var node = this._root
  var t = {x:x, y:y,
    	x0: this._x0,
      y0: this._y0,
      x3: this._x1,
      y3: this._y1,
      quads: [],
      node: node}

//   search.init(t, params)
  if (t.node) {t.quads.push(new Quad(t.node, t.x0, t.y0, t.x3, t.y3))};
  search.init(t, params)
  
	var i = 0;
  while (t.q = t.quads.pop()) {
    i++;
// 		console.log("q", t.q)
    // Stop searching if this quadrant can’t contain a closer node.
    if (!(t.node = t.q.node)
        || (t.x1 = t.q.x0) > t.x3
        || (t.y1 = t.q.y0) > t.y3
        || (t.x2 = t.q.x1) < t.x0
        || (t.y2 = t.q.y1) < t.y0) continue;

    // Bisect the current quadrant.
    if (t.node.length) {
      t.node.explored = true;
      var xm = (t.x1 + t.x2) / 2,
          ym = (t.y1 + t.y2) / 2;

      t.quads.push(
        new Quad(t.node[3], xm, ym, t.x2, t.y2),
        new Quad(t.node[2], t.x1, ym, xm, t.y2),
        new Quad(t.node[1], xm, t.y1, t.x2, ym),
        new Quad(t.node[0], t.x1, t.y1, xm, ym)
      );

      // Visit the closest quadrant first.
      if (t.i = (y >= ym) << 1 | (x >= xm)) {
        t.q = t.quads[t.quads.length - 1];
        t.quads[t.quads.length - 1] = t.quads[t.quads.length - 1 - t.i];
        t.quads[t.quads.length - 1 - t.i] = t.q;
      }
    }

    // Visit this point. (Visiting coincident points isn’t necessary!)
    else {
      var dx = x - +this._x.call(null, t.node.data),
          dy = y - +this._y.call(null, t.node.data),
          d2 = dx * dx + dy * dy;
      search.visit(t, d2);
    }
  }
// 	console.log("i", i);
  return t.result;
}