!function(){
  tdad3 = {};

  tdad3.rips2d = _update;

  // data: array of points
  // radius: limiting radius of balls
  function _update(data, _radius) {

    var radius = _radius || -1;

    var delaunay = d3.geom.delaunay(data);
    var triangles = [];

    // Delete delaunay triangles whose edges would not exceed our
    // given radius, and return the rest of the triangles.
    delaunayLength = delaunay.length;
    for (var i = 0; i < delaunayLength; i++) {
        var triple = delaunay[i];
        var a = distanceBetween(triple[0], triple[1]);
        var b = distanceBetween(triple[0], triple[2]);
        var c = distanceBetween(triple[1], triple[2]);
        var max = Math.max(a, Math.max(b, c));
        if (radius == -1 || max < radius*2) {
            triangles.push(triple);
        }
    }

    return triangles;
  }

  function distanceBetween(a, b) {
    return Math.sqrt((a[0] - b[0]) * (a[0] - b[0]) + (a[1] - b[1]) * (a[1] - b[1]));
  }
}();