d3.svg.diagonal.radial = function() {

  var diagonal = d3.svg.diagonal(),

      projection = d3_svg_diagonalProjection,

      projection_ = diagonal.projection;

  diagonal.projection = function(x) {

    return arguments.length

        ? projection_(d3_svg_diagonalRadialProjection(projection = x))

        : projection;

  };

  return diagonal;

};

function d3_svg_diagonalRadialProjection(projection) {

  return function() {

    var d = projection.apply(this, arguments),

        r = d[0],

        a = d[1] + d3_svg_arcOffset;

    return [r * Math.cos(a), r * Math.sin(a)];

  };

}