code: function generateArcPath (x, y, radius, startAngle, endAngle) {
    var start = polarToCartesian(x, y, radius, startAngle);
    var end = polarToCartesian(x, y, radius, endAngle);
    var arcSweep = endAngle - startAngle <= 180 ? '0' : '1';
    return [
      'M', start.x, start.y,
      'A', radius, radius, 0, arcSweep, 0, end.x, end.y
    ].join(' ');
  }
docs: generate d attribute value for ART <Shape>