code: function computeTextRadius(lines) {
      var textRadius = 0;
  
      for (var i = 0, n = lines.length; i < n; ++i) {
          var dx = lines[i].width / 2;
          var dy = (Math.abs(i - n / 2 + 0.5) + 0.5) * DEFAULT_CANVAS_LINE_HEIGHT;
          textRadius = Math.max(textRadius, Math.sqrt(dx * dx + dy * dy));
      }
  
      return textRadius;
  }
docs: Compute the radius of the circle wrapping all the lines.
  
  @param lines array of text lines
  @return {number}