How to draw some own edges in node-link diagram in D3

Question

Drawing a single node link in a node-link diagram can be done as described here: D3 Power layout Self-tuning Node

What would you change if you need to draw multiple links on the same node?

I tried to add a “twist” to it, based on the number of existing own links. Given the code from the linked example, I made the following changes:

function tick() {
  link.attr("d", function(d) {
  var x1 = d.source.x,
  y1 = d.source.y,
  x2 = d.target.x,
  y2 = d.target.y,
  dx = x2 - x1,
  dy = y2 - y1,
  dr = Math.sqrt(dx * dx + dy * dy),

  // Defaults for normal edge.
  drx = dr,
  dry = dr,
  xRotation = 0, // degrees
  largeArc = 0, // 1 or 0
  sweep = 1; // 1 or 0

  // Self edge.
  if ( x1 === x2 && y1 === y2 ) {
    // Fiddle with this angle to get loop oriented.
    var index = getIndexOfDuplicateEdge();
    var degree = 360 / numberOfDuplicateEdges();
    var degreeForIndex = degree * index;


    xRotation = degreeForIndex; // Previously: -45;

    // Needs to be 1.
    largeArc = 1;

    // Change sweep to change orientation of loop. 
    //sweep = 0; // I also tried to change it based on index % 2 

    // Make drx and dry different to get an ellipse
    // instead of a circle.
    drx = 30;
    dry = 20;

    // For whatever reason the arc collapses to a point if the beginning
    // and ending points of the arc are the same, so kludge it.
    x2 = x2 + 1;
    y2 = y2 + 1;
  } 

 return "M" + x1 + "," + y1 + "A" + drx + "," + dry + " " + xRotation + "," + largeArc + "," + sweep + " " + x2 + "," + y2;
 }); 

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Answer 1

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, : ( , svg "svgthing" )

function radtodeg(angle) {
    return angle * (180/Math.PI);
}

function flower( center_x, center_y, num_self_edges, start_angle, end_angle, radius, length ) {

  var angle_sector = end_angle - start_angle;

  var num_points = num_self_edges * 2;

  var angle_per_point = angle_sector / num_points;
  var angle_per_sector = angle_per_point * 2;

  var str_builder = [];

  for( var angle = start_angle; angle < end_angle; angle += angle_per_sector ) {
    var start_sector_angle = angle;
    var end_sector_angle = angle + angle_per_point;

    var mid_sector_angle = angle + angle_per_point / 2;

    var start_x = center_x + (radius * Math.cos(start_sector_angle));
    var start_y = center_y + (radius * Math.sin(start_sector_angle));
    var end_x = center_x + (radius * Math.cos(end_sector_angle));
    var end_y = center_y + (radius * Math.sin(end_sector_angle));

    var mid_x = center_x + (radius * Math.cos(mid_sector_angle));
    var mid_y = center_y + (radius * Math.sin(mid_sector_angle));

      str_builder.push("<path d='");
    str_builder.push("M" + start_x + " " + start_y + ",");
    str_builder.push("A " + length + " 1 " + radtodeg(mid_sector_angle) + " 0 1 " + end_x + " " + end_y);
    str_builder.push("'/>\n");

    str_builder.push("<circle cx='" + start_x + "' cy='" + start_y + "' r='5' />\n");
    str_builder.push("<circle cx='" + end_x + "' cy='" + end_y + "' r='5'/>\n");
    str_builder.push("<circle cx='" + mid_x + "' cy='" + mid_y + "' r='5'/>\n");
  }

  str_builder.push("<circle cx='" + center_x + "' cy='" + center_y + "' r='" + radius + "' />\n");

  $("#svgthing").html(str_builder.join(""));
}

flower(60, 50, 8, 0, 2 * Math.PI, 50, 10);

8 .