Draggable Element Label

by Roman Bruckner

HTML

<html>
<head>
    <link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/jointjs/3.3.0/joint.css" />
</head>
<body>
      <!-- content -->
      <div id="paper"></div>

      <!-- dependencies -->
        <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.js"></script>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.20/lodash.min.js"></script>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/backbone.js/1.4.0/backbone.js"></script>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/jointjs/3.3.0/joint.js"></script>
    
    </body>
</html>

JavaScript

var GAP = 10;

var graph = new joint.dia.Graph;
var paper = new joint.dia.Paper({
  el: document.getElementById('paper'),
  width: 450,
  height: 300,
  model: graph,
  async: true,
  sorting: joint.dia.Paper.sorting.NONE,
  restrictTranslate: function(elementView, x0, y0) {

    var element = elementView.model;
    if (!element.get('label')) return;

    var parent = element.getParentCell();
    if (!parent) return;

    var bbox = element.getBBox();
    var parentBBox = parent.getBBox().inflate(GAP).moveAndExpand({
      x: -bbox.width,
      y: -bbox.height,
      width: bbox.width,
      height: bbox.height
    });

    return function(x, y) {
      var side = parentBBox.sideNearestToPoint({
        x,
        y
      });
      switch (side) {
        case 'right':
          return parentBBox.rightMiddle();
        case 'left':
          return parentBBox.leftMiddle();
        case 'bottom':
          return parentBBox.bottomMiddle();
        case 'top':
          return parentBBox.topMiddle();
      }
    };
  }
});

var rect = new joint.shapes.standard.Rectangle({
  size: {
    width: 100,
    height: 100
  },
  position: {
    x: 100,
    y: 100
  }
});

var label = new joint.shapes.standard.Rectangle({
  label: true,
  size: {
    width: 100,
    height: 30
  },
  position: {
    x: 100,
    y: 200 + GAP
  },
  attrs: {
    label: {
      text: 'Label',
      pointerEvents: 'all'
    },
    body: {
      pointerEvents: 'none',
      opacity: 0
    }
  }
});

graph.addCells([rect, label]);
rect.embed(label);
updateLabelAlignment(label);

graph.on('change:position', function(label, position, opt) {
  if (opt.translateBy !== label.id) return;
  if (!label.get('label')) return;
  updateLabelAlignment(label);
});

function updateLabelAlignment(label) {
  var parent = label.getParentCell();
  if (!parent) return;
  var bbox = label.getBBox();
  var parentBBox = parent.getBBox();
  var labelAttrs = {};
  // horizontal
  if (bbox.x < parentBBox.x) {
   ...