Connecting the dots...

Click to add nodes! Nodes near the cursor will be linked to the new node.

D3's force layout uses the Barnes–Hut approximation to compute repulsive charge forces between all nodes efficiently. Links are implemented as geometric constraints on top of position Verlet integration, offering greater stability. A virtual spring between each node and the center of the chart prevents nodes from drifting into space.

forked from mbostock's block: Build Your Own Graph!

forked from anonymous's block: Build Your Own Graph!

<!DOCTYPE html>
<meta charset="utf-8">
<style>

rect {
  fill: none;
  border: 1px;
  stroke: grey;
  pointer-events: all;
}

.node {
  fill: #111;
}

.cursor {
  fill: none;
  stroke: brown;
  pointer-events: none;
}

.link {
    fill:none;
    stroke: #DDD;
    stroke-width:0.5px;
}

.link2 {
  stroke: #999;
}
  
</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var width = 640,
    height = 640;
  
var size = 20;
  
var fill = d3.scale.category10();

var nodes = d3.range( size ).map(function(i) {
  return { id: i, x: Math.round(width*Math.random()), y: Math.round(height*Math.random()) };
});

console.log( 'nodes', nodes ); 
  
var nodeLinks = [];
d3.range( size * 1 ).map(function(i) {
// 	var isource = Math.round((size-1)*Math.random());
  var isource = i;
  
  var node = nodes[ isource ];
  console.log( 'isource', node, isource );

//   d3.range( 5 ).map(function(i) {
//   	var itarget = Math.round((size-1)*Math.random());
 
//   	nodeLinks.push({source: nodes[ isource ], target: nodes[ itarget ]});
// 	});

//   add links to any nearby nodes
  nodes.forEach(function(target, itarget) {
		console.log( 'foreach', target, itarget ); 
    var x = target.x - node.x,
        y = target.y - node.y;
    if (isource != itarget && Math.sqrt(x * x + y * y) < 120) {
	  	var existing = nodeLinks.filter( function(d, i) {
        console.log( 'filter', d, isource, itarget );
        return ( d.source == itarget && d.target == isource )
     })[0]; 
      console.log( 'existing?', existing );  
      if( existing === undefined ) { nodeLinks.push({source: isource, target: itarget}) };  
    }
  });
 
});

console.log( 'nodeLinks', nodeLinks );
  
var drag = d3.behavior.drag()
	.on("drag", function( d, i ) {
  	d.x += d3.event.dx
    d.y += d3.event.dy
    d3.select(this).attr("cx", d.x).attr("cy", d.y);
		var i = 0;
    links.each(function(l, li) {
			console.log( l, d, i );
      if (l.source == d.id) {
      	d3.select(this).attr("x1", d.x).attr("y1", d.y);
      } else if (l.target == d.id) {
      	d3.select(this).attr("x2", d.x).attr("y2", d.y);
      }
    });
  });
  
var link = d3.svg.line() 
   .x(function(d) { return d.x; })
   .y(function(d) { return d.y; })
   .interpolate("linear");

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);
  
svg.append("rect")
    .attr("width", width)
    .attr("height", height);

// svg.append("path")
//     .attr("d", link(nodes) )
//     .attr("class", "link");

// svg.selectAll(".link")
// 		.data( links )
// 	.enter().append("line")
//       .attr("class", "link")
// 			.attr("x1", function( d ) { return d.source.x } )
// 			.attr("y1", function( d ) { return d.source.y } )
// 			.attr("x2", function( d ) { return d.target.x } )
// 			.attr("y2", function( d ) { return d.target.y } );

console.log( links ); 
  
svg.selectAll(".node")
    .data(nodes)
  .enter()
  	.append("circle")
    .attr("class", "node")
    .attr("r", 4 )
	  .attr("cx", function(d) {
  	   return d.x
	   })
  	 .attr("cy", function(d) {
    	 return d.y
	   })
    .style("fill", function(d) { return fill(d.id); })
		.call(drag);
  
function transform(d) {
    return "translate(" + d.x + "," + d.y + ")";
}

</script>

https://d3js.org/d3.v3.min.js