Object selection is tough, particularly when the things you’d like to select are moving around (like nodes in a force-directed layout, perhaps). Allowing a user the fudge factor of an area cursor helps, but can get in the way when targets are small enough. The use of a Voronoi tessellation promises a map of closest node for any given point.
This example illustrates the use of a Voronoi overlay to clip nodes in a force-directed simulation. By using the Voronoi shapes as the clipping path the nodes themselves can be drawn much simpler.
This builds on these two examples from Mike Bostock on force-directed graphs and voronoi tesselation, as well as Nate Vack’s Voronoi selection example here and this first pass at an integration from Christopher Manning.
<html>
<head>
<style>
.node {
opacity: 0.5;
}
.node:hover {
opacity: 1;
}
.link {
stroke: #999;
stroke-opacity: 0.3;
}
</style>
<script src="//d3js.org/d3.v3.min.js"></script>
</head>
<body>
<div id="viz"></div>
<script>
function name(d) { return d.name; }
function group(d) { return d.group; }
var color = d3.scale.category10();
function colorByGroup(d) { return color(group(d)); }
var width = 960,
height = 500;
var svg = d3.select('#viz')
.append('svg')
.attr('width', width)
.attr('height', height);
var node, link;
var voronoi = d3.geom.voronoi()
.x(function(d) { return d.x; })
.y(function(d) { return d.y; })
.clipExtent([[-10, -10], [width+10, height+10]]);
function recenterVoronoi(nodes) {
var shapes = [];
voronoi(nodes).forEach(function(d) {
if ( !d.length ) return;
var n = [];
d.forEach(function(c){
n.push([ c[0] - d.point.x, c[1] - d.point.y ]);
});
n.point = d.point;
shapes.push(n);
});
return shapes;
}
var force = d3.layout.force()
.charge(-2000)
.friction(0.3)
.linkDistance(50)
.size([width, height]);
force.on('tick', function() {
node.attr('transform', function(d) { return 'translate('+d.x+','+d.y+')'; })
.attr('clip-path', function(d) { return 'url(#clip-'+d.index+')'; });
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; });
var clip = svg.selectAll('.clip')
.data( recenterVoronoi(node.data()), function(d) { return d.point.index; } );
clip.enter().append('clipPath')
.attr('id', function(d) { return 'clip-'+d.point.index; })
.attr('class', 'clip');
clip.exit().remove()
clip.selectAll('path').remove();
clip.append('path')
.attr('d', function(d) { return 'M'+d.join(',')+'Z'; });
});
d3.json('miserables.json', function(err, data) {
data.nodes.forEach(function(d, i) {
d.id = i;
});
link = svg.selectAll('.link')
.data( data.links )
.enter().append('line')
.attr('class', 'link')
.style("stroke-width", function(d) { return Math.sqrt(d.value); });
node = svg.selectAll('.node')
.data( data.nodes )
.enter().append('g')
.attr('title', name)
.attr('class', 'node')
.call( force.drag );
node.append('circle')
.attr('r', 30)
.attr('fill', colorByGroup)
.attr('fill-opacity', 0.5);
node.append('circle')
.attr('r', 4)
.attr('stroke', 'black');
force
.nodes( data.nodes )
.links( data.links )
.start();
});
</script>
</body>
</html>{
"nodes":[
{"name":"Myriel","group":1},
{"name":"Napoleon","group":1},
{"name":"Mlle.Baptistine","group":1},
{"name":"Mme.Magloire","group":1},
{"name":"CountessdeLo","group":1},
{"name":"Geborand","group":1},
{"name":"Champtercier","group":1},
{"name":"Cravatte","group":1},
{"name":"Count","group":1},
{"name":"OldMan","group":1},
{"name":"Labarre","group":2},
{"name":"Valjean","group":2},
{"name":"Marguerite","group":3},
{"name":"Mme.deR","group":2},
{"name":"Isabeau","group":2},
{"name":"Gervais","group":2},
{"name":"Tholomyes","group":3},
{"name":"Listolier","group":3},
{"name":"Fameuil","group":3},
{"name":"Blacheville","group":3},
{"name":"Favourite","group":3},
{"name":"Dahlia","group":3},
{"name":"Zephine","group":3},
{"name":"Fantine","group":3},
{"name":"Mme.Thenardier","group":4},
{"name":"Thenardier","group":4},
{"name":"Cosette","group":5},
{"name":"Javert","group":4},
{"name":"Fauchelevent","group":0},
{"name":"Bamatabois","group":2},
{"name":"Perpetue","group":3},
{"name":"Simplice","group":2},
{"name":"Scaufflaire","group":2},
{"name":"Woman1","group":2},
{"name":"Judge","group":2},
{"name":"Champmathieu","group":2},
{"name":"Brevet","group":2},
{"name":"Chenildieu","group":2},
{"name":"Cochepaille","group":2},
{"name":"Pontmercy","group":4},
{"name":"Boulatruelle","group":6},
{"name":"Eponine","group":4},
{"name":"Anzelma","group":4},
{"name":"Woman2","group":5},
{"name":"MotherInnocent","group":0},
{"name":"Gribier","group":0},
{"name":"Jondrette","group":7},
{"name":"Mme.Burgon","group":7},
{"name":"Gavroche","group":8},
{"name":"Gillenormand","group":5},
{"name":"Magnon","group":5},
{"name":"Mlle.Gillenormand","group":5},
{"name":"Mme.Pontmercy","group":5},
{"name":"Mlle.Vaubois","group":5},
{"name":"Lt.Gillenormand","group":5},
{"name":"Marius","group":8},
{"name":"BaronessT","group":5},
{"name":"Mabeuf","group":8},
{"name":"Enjolras","group":8},
{"name":"Combeferre","group":8},
{"name":"Prouvaire","group":8},
{"name":"Feuilly","group":8},
{"name":"Courfeyrac","group":8},
{"name":"Bahorel","group":8},
{"name":"Bossuet","group":8},
{"name":"Joly","group":8},
{"name":"Grantaire","group":8},
{"name":"MotherPlutarch","group":9},
{"name":"Gueulemer","group":4},
{"name":"Babet","group":4},
{"name":"Claquesous","group":4},
{"name":"Montparnasse","group":4},
{"name":"Toussaint","group":5},
{"name":"Child1","group":10},
{"name":"Child2","group":10},
{"name":"Brujon","group":4},
{"name":"Mme.Hucheloup","group":8}
],
"links":[
{"source":1,"target":0,"value":1},
{"source":2,"target":0,"value":8},
{"source":3,"target":0,"value":10},
{"source":3,"target":2,"value":6},
{"source":4,"target":0,"value":1},
{"source":5,"target":0,"value":1},
{"source":6,"target":0,"value":1},
{"source":7,"target":0,"value":1},
{"source":8,"target":0,"value":2},
{"source":9,"target":0,"value":1},
{"source":11,"target":10,"value":1},
{"source":11,"target":3,"value":3},
{"source":11,"target":2,"value":3},
{"source":11,"target":0,"value":5},
{"source":12,"target":11,"value":1},
{"source":13,"target":11,"value":1},
{"source":14,"target":11,"value":1},
{"source":15,"target":11,"value":1},
{"source":17,"target":16,"value":4},
{"source":18,"target":16,"value":4},
{"source":18,"target":17,"value":4},
{"source":19,"target":16,"value":4},
{"source":19,"target":17,"value":4},
{"source":19,"target":18,"value":4},
{"source":20,"target":16,"value":3},
{"source":20,"target":17,"value":3},
{"source":20,"target":18,"value":3},
{"source":20,"target":19,"value":4},
{"source":21,"target":16,"value":3},
{"source":21,"target":17,"value":3},
{"source":21,"target":18,"value":3},
{"source":21,"target":19,"value":3},
{"source":21,"target":20,"value":5},
{"source":22,"target":16,"value":3},
{"source":22,"target":17,"value":3},
{"source":22,"target":18,"value":3},
{"source":22,"target":19,"value":3},
{"source":22,"target":20,"value":4},
{"source":22,"target":21,"value":4},
{"source":23,"target":16,"value":3},
{"source":23,"target":17,"value":3},
{"source":23,"target":18,"value":3},
{"source":23,"target":19,"value":3},
{"source":23,"target":20,"value":4},
{"source":23,"target":21,"value":4},
{"source":23,"target":22,"value":4},
{"source":23,"target":12,"value":2},
{"source":23,"target":11,"value":9},
{"source":24,"target":23,"value":2},
{"source":24,"target":11,"value":7},
{"source":25,"target":24,"value":13},
{"source":25,"target":23,"value":1},
{"source":25,"target":11,"value":12},
{"source":26,"target":24,"value":4},
{"source":26,"target":11,"value":31},
{"source":26,"target":16,"value":1},
{"source":26,"target":25,"value":1},
{"source":27,"target":11,"value":17},
{"source":27,"target":23,"value":5},
{"source":27,"target":25,"value":5},
{"source":27,"target":24,"value":1},
{"source":27,"target":26,"value":1},
{"source":28,"target":11,"value":8},
{"source":28,"target":27,"value":1},
{"source":29,"target":23,"value":1},
{"source":29,"target":27,"value":1},
{"source":29,"target":11,"value":2},
{"source":30,"target":23,"value":1},
{"source":31,"target":30,"value":2},
{"source":31,"target":11,"value":3},
{"source":31,"target":23,"value":2},
{"source":31,"target":27,"value":1},
{"source":32,"target":11,"value":1},
{"source":33,"target":11,"value":2},
{"source":33,"target":27,"value":1},
{"source":34,"target":11,"value":3},
{"source":34,"target":29,"value":2},
{"source":35,"target":11,"value":3},
{"source":35,"target":34,"value":3},
{"source":35,"target":29,"value":2},
{"source":36,"target":34,"value":2},
{"source":36,"target":35,"value":2},
{"source":36,"target":11,"value":2},
{"source":36,"target":29,"value":1},
{"source":37,"target":34,"value":2},
{"source":37,"target":35,"value":2},
{"source":37,"target":36,"value":2},
{"source":37,"target":11,"value":2},
{"source":37,"target":29,"value":1},
{"source":38,"target":34,"value":2},
{"source":38,"target":35,"value":2},
{"source":38,"target":36,"value":2},
{"source":38,"target":37,"value":2},
{"source":38,"target":11,"value":2},
{"source":38,"target":29,"value":1},
{"source":39,"target":25,"value":1},
{"source":40,"target":25,"value":1},
{"source":41,"target":24,"value":2},
{"source":41,"target":25,"value":3},
{"source":42,"target":41,"value":2},
{"source":42,"target":25,"value":2},
{"source":42,"target":24,"value":1},
{"source":43,"target":11,"value":3},
{"source":43,"target":26,"value":1},
{"source":43,"target":27,"value":1},
{"source":44,"target":28,"value":3},
{"source":44,"target":11,"value":1},
{"source":45,"target":28,"value":2},
{"source":47,"target":46,"value":1},
{"source":48,"target":47,"value":2},
{"source":48,"target":25,"value":1},
{"source":48,"target":27,"value":1},
{"source":48,"target":11,"value":1},
{"source":49,"target":26,"value":3},
{"source":49,"target":11,"value":2},
{"source":50,"target":49,"value":1},
{"source":50,"target":24,"value":1},
{"source":51,"target":49,"value":9},
{"source":51,"target":26,"value":2},
{"source":51,"target":11,"value":2},
{"source":52,"target":51,"value":1},
{"source":52,"target":39,"value":1},
{"source":53,"target":51,"value":1},
{"source":54,"target":51,"value":2},
{"source":54,"target":49,"value":1},
{"source":54,"target":26,"value":1},
{"source":55,"target":51,"value":6},
{"source":55,"target":49,"value":12},
{"source":55,"target":39,"value":1},
{"source":55,"target":54,"value":1},
{"source":55,"target":26,"value":21},
{"source":55,"target":11,"value":19},
{"source":55,"target":16,"value":1},
{"source":55,"target":25,"value":2},
{"source":55,"target":41,"value":5},
{"source":55,"target":48,"value":4},
{"source":56,"target":49,"value":1},
{"source":56,"target":55,"value":1},
{"source":57,"target":55,"value":1},
{"source":57,"target":41,"value":1},
{"source":57,"target":48,"value":1},
{"source":58,"target":55,"value":7},
{"source":58,"target":48,"value":7},
{"source":58,"target":27,"value":6},
{"source":58,"target":57,"value":1},
{"source":58,"target":11,"value":4},
{"source":59,"target":58,"value":15},
{"source":59,"target":55,"value":5},
{"source":59,"target":48,"value":6},
{"source":59,"target":57,"value":2},
{"source":60,"target":48,"value":1},
{"source":60,"target":58,"value":4},
{"source":60,"target":59,"value":2},
{"source":61,"target":48,"value":2},
{"source":61,"target":58,"value":6},
{"source":61,"target":60,"value":2},
{"source":61,"target":59,"value":5},
{"source":61,"target":57,"value":1},
{"source":61,"target":55,"value":1},
{"source":62,"target":55,"value":9},
{"source":62,"target":58,"value":17},
{"source":62,"target":59,"value":13},
{"source":62,"target":48,"value":7},
{"source":62,"target":57,"value":2},
{"source":62,"target":41,"value":1},
{"source":62,"target":61,"value":6},
{"source":62,"target":60,"value":3},
{"source":63,"target":59,"value":5},
{"source":63,"target":48,"value":5},
{"source":63,"target":62,"value":6},
{"source":63,"target":57,"value":2},
{"source":63,"target":58,"value":4},
{"source":63,"target":61,"value":3},
{"source":63,"target":60,"value":2},
{"source":63,"target":55,"value":1},
{"source":64,"target":55,"value":5},
{"source":64,"target":62,"value":12},
{"source":64,"target":48,"value":5},
{"source":64,"target":63,"value":4},
{"source":64,"target":58,"value":10},
{"source":64,"target":61,"value":6},
{"source":64,"target":60,"value":2},
{"source":64,"target":59,"value":9},
{"source":64,"target":57,"value":1},
{"source":64,"target":11,"value":1},
{"source":65,"target":63,"value":5},
{"source":65,"target":64,"value":7},
{"source":65,"target":48,"value":3},
{"source":65,"target":62,"value":5},
{"source":65,"target":58,"value":5},
{"source":65,"target":61,"value":5},
{"source":65,"target":60,"value":2},
{"source":65,"target":59,"value":5},
{"source":65,"target":57,"value":1},
{"source":65,"target":55,"value":2},
{"source":66,"target":64,"value":3},
{"source":66,"target":58,"value":3},
{"source":66,"target":59,"value":1},
{"source":66,"target":62,"value":2},
{"source":66,"target":65,"value":2},
{"source":66,"target":48,"value":1},
{"source":66,"target":63,"value":1},
{"source":66,"target":61,"value":1},
{"source":66,"target":60,"value":1},
{"source":67,"target":57,"value":3},
{"source":68,"target":25,"value":5},
{"source":68,"target":11,"value":1},
{"source":68,"target":24,"value":1},
{"source":68,"target":27,"value":1},
{"source":68,"target":48,"value":1},
{"source":68,"target":41,"value":1},
{"source":69,"target":25,"value":6},
{"source":69,"target":68,"value":6},
{"source":69,"target":11,"value":1},
{"source":69,"target":24,"value":1},
{"source":69,"target":27,"value":2},
{"source":69,"target":48,"value":1},
{"source":69,"target":41,"value":1},
{"source":70,"target":25,"value":4},
{"source":70,"target":69,"value":4},
{"source":70,"target":68,"value":4},
{"source":70,"target":11,"value":1},
{"source":70,"target":24,"value":1},
{"source":70,"target":27,"value":1},
{"source":70,"target":41,"value":1},
{"source":70,"target":58,"value":1},
{"source":71,"target":27,"value":1},
{"source":71,"target":69,"value":2},
{"source":71,"target":68,"value":2},
{"source":71,"target":70,"value":2},
{"source":71,"target":11,"value":1},
{"source":71,"target":48,"value":1},
{"source":71,"target":41,"value":1},
{"source":71,"target":25,"value":1},
{"source":72,"target":26,"value":2},
{"source":72,"target":27,"value":1},
{"source":72,"target":11,"value":1},
{"source":73,"target":48,"value":2},
{"source":74,"target":48,"value":2},
{"source":74,"target":73,"value":3},
{"source":75,"target":69,"value":3},
{"source":75,"target":68,"value":3},
{"source":75,"target":25,"value":3},
{"source":75,"target":48,"value":1},
{"source":75,"target":41,"value":1},
{"source":75,"target":70,"value":1},
{"source":75,"target":71,"value":1},
{"source":76,"target":64,"value":1},
{"source":76,"target":65,"value":1},
{"source":76,"target":66,"value":1},
{"source":76,"target":63,"value":1},
{"source":76,"target":62,"value":1},
{"source":76,"target":48,"value":1},
{"source":76,"target":58,"value":1}
]
}