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@mbostock
Last active April 3, 2024 10:25
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Force-Directed Tree
license: gpl-3.0
height: 960
redirect: https://observablehq.com/@d3/force-directed-tree

This randomly-generated tree is positioned using a force simulation.

<!DOCTYPE html>
<meta charset="utf-8">
<canvas width="960" height="960"></canvas>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>
var nodes = d3.range(1000).map(function(i) {
return {
index: i
};
});
var links = d3.range(nodes.length - 1).map(function(i) {
return {
source: Math.floor(Math.sqrt(i)),
target: i + 1
};
});
var simulation = d3.forceSimulation(nodes)
.force("charge", d3.forceManyBody())
.force("link", d3.forceLink(links).distance(20).strength(1))
.force("x", d3.forceX())
.force("y", d3.forceY())
.on("tick", ticked);
var canvas = document.querySelector("canvas"),
context = canvas.getContext("2d"),
width = canvas.width,
height = canvas.height;
d3.select(canvas)
.call(d3.drag()
.container(canvas)
.subject(dragsubject)
.on("start", dragstarted)
.on("drag", dragged)
.on("end", dragended));
function ticked() {
context.clearRect(0, 0, width, height);
context.save();
context.translate(width / 2, height / 2);
context.beginPath();
links.forEach(drawLink);
context.strokeStyle = "#aaa";
context.stroke();
context.beginPath();
nodes.forEach(drawNode);
context.fill();
context.strokeStyle = "#fff";
context.stroke();
context.restore();
}
function dragsubject() {
return simulation.find(d3.event.x - width / 2, d3.event.y - height / 2);
}
function dragstarted() {
if (!d3.event.active) simulation.alphaTarget(0.3).restart();
d3.event.subject.fx = d3.event.subject.x;
d3.event.subject.fy = d3.event.subject.y;
}
function dragged() {
d3.event.subject.fx = d3.event.x;
d3.event.subject.fy = d3.event.y;
}
function dragended() {
if (!d3.event.active) simulation.alphaTarget(0);
d3.event.subject.fx = null;
d3.event.subject.fy = null;
}
function drawLink(d) {
context.moveTo(d.source.x, d.source.y);
context.lineTo(d.target.x, d.target.y);
}
function drawNode(d) {
context.moveTo(d.x + 3, d.y);
context.arc(d.x, d.y, 3, 0, 2 * Math.PI);
}
</script>
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