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Isolating Forces
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.block
license: gpl-3.0
Raw
README.md

This example demonstrates how to patch force.initialize such that a force applies only to a subset of nodes in a simulation.

function isolate(force, filter) {
  var initialize = force.initialize;
  force.initialize = function() { initialize.call(force, nodes.filter(filter)); };
  return force;
}

Another way of having forces only apply to some nodes is to set the force strength to zero for those nodes by using a custom strength accessor (e.g., x.x). But if you have lots of isolated forces and lots of nodes, it is faster to isolate the force to a subset of nodes than to set the strength to zero for unaffected nodes.

Raw
index.html
<!DOCTYPE html>
<meta charset="utf-8">
<canvas width="960" height="500"></canvas>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>
var n = 20;
var nodes = d3.range(n * n).map(function(i) {
return {
index: i,
color: i < 200 ? "brown" : "steelblue"
};
});
var canvas = document.querySelector("canvas"),
context = canvas.getContext("2d"),
width = canvas.width,
height = canvas.height;
var simulation = d3.forceSimulation(nodes)
.force("y", d3.forceY())
.force("brown", isolate(d3.forceX(-width / 6), function(d) { return d.color === "brown"; }))
.force("steelblue", isolate(d3.forceX(width / 6), function(d) { return d.color === "steelblue"; }))
.force("charge", d3.forceManyBody().strength(-10))
.on("tick", ticked);
function ticked() {
context.clearRect(0, 0, width, height);
context.save();
context.translate(width / 2, height / 2);
nodes.forEach(drawNode);
context.restore();
}
function drawNode(d) {
context.beginPath();
context.moveTo(d.x + 3, d.y);
context.arc(d.x, d.y, 3, 0, 2 * Math.PI);
context.fillStyle = d.color;
context.fill();
}
function isolate(force, filter) {
var initialize = force.initialize;
force.initialize = function() { initialize.call(force, nodes.filter(filter)); };
return force;
}
</script>
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