Circles bouncing inside a rectangle

Example for the Stackoverflow question: How can I contain D3 JS animation within a container

The balls use a modified version of the D3.js Force Layout. Parts of the code, such as the collision function are taken from Mike Bostock's example Multi-Foci Force Layout.

<!DOCTYPE html>
<meta charset="utf-8">
 
<body>
<script src="https://d3js.org/d3.v3.js"></script>
<script>
//Based in
///https://bl.ocks.org/mbostock/1804919
var margin = {top: 0, right: 0, bottom: 0, left: 0},
width = 960 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom;
 
var rect = [50,50, width - 50, height - 50];
 
var n = 20,
m = 4,
padding = 6,
maxSpeed = 3,
radius = d3.scale.sqrt().range([0, 8]),
color = d3.scale.category10().domain(d3.range(m));
var nodes = [];
 
for (i in d3.range(n)){
nodes.push({radius: radius(1 + Math.floor(Math.random() * 4)),
color: color(Math.floor(Math.random() * m)),
x: rect[0] + (Math.random() * (rect[2] - rect[0])),
y:rect[1] + (Math.random() * (rect[3] - rect[1])),
speedX: (Math.random() - 0.5) * 2 *maxSpeed,
speedY: (Math.random() - 0.5) * 2 *maxSpeed});
}
 
 
var force = d3.layout.force()
.nodes(nodes)
.size([width, height])
.gravity(0)
.charge(0)
.on("tick", tick)
.start();
 
var svg = d3.select("body").append("svg")
.attr("width", width + margin.left + margin.right)
.attr("height", height + margin.top + margin.bottom)
.append("g")
.attr("transform", "translate(" + margin.left + "," + margin.top + ")");
 
svg.append("svg:rect")
.attr("width", rect[2] - rect[0])
.attr("height", rect[3] - rect[1])
.attr("x", rect[0])
.attr("y", rect[1])
.style("fill", "None")
.style("stroke", "#222222");
 
var circle = svg.selectAll("circle")
.data(nodes)
.enter().append("circle")
.attr("r", function(d) { return d.radius; })
.attr("cx", function(d) { return d.x; })
.attr("cy", function(d) { return d.y; })
.style("fill", function(d) { return d.color; })
.call(force.drag);
 
var flag = false;
function tick(e) {
force.alpha(0.1)
circle
.each(gravity(e.alpha))
.each(collide(.5))
.attr("cx", function(d) { return d.x; })
.attr("cy", function(d) { return d.y; });
}
 
 
 
// Move nodes toward cluster focus.
function gravity(alpha) {
return function(d) {
if ((d.x - d.radius - 2) < rect[0]) d.speedX = Math.abs(d.speedX);
if ((d.x + d.radius + 2) > rect[2]) d.speedX = -1 * Math.abs(d.speedX);
if ((d.y - d.radius - 2) < rect[1]) d.speedY = -1 * Math.abs(d.speedY);
if ((d.y + d.radius + 2) > rect[3]) d.speedY = Math.abs(d.speedY);
 
d.x = d.x + (d.speedX * alpha);
d.y = d.y + (-1 * d.speedY * alpha);
 
};
}
 
// Resolve collisions between nodes.
function collide(alpha) {
var quadtree = d3.geom.quadtree(nodes);
return function(d) {
var r = d.radius + radius.domain()[1] + padding,
nx1 = d.x - r,
nx2 = d.x + r,
ny1 = d.y - r,
ny2 = d.y + r;
quadtree.visit(function(quad, x1, y1, x2, y2) {
if (quad.point && (quad.point !== d)) {
var x = d.x - quad.point.x,
y = d.y - quad.point.y,
l = Math.sqrt(x * x + y * y),
r = d.radius + quad.point.radius + (d.color !== quad.point.color) * padding;
if (l < r) {
l = (l - r) / l * alpha;
d.x -= x *= l;
d.y -= y *= l;
quad.point.x += x;
quad.point.y += y;
}
}
return x1 > nx2
|| x2 < nx1
|| y1 > ny2
|| y2 < ny1;
});
};
}
 
</script>

Modified http://d3js.org/d3.v3.js to a secure url

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