Converting Collision Detection example to from v3 to v4 (D3)

Question

I'm trying to convert the Collision Detection example https://bl.ocks.org/mbostock/3231298

to D3 V4.

I've converted the force, but I can't get it to work. Can anyone point out what I'm doing wrong?

Thanks

var width = window.innerWidth
    var height = window.innerHeight

    var nodes = d3.range(200).map(function() { return {radius: Math.random() * 12 + 4}; }),
        root = nodes[0];
    var color = d3.scaleOrdinal().range(d3.schemeCategory20)

    root.radius = 0;
    root.fixed = true;

    const forceX = d3.forceX(width / 2).strength(0.015)
    const forceY = d3.forceY(height / 2).strength(0.015)

    var force = d3.forceSimulation()
        .force('x', forceX)
        .force('y',  forceY)
        .force('charge', function(d, i) { return i ? 0 : -2000; })
        .on('tick', ticked)
        .nodes(nodes);

    // var force = d3.layout.force()
    //     .gravity(0.05)
    //     .charge(function(d, i) { return i ? 0 : -2000; })
    //     .nodes(nodes)
    //     .size([width, height]);


    // force.start();

    var svg = d3.select(ctr)
        .attr("width", width)
        .attr("height", height);

    svg.selectAll("circle")
        .data(nodes.slice(1))
        .enter().append("circle")
        .attr("r", function(d) { return d.radius; })
        .style("fill", function(d, i) { return color(i % 3); });

    function ticked(e) {
        var q = d3.quadtree(nodes),
            i = 0,
            n = nodes.length;

        while (++i < n) q.visit(collide(nodes[i]));

        svg.selectAll("circle")
            .attr("cx", function(d) { return d.x; })
            .attr("cy", function(d) { return d.y; });
    };

    svg.on("mousemove", function() {
        var p1 = d3.mouse(this);
        root.px = p1[0];
        root.py = p1[1];
        force.restart();
    });

    function collide(node) {
        var r = node.radius + 16,
            nx1 = node.x - r,
            nx2 = node.x + r,
            ny1 = node.y - r,
            ny2 = node.y + r;
        return function(quad, x1, y1, x2, y2) {
            if (quad.point && (quad.point !== node)) {
                var x = node.x - quad.point.x,
                    y = node.y - quad.point.y,
                    l = Math.sqrt(x * x + y * y),
                    r = node.radius + quad.point.radius;
                if (l < r) {
                    l = (l - r) / l * .5;
                    node.x -= x *= l;
                    node.y -= y *= l;
                    quad.point.x += x;
                    quad.point.y += y;
                }
            }
            return x1 > nx2 || x2 < nx1 || y1 > ny2 || y2 < ny1;
        };
    }

Answer 1

This is my first ever answer on SO, so anyone who comes after me, feel free to nudge me in the proper direction. That being said, I was also interested in this, so here is my explanation:

Forcesimulation now provides a force called "collide", which should entirely replace the collide function in the v3 example:

.force("collide", d3.forceCollide().radius(function(d)
        {
            if(d === root){
                return Math.random() * 50 + 100;
            }
            return d.r + 0.5;
        }).iterations(5))

So, the entire simulation now looks like:

    var simulation = d3.forceSimulation()
        .velocityDecay(0.2)
        .force("x", d3.forceX(width / 2).strength(0.015))
        .force("y", d3.forceY(height / 2).strength(0.015))
        .force("collide", d3.forceCollide().radius(function(d)
        {
            if(d === root){
                return Math.random() * 50 + 100;
            }
            return d.r + 0.5;
        }).iterations(5))
        .nodes(nodes);

There are some other small things you are missing, such as fixing the position of the first node (our mouse controlled one) with:

        var p1 = d3.mouse(this);
        root.fx = p1[0];
        root.fy = p1[1];

Working example: https://jsfiddle.net/akLhhgzr/