Connected Particles

A modification of Mike Bostock's Connected Particles. An exercise to become familiar with the canvas. Varied the circle size to give some element of depth, and turned the lines into curves.

<!DOCTYPE html>
<meta charset="utf-8">
<html>
<head>
    <title></title>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js" charset="utf-8"></script>
</head>
<body>
    <canvas width="1400" height="800"></canvas>
    <script type="text/javascript">
var canvas = document.querySelector("canvas"),
    context = canvas.getContext("2d"),
    width = canvas.width,
    height = canvas.height,
    radius = 2.5,
    minDistance = 20,
    maxDistance = 100,
    minDistance2 = minDistance * minDistance,
    maxDistance2 = maxDistance * maxDistance;

var tau = 2 * Math.PI,
    n = 1000,
    particles = new Array(n);

for (var i = 0; i < n; ++i){
    particles[i] = {
        x: width * Math.random(),
        y0: height * Math.random(),
        v: .1 * (Math.random() - .5)
    };
}

d3.timer(function(elapsed) {
    context.clearRect(0, 0, width, height);

for (var i = 0; i < n; ++i) {
        for (var j = i + 1; j < n; ++j) {
            var pi = particles[i],
                pj = particles[j],
                dx = pi.x - pj.x,
                dy = pi.y - pj.y,
                d2 = dx * dx + dy * dy;
            if (d2 < maxDistance2) {
                context.globalAlpha = d2 > minDistance2 ? (maxDistance2 - d2) / (maxDistance2 - minDistance2) : 1;
                context.beginPath();
                context.moveTo(pi.x, pi.y);
                context.quadraticCurveTo(
                    (pj.x - pi.x) / 2 + Math.min(pj.x, pi.x), 
                    (Math.max(pi.y, pj.y) - Math.min(pi.y, pj.y)) / 2 + Math.min(pj.y, pi.y) + 5, 
                    pj.x, 
                    pj.y);
                context.stroke();
            }
        }
    }
    context.globalAlpha = 0.8;

for (var i = 0; i < n; ++i) {
        var p = particles[i];
        p.y = p.y0 + elapsed * p.v;
        if (p.y > height + maxDistance) p.x = width * Math.random(), p.y0 -= height + 2 * maxDistance;
        else if (p.y < -maxDistance) p.x = width * Math.random(), p.y0 += height + 2 * maxDistance;
        context.beginPath();
        var scaleFactor = (p.v * 10 + 0.6) * 2.5;
        var dotRadius = p.v > 0 ? radius * scaleFactor : radius / scaleFactor;
        context.arc(p.x, p.y, dotRadius, 0, tau);
        context.fill();
    }
});
    </script>
</body>
</html>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js