chart = {
const context = DOM.context2d(width, height);
const canvas = context.canvas;
// An assortment of randomly-positioned colorful circles.
const circles = d3.range(20).map(i => ({
x: Math.random() * (width - radius * 2) + radius,
y: Math.random() * (height - radius * 2) + radius,
color: d3.schemeCategory10[i % 10]
}));
// Whenever the circles move, redraw the canvas.
function render() {
context.clearRect(0, 0, width, height);
for (const {x, y, color, active} of circles) {
context.beginPath();
context.moveTo(x + radius, y);
context.arc(x, y, radius, 0, 2 * Math.PI);
context.fillStyle = color;
context.fill();
if (active) {
context.lineWidth = 2;
context.stroke();
}
}
}
// Bind the drag behavior for interaction.
d3.select(context.canvas).call(drag(circles)
.on("start.render drag.render end.render", render));
// Render the initial canvas.
render();
return canvas;
}
drag = circles => {
// Choose the circle that is closest to the pointer for dragging.
function dragsubject(event) {
let subject = null;
let distance = maxDistance;
for (const c of circles) {
let d = Math.hypot(event.x - c.x, event.y - c.y);
if (d < distance) {
distance = d;
subject = c;
}
}
return subject;
}
// When starting a drag gesture, move the subject to the top and mark it as active.
function dragstarted({subject}) {
circles.splice(circles.indexOf(subject), 1);
circles.push(subject);
subject.active = true;
}
// When dragging, update the subject’s position.
function dragged(event) {
event.subject.x = event.x;
event.subject.y = event.y;
}
// When ending a drag gesture, mark the subject as inactive again.
function dragended({subject}) {
subject.active = false;
}
return d3.drag()
.subject(dragsubject)
.on("start", dragstarted)
.on("drag", dragged)
.on("end", dragended);
}
maxDistance = Infinity // Limit the search distance, if desired.
height = 600
radius = 32
Purpose-built for displays of data
Observable is your go-to platform for exploring data and creating expressive data visualizations. Use reactive JavaScript notebooks for prototyping and a collaborative canvas for visual data exploration and dashboard creation.
