Circle Dragging I

This example demonstrates applying d3.drag for dragging circles in SVG. Each circle’s datum is an object with x and y properties. The data and the circle element’s position are updated during the drag event. The circle is raised to the foreground at the start of a drag, and a temporary stroke is applied during drag for visual feedback.

Compare this to dragging Canvas circles. Selection can be improved using a Voronoi overlay.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.active {
  stroke: #000;
  stroke-width: 2px;
}

</style>
<svg width="960" height="500"></svg>
<script src="//d3js.org/d3.v4.min.js"></script>
<script>

var svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height"),
    radius = 32;

var circles = d3.range(20).map(function() {
  return {
    x: Math.round(Math.random() * (width - radius * 2) + radius),
    y: Math.round(Math.random() * (height - radius * 2) + radius)
  };
});

var color = d3.scaleOrdinal()
    .range(d3.schemeCategory20);

svg.selectAll("circle")
  .data(circles)
  .enter().append("circle")
    .attr("cx", function(d) { return d.x; })
    .attr("cy", function(d) { return d.y; })
    .attr("r", radius)
    .style("fill", function(d, i) { return color(i); })
    .call(d3.drag()
        .on("start", dragstarted)
        .on("drag", dragged)
        .on("end", dragended));

function dragstarted(d) {
  d3.select(this).raise().classed("active", true);
}

function dragged(d) {
  d3.select(this).attr("cx", d.x = d3.event.x).attr("cy", d.y = d3.event.y);
}

function dragended(d) {
  d3.select(this).classed("active", false);
}

</script>

https://d3js.org/d3.v4.min.js