The black dots show the midpoint computed by d3-shape’s arc.centroid. Note that this is not the geometric center of the arc, which may be outside the arc; this method is merely a convenience for positioning labels.
Last active
July 21, 2019 15:43
Donut Centroid
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| license: gpl-3.0 | |
| redirect: https://observablehq.com/@d3/donut-chart |
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| <!DOCTYPE html> | |
| <meta charset="utf-8"> | |
| <canvas width="960" height="500"></canvas> | |
| <script src="//d3js.org/d3.v4.0.0-alpha.4.min.js"></script> | |
| <script> | |
| var data = [1, 1, 2, 3, 5, 8, 13]; | |
| var canvas = document.querySelector("canvas"), | |
| context = canvas.getContext("2d"); | |
| var width = canvas.width, | |
| height = canvas.height, | |
| radius = Math.min(width, height) / 2; | |
| var colors = [ | |
| "#1f77b4", "#ff7f0e", "#2ca02c", "#d62728", "#9467bd", | |
| "#8c564b", "#e377c2", "#7f7f7f", "#bcbd22", "#17becf" | |
| ]; | |
| var arc = d3.arc() | |
| .outerRadius(radius - 10) | |
| .innerRadius(radius - 70) | |
| .context(context); | |
| var dot = d3.symbol() | |
| .context(context); | |
| var pie = d3.pie(); | |
| var arcs = pie(data); | |
| context.translate(width / 2, height / 2); | |
| context.globalAlpha = 0.5; | |
| arcs.forEach(function(d, i) { | |
| context.beginPath(); | |
| arc(d); | |
| context.fillStyle = colors[i]; | |
| context.fill(); | |
| }); | |
| context.globalAlpha = 1; | |
| context.beginPath(); | |
| arcs.forEach(arc); | |
| context.lineWidth = 1.5; | |
| context.stroke(); | |
| context.beginPath(); | |
| arcs.forEach(function(d) { | |
| var c = arc.centroid(d); | |
| context.save(); | |
| context.translate(c[0], c[1]); | |
| dot(); | |
| context.restore(); | |
| }); | |
| context.fillStyle = "#000"; | |
| context.fill(); | |
| </script> |
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