Rounded Rectangle by mbostock

index.html

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

body {
  margin: auto;
  width: 960px;
}

path {
  fill: #ccc;
  stroke: #000;
  stroke-width: 1.5px;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var svg = d3.select("body").append("svg")
    .attr("width", 960)
    .attr("height", 500)
  .append("g")
    .attr("transform", "translate(480,250)");

var rect = svg.append("path")
    .attr("d", rightRoundedRect(-240, -120, 480, 240, 20));

// Returns path data for a rectangle with rounded right corners.
// Note: it’s probably easier to use a <rect> element with rx and ry attributes!
// The top-left corner is ⟨x,y⟩.
function rightRoundedRect(x, y, width, height, radius) {
  return "M" + x + "," + y
       + "h" + (width - radius)
       + "a" + radius + "," + radius + " 0 0 1 " + radius + "," + radius
       + "v" + (height - 2 * radius)
       + "a" + radius + "," + radius + " 0 0 1 " + -radius + "," + radius
       + "h" + (radius - width)
       + "z";
}

</script>