Scale a Polygon by harrystevens

index.html

<!DOCTYPE html>
<html>
<head>
  <style>
    body {
      margin: 0;
      font-family: "Helvetica Neue", sans-serif;
    }
    .input-wrapper {
      padding: 10px;
      position: absolute;
    }
    polygon {
      fill: steelblue;
    }
  </style>
</head>
<body>
  <div class="input-wrapper">
    <div>
      Size: <span class="scale-factor">100%</span>
    </div>
    <input type="range" min="10" max="200" value="100" />
  </div>
  <script src="https://d3js.org/d3.v5.min.js"></script>
  <script src="https://unpkg.com/geometric@1.0.10/build/geometric.min.js"></script>
  <script>
    var width = window.innerWidth,
        height = window.innerHeight,
        center = [width / 2, height / 2],
        vertices = [
          [center[0] - 100, center[1] - 100],
          [center[0], center[1] - 130],
          [center[0] + 100, center[1] - 100],
          [center[0] + 150, center[1]],
          [center[0] + 100, center[1] + 100],
          [center[0], center[1] + 130],
          [center[0] - 100, center[1] + 100],
          [center[0] - 150, center[1]]
        ];

    var input = d3.select("input");

    var svg = d3.select("body").append("svg")
        .attr("width", width)
        .attr("height", height);

    var polygon = svg.append("polygon")
        .attr("points", vertices.join(" "));

    input.on("input", _ => {
      var scaleFactor = +input.property("value") / 100;
      var newVertices = geometric.polygonScale(vertices, scaleFactor);
      polygon.attr("points", newVertices.join(" "));
      d3.select(".scale-factor").text(Math.round(scaleFactor * 100) + "%");
    });
  </script>

</body>
</html>