Shape Objects

Creating simple shape objects.

This can simplify drawing to canvas:

ellipse.context(canvas).stroke();

It also lets you encapsulates geometry-related helper functions. For example, the parametric function of an ellipse mapping to Cartesian coordinates:

var point = ellipse.cartesian(theta); // point = {x, y}

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Shape Objects</title>
  </head>
  <body>
    <script src="//d3js.org/d3.v3.min.js" charset="utf-8"></script>
    <script src="shapes.js"></script>
    <script>
      var width = 960,
          height = 500,
          t0 = Date.now();

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

var context = canvas.node().getContext("2d");

var ellipse = shapes.ellipse().context(canvas.node());

var circles = d3.range(0, 2*Math.PI, 2*Math.PI/25)
        .map(function(t0) {
          return {
            t0: t0,
            shape: shapes.circle().context(canvas.node())
          };
        });

d3.timer(function() {
        var dt = Date.now() - t0,
            tick = dt/3000;

context.clearRect(0, 0, width, height);

ellipse
          .update(width/2, height/2, 400*Math.cos(tick), 200*Math.sin(tick))
          .stroke();

circles.forEach(function(circle) {
          var center = ellipse.cartesian(tick + circle.t0),
              radius = 5*Math.sin(tick + circle.t0) + 10;
          circle.shape
            .update(center.x, center.y, radius)
            .fill();
        });
      });
    </script>
  </body>
</html>

https://d3js.org/d3.v3.min.js