var vectorField = p => ({ x: -p.y, y: p.x });

streamlines({
  vectorField,
  onPointAdded(from, to) {
    // called when new point is added to a line
    console.log("point created", from, to);
  },
  onStreamlineAdded(points) {
    // Points is just a sequence of points with `x, y` coordinates through which
    // the streamline goes.
    console.log("stream line created. Number of points: ", points.length);
  }
}).run();

streamlines({
  // Vector field is a function that given a point p returns 2d vector
  // field {x, y}
  vectorField(p) { return p; },

  // Defines bounding box of the vector field
  boundingBox: {left: -5, top: -5, width: 10, height: 10},

  // Defines the first point where integration should start. If this is
  // not specified a random point inside boundingBox is selected
  // You can pass array of seed points, they are going to be used one by one
  // if they satisfy the rules.
  seed: {x: -1, y: 1},

  // Separation distance between new streamlines.
  dSep: 0.5

  // Distance between streamlines when integration should stop.
  dTest: 0.25,

  // Integration time step (passed to RK4 method.)
  timeStep: 0.01,

  // If set to true, lines are going to be drawn from the seed points
  // only in the direction of the vector field
  forwardOnly: false
}).run();

// Let's assume you have a <canvas id='scene'></canvas> in your document:
var canvas = document.getElementById("scene");

// Then you can render to it with this bit of code:
streamlines({
  // As usual, define your vector field:
  vectorField(p) {
    return { x: -p.y, y: p.x };
  },

  // And print the output to this canvas:
  onPointAdded: streamlines.renderTo(canvas)
}).run();

var renderer = streamlines({
  vectorField(p) {
    return p;
  }
});

// Launch the construction
renderer.run();

// something has happened and you want to stop?
renderer.dispose();