Inertia dragging with versor II

Add inertia issue #27 to versor rotation of the globe.

Includes a modified versor.js, allowing the multiplication of the final rotation by a delta to the power alpha.

Moving average for velocity (exponential decay)

Trying to plug it in as cleanly as possible into d3.drag

Original research by Philippe Rivière for visionscarto.net.

Try it on mobile!

forked from Fil's block: Inertia dragging with versor

forked from earthjs's block: Inertia dragging with versor

<!DOCTYPE html>
<script src="https://d3js.org/topojson.v2.min.js"></script>
<script src="https://unpkg.com/d3"></script>
<script src="inertiaDrag.js"></script>
<script src="versor.js"></script>
<body>
	<canvas width="960" height="500"></canvas>
	<script>
		let land;
		const canvas = d3.select("canvas"),
		projection = d3.geoOrthographic(),
		context = canvas.node().getContext("2d"),
		path = d3.geoPath().projection(projection).context(context),
		render = function(r) {
      	r && projection.rotate(r);
				context.clearRect(0, 0, 960, 500);
				context.beginPath();
				path(land);
				context.fill();
		};          
    // complete params: (projection, render, startDrag, dragging, endDrag)
		const {start, move, end} = inertiaDrag(projection, render); 
		canvas.call(d3.drag().on("start", start)
								         .on("drag", move)
								         .on("end", end));
		d3.json("110m.json", function(error, world) {
			land = topojson.feature(world, world.objects.land);
			render();
		});
	</script>

https://d3js.org/topojson.v2.min.js

https://unpkg.com/d3