distanceBetween = ( a, b ) => {

	let dx = a.x - b.x,
		dy = a.y - b.y;

	return Math.sqrt( dx*dx + dy*dy );

}
Measures the distance in pixels between point a
and point b.

@param {object} a point with x/y properties
@param {object} b point with x/y properties

@return {number}