Rotate 2D points

rotate-points.js

/**
 * rotate points around an origin
 * @param  {Array<object>} ps a list of points
 * @param  {Number} a  angle in degrees
 * @param  {Object} o  origin object
 * @return {Array<object>}    a list of rotated points
 */
function rotatePoints(ps, a, o) {
  return ps.map(function(p) {
    return {
      x: Math.cos(a) * ( p.x - o.x ) - Math.sin(a) * ( p.y - o.y ) + o.x,
      y: Math.sin(a) * ( p.x - o.x ) + Math.cos(a) * ( p.y - o.y ) + o.y
    };
  });
}