index.js
function getRotation(start, end) {
  return getAngle(end[1], end[0], PROPS_CLIENT_XY) - getAngle(start[1], start[0], PROPS_CLIENT_XY);
}
function getRotation(start, end) {
  return getAngle(end[1], end[0], PROPS_CLIENT_XY) - getAngle(start[1], start[0], PROPS_CLIENT_XY);
}
function getRotation ( start , end ) { return getAngle ( end [ 1 ] , end [ 0 ] , PROPS_CLIENT_XY ) - getAngle ( start [ 1 ] , start [ 0 ] , PROPS_CLIENT_XY ) ; }
calculate the rotation degrees between two pointersets
@param {Array} start array of pointers
@param {Array} end array of pointers
@return {Number} rotation
calculate the rotation degrees between two pointersets