src/js/hammer.js
function getScale(start, end) {
    return getDistance(end[0], end[1], PROPS_CLIENT_XY) / getDistance(start[0], start[1], PROPS_CLIENT_XY);
}
function getScale(start, end) {
    return getDistance(end[0], end[1], PROPS_CLIENT_XY) / getDistance(start[0], start[1], PROPS_CLIENT_XY);
}
function getScale ( start , end ) { return getDistance ( end [ 0 ] , end [ 1 ] , PROPS_CLIENT_XY ) / getDistance ( start [ 0 ] , start [ 1 ] , PROPS_CLIENT_XY ) ; }
calculate the scale factor between two pointersets
no scale is 1, and goes down to 0 when pinched together, and bigger when pinched out
@param {Array} start array of pointers
@param {Array} end array of pointers
@return {Number} scale
calculate the scale factor between two pointersets no scale is 1 and goes down to 0 when pinched together and bigger when pinched out