examples/touch/hammer.js
function getVelocity(delta_time, delta_x, delta_y) {
    return {
      x: Math.abs(delta_x / delta_time) || 0,
      y: Math.abs(delta_y / delta_time) || 0
    };
  }
function getVelocity(delta_time, delta_x, delta_y) {
    return {
      x: Math.abs(delta_x / delta_time) || 0,
      y: Math.abs(delta_y / delta_time) || 0
    };
  }
function getVelocity ( delta_time , delta_x , delta_y ) { return { x : Math . abs ( delta_x / delta_time ) || 0 , y : Math . abs ( delta_y / delta_time ) || 0 } ; }
calculate the velocity between two points
@param   {Number}    delta_time
@param   {Number}    delta_x
@param   {Number}    delta_y
@returns {Object}    velocity
calculate the velocity between two points