touch - jquery apply momentum of inertia on drag -


i write little script drag div container. works touch , mouse events.

i have difficulties write momentum script in order have container moving after touchend. know how calculate momentum don't know right way implement it...

here script : 

var divtodrag = $('.container'); var divondrag = $(document);  var dragging = false; var swipe = false; var scrolly = false; var threshold = {x:30, y:10}; var swipeleft = false; var swiperight = false; var swipeup = false; var swipedown = false; var threshx = false; var threshy = false;  var maxspeed = 5;  function prefix() {   styles = window.getcomputedstyle(document.documentelement, ''),     pre = (array.prototype.slice       .call(styles)       .join('')        .match(/-(moz|webkit|ms)-/) || (styles.olink === '' && ['', 'o'])     )[1],     dom = ('webkit|moz|ms|o').match(new regexp('(' + pre + ')', 'i'))[1]; } prefix();  function pointereventxy(e) {       out = {x:0, y:0};       if(e.type == 'touchstart' || e.type == 'touchmove' || e.type == 'touchend'){         touch = e.originalevent.touches[0] || e.originalevent.changedtouches[0];         out.x = touch.pagex;         out.y = touch.pagey;       } else if (e.type == 'mousedown' || e.type == 'mouseup' || e.type == 'mousemove') {         out.x = e.pagex;         out.y = e.pagey;       }       return out; };  divondrag.on('mousedown touchstart', function(event){     dragging = true;     divtodrag.stop();     pointereventxy(event);     startcoordsx = prevcoordsx = out.x;     startcoordsy = prevcoordsy = out.y;     divcoordsx = divtodrag.position().left;     divcoordsy = divtodrag.position().top;     initialcoordsx = startcoordsx - divcoordsx;     initialcoordsy = startcoordsy - divcoordsy;     divtodrag.data("mouseevents",[event]); })  divondrag.on('mousemove touchmove', function(event){         if (dragging == true) {         pointereventxy(event);         currentcoordsx = out.x;         currentcoordsy = out.y;         xthreshold = math.abs(currentcoordsx - startcoordsx)         ythreshold = math.abs(currentcoordsy - startcoordsy)          var mouseevents = divtodrag.data( "mouseevents" );           if ((event.timestamp - mouseevents[ mouseevents.length - 1 ].timestamp ) > 40){             mouseevents.push(event);             if (mouseevents.length > 2){                 mouseevents.shift();             }         }          if(xthreshold > threshold.x && ythreshold < threshold.y && scrolly == false || swipe == true ) {             event.preventdefault();             swipe = true;             dragdirection();             x = currentcoordsx - initialcoordsx - threshx;             y = currentcoordsy - initialcoordsy - threshy;             divtodrag.attr('style', '-'+pre+'-transition: 0s ease-in !important; -'+pre+'-transform: translate3d('+x+'px, 0px, 0px)');         } else if (xthreshold < threshold.x && ythreshold > threshold.y) {             scrolly = true;         }     } })  divondrag.on('mouseup touchend',  function(event){     dragging = false;     scrolly = false;     swipe = false;     swipeleft = false;     swiperight = false;     swipeup = false;     swipedown = false;     momentum(); })  function dragdirection() {      if (prevcoordsx < currentcoordsx) {         swiperight = true;           threshx = threshold.x;     } else if (prevcoordsx > currentcoordsx) {         swipeleft = true;         threshx = -threshold.x;     }      if (prevcoordsy < currentcoordsy) {         swipedown = true;            threshy = threshold.y;     } else if (prevcoordsy > currentcoordsy) {         swipeup = true;          threshy = -threshold.y;     }     if (swiperight == true && swipeleft == true || swipeup == true && swipedown == true) {         threshx = 0;             threshy = 0;         prevcoordsx = currentcoordsx - initialcoordsx;         prevcoordsy = currentcoordsy - initialcoordsy;     }     prevcoordsx = currentcoordsx;     prevcoordsy = currentcoordsy; }  function momentum() {      var lastevent = divtodrag.data( "mouseevents" ).shift();     if (!lastevent){         return;     }     var deltax = (event.pagex - lastevent.pagex);     var deltay = (event.pagey - lastevent.pagey);     var deltams = math.max((event.timestamp - lastevent.timestamp),1);     var speedx = math.max(math.min( (deltax / deltams), maxspeed ),-maxspeed);     var speedy = math.max(math.min( (deltay / deltams), maxspeed ),-maxspeed);       var laststeptime = new date();            divtodrag.animate(         {textindent: 0},         {duration: (math.max(math.abs( speedx ), math.abs( speedy )) * 3000),         step: function( currentstep ){                 speedx *= (currentstep / 100);                 speedy *= (currentstep / 100);                 var = new date();                 var stepduration = (now.gettime() - laststeptime.gettime());                 laststeptime = now;                 var position = divtodrag.position();                 var newleft = (position.left + (speedx * stepduration));                 var newtop = (position.top + (speedy * stepduration));                   console.log(newleft)                 divtodrag.css({transform: 'translatex('+newleft+'px)'});                 }         }     ); }

and fiddle : http://jsfiddle.net/v5jmu/2/

update

http://jsfiddle.net/rdyqb/12/

i made new fiddle seems work better matjazek answer

i recommend solve problem different aproach, if insist in using method, should job done:

http://jsfiddle.net/rdyqb/

you can set drag coeficient with

var drag=0.95; // drag coeficient

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