Adding easing on requestAnimationFrame

问题:

I need to reproduce the same effect as here: http://www.chanel.com/fr_FR/mode/haute-couture.html = a swipe effect on mouse move event.

I just need some help on the animation part.

    function frame() {
      $('.images-gallery').css({
        'transform': 'translateX('+ -mouseXPerc +'%)'
      });
      requestAnimationFrame(frame);
    }

    requestAnimationFrame(frame);
    $(document).on('mousemove',function(e){
      mouseXPerc = e.pageX/containerWidth*100;

    });

Here's what I've done so far. It works as supposed, but as you can imagine, it's pretty raw, I need some easing in that. How can I edit my frame() function to get something smoother ?

Edit : I can't use CSS transition / animation as I change the value on requestAnimationFrame (each 1/30 sec).

回答1:

I think I've found an answer for you. It's based on this library

First, I would just grab a function from that site

function inOutQuad(n){
    n *= 2;
    if (n < 1) return 0.5 * n * n;
    return - 0.5 * (--n * (n - 2) - 1);
};

Then, I would use a modified form of the example code, something like this

function startAnimation(domEl){
    var stop = false;

    // animating x (margin-left) from 20 to 300, for example
    var startx = 20;
    var destx = 300;
    var duration = 1000;
    var start = null;
    var end = null;

    function startAnim(timeStamp) {
        start = timeStamp;
        end = start + duration;
        draw(timeStamp);
    }

    function draw(now) {
        if (stop) return;
        if (now - start >= duration) stop = true;
        var p = (now - start) / duration;
        val = inOutQuad(p);
        var x = startx + (destx - startx) * val;
        $(domEl).css('margin-left', `${x}px`);
        requestAnimationFrame(draw);
    }

    requestAnimationFrame(startAnim);
}

I might change how 'stop' is calculated, I might write something to ensure that it ends on destx, etc, but that's the basic format

Showing it in this jsfiddle

I'm actually kinda proud of this one. I've been wanting to figure this out for a while. Glad I had a reason to.

回答2:

You can create your own ease function and use it inside your frame function:

var ease = function() {
    var x = 0;
    return function(x_new) {
        x = (x_new+x)*.5;
        return x;
    }
}();

function frame() {
  $('.images-gallery').css({
    'transform': 'translateX('+ -ease(mouseXPerc) +'%)'
  });
  requestAnimationFrame(frame);
}

requestAnimationFrame(frame);
$(document).on('mousemove',function(e){
  mouseXPerc = e.pageX/containerWidth*100;

});