Triggering a Lottie animation onScroll - fullpage.js

Question

im currently building a website using fullpage js and lottie animations. Now im trying to trigger an animation when the user scrolls to the section with the animation. Here is what i tried:
(please note that im very new to js)
$(document).ready(function($) {'use strict';
$('#fullpage').fullpage({
sectionsColor: ['white', '#004E8A', 'white','#004E8A', 'white', '#004E8A',
'white','#004E8A', 'white'],
anchors:['startseite','pers_vermittler','team','konzept','rechner','mod_portfolio','sicherheit','absatz'],
onLeave: function(index, nextIndex, direction) {
if( index == 3 && direction == 'down' ) {
lottie.play('k2an');
}
(at the end of the body section ->)
<script>
var params = {
container: document.getElementById('k2an'),
renderer: 'svg',
loop: true,
autoplay: false,
path: 'k2an.json',
};
anim = lottie.loadAnimation(params);

Answer 1

You should be using fullPage.js callbacks to fire your JS animations.
See the example:
$('#fullpage').fullpage({
anchors: ['firstPage', 'secondPage', 'thirdPage', 'fourthPage', 'lastPage'],
afterLoad: function(anchorLink, index){
var loadedSection = $(this);
//using index
if(index == 3){
alert("Section 3 ended loading");
}
//using anchorLink
if(anchorLink == 'secondSlide'){
alert("Section 2 ended loading");
}
}
});
Feel free to also check my video tutorial on how to create animations using fullPage.js state classes.

Answer 2

Right now im using this approach on a couple production sites. It plays the animation as the user scrolls.
I basically check how much of the animation objects box is visible in the viewport, calculate the total length of the animation (in frames) and then project the percentage to a frame where i gotoAndStop().
var anim = <YOUR LOTTIE ANIMATION OBJECT>
// play around with these
var speed = 1; // speed of animation
var scrollOffset = 0; // start animation sooner / later
function scrollHandler() {
if (!anim.isLoaded) return;
p = percentageSeen(e) / 100 - (scrollOffset || 0);
if (p <= 0 || p >= 1) return
var length = anim.totalFrames / anim.frameModifier;
var pos = length * p * (speed || 1);
anim.goToAndStop(pos);
}
$(window).on('scroll', scrollHandler);
/**
* returns percentage of scrolling element through viewport
* 0% until element-middle is at bottom of viewport
* 100% if element-middle is at top of viewport
*
* #param id
* #returns {number}
*/
function percentageSeen(idOrElement) {
var $element;
if (typeof idOrElement === 'object') {
$element = idOrElement;
} else {
$element = $('#' + id);
if (!$element[0]) return 0;
}
var $win = $(window), viewportHeight = $(window).height(),
scrollTop = $win.scrollTop(),
elementOffsetTop = $element.offset().top,
elementHeight = $element.height();
if (elementOffsetTop > (scrollTop + viewportHeight)) {
return 0;
} else if ((elementOffsetTop + elementHeight) < scrollTop) {
return 100;
} else {
var distance = (scrollTop + viewportHeight) - elementOffsetTop - (elementHeight / 2);
if (distance < 0) return 0;
var percentage = distance / (viewportHeight / 100);
if (percentage > 100) return 100;
return percentage;
}
}
If you want to only start the animation and let it run (independently of further user-scrolling-behaviour), just use the jquery inview plugin, disable autoplay on your animation and trigger the play() once like this:
$(".animation-container").one("inview", function() {
anim.play()
});