Animate a line | TrackAsia GL JS Docs

Animate a line by updating a GeoJSON source on each frame.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Animate a line</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<script src="https://unpkg.com/trackasia-gl@1.0.5/dist/trackasia-gl.js"></script>
<link href="https://unpkg.com/trackasia-gl@1.0.5/dist/trackasia-gl.css" rel="stylesheet" />
<style>
	body { margin: 0; padding: 0; }
	#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<style>
button {
position: absolute;
margin: 20px;
}
 
#pause::after {
content: 'Pause';
}
 
#pause.pause::after {
content: 'Play';
}
</style>
<div id="map"></div>
<button id="pause"></button>
<script>
var map = new trackasiagl.Map({
container: 'map',
style: 'https://maps.track-asia.com/styles/v1/streets.json?key=public_key',
center: [0, 0],
zoom: 0.5
});
 
// Create a GeoJSON source with an empty lineString.
var geojson = {
'type': 'FeatureCollection',
'features': [
{
'type': 'Feature',
'geometry': {
'type': 'LineString',
'coordinates': [[0, 0]]
}
}
]
};
 
var speedFactor = 30; // number of frames per longitude degree
var animation; // to store and cancel the animation
var startTime = 0;
var progress = 0; // progress = timestamp - startTime
var resetTime = false; // indicator of whether time reset is needed for the animation
var pauseButton = document.getElementById('pause');
 
map.on('load', function () {
map.addSource('line', {
'type': 'geojson',
'data': geojson
});
 
// add the line which will be modified in the animation
map.addLayer({
'id': 'line-animation',
'type': 'line',
'source': 'line',
'layout': {
'line-cap': 'round',
'line-join': 'round'
},
'paint': {
'line-color': '#ed6498',
'line-width': 5,
'line-opacity': 0.8
}
});
 
startTime = performance.now();
 
animateLine();
 
// click the button to pause or play
pauseButton.addEventListener('click', function () {
pauseButton.classList.toggle('pause');
if (pauseButton.classList.contains('pause')) {
cancelAnimationFrame(animation);
} else {
resetTime = true;
animateLine();
}
});
 
// reset startTime and progress once the tab loses or gains focus
// requestAnimationFrame also pauses on hidden tabs by default
document.addEventListener('visibilitychange', function () {
resetTime = true;
});
 
// animated in a circle as a sine wave along the map.
function animateLine(timestamp) {
if (resetTime) {
// resume previous progress
startTime = performance.now() - progress;
resetTime = false;
} else {
progress = timestamp - startTime;
}
 
// restart if it finishes a loop
if (progress > speedFactor * 360) {
startTime = timestamp;
geojson.features[0].geometry.coordinates = [];
} else {
var x = progress / speedFactor;
// draw a sine wave with some math.
var y = Math.sin((x * Math.PI) / 90) * 40;
// append new coordinates to the lineString
geojson.features[0].geometry.coordinates.push([x, y]);
// then update the map
map.getSource('line').setData(geojson);
}
// Request the next frame of the animation.
animation = requestAnimationFrame(animateLine);
}
});
</script>
 
</body>
</html>