Animate a line
Animate a line by updating a GeoJSON source on each frame.
<!DOCTYPE html>
<html lang="en">
<head>
<title>Animate a line</title>
<meta property="og:description" content="Animate a line by updating a GeoJSON source on each frame." />
<meta charset='utf-8'>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel='stylesheet' href='https://unpkg.com/maplibre-gl@4.7.1/dist/maplibre-gl.css' />
<script src='https://unpkg.com/maplibre-gl@4.7.1/dist/maplibre-gl.js'></script>
<style>
body { margin: 0; padding: 0; }
html, body, #map { height: 100%; }
</style>
</head>
<body>
<style>
button {
position: absolute;
top: 0;
margin: 20px;
}
#pause::after {
content: 'Pause';
}
#pause.pause::after {
content: 'Play';
}
</style>
<div id="map"></div>
<button id="pause"></button>
<script>
const map = new maplibregl.Map({
container: 'map',
style:
'https://api.maptiler.com/maps/streets/style.json?key=get_your_own_OpIi9ZULNHzrESv6T2vL',
center: [0, 0],
zoom: 0.5
});
// Create a GeoJSON source with an empty lineString.
const geojson = {
'type': 'FeatureCollection',
'features': [
{
'type': 'Feature',
'geometry': {
'type': 'LineString',
'coordinates': [[0, 0]]
}
}
]
};
const speedFactor = 30; // number of frames per longitude degree
let animation; // to store and cancel the animation
let startTime = 0;
let progress = 0; // progress = timestamp - startTime
let resetTime = false; // indicator of whether time reset is needed for the animation
const pauseButton = document.getElementById('pause');
map.on('load', () => {
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', () => {
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', () => {
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 {
const x = progress / speedFactor;
// draw a sine wave with some math.
const 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>