Add a stretchable image to the map | TrackAsia GL JS Docs

Use a stretchable image as a background for text. Stretchable images allow some parts of the image to stretch while keeping other parts, such as corners, at a constant size. Set the layout property 'icon-text-fit': 'both' to use the image as background for the text.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Add a stretchable image to the map</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>
<div id="map"></div>
 
<script>
var map = new trackasiagl.Map({
container: 'map',
style: 'https://static.track-asia.com/demotiles/styles/osm-bright-gl-style/style.json?key=public_key',
zoom: 0.1
});
 
var images = {
'popup': 'https://docs.track-asia.com/assets/popup.png',
'popup-debug': 'https://docs.track-asia.com/assets/popup_debug.png'
};
 
loadImages(images, function (loadedImages) {
map.on('load', function () {
map.addImage('popup-debug', loadedImages['popup-debug'], {
// The two (blue) columns of pixels that can be stretched horizontally:
//   - the pixels between x: 25 and x: 55 can be stretched
//   - the pixels between x: 85 and x: 115 can be stretched.
stretchX: [
[25, 55],
[85, 115]
],
// The one (red) row of pixels that can be stretched vertically:
//   - the pixels between y: 25 and y: 100 can be stretched
stretchY: [[25, 100]],
// This part of the image that can contain text ([x1, y1, x2, y2]):
content: [25, 25, 115, 100],
// This is a high-dpi image:
pixelRatio: 2
});
map.addImage('popup', loadedImages['popup'], {
stretchX: [
[25, 55],
[85, 115]
],
stretchY: [[25, 100]],
content: [25, 25, 115, 100],
pixelRatio: 2
});
 
map.addSource('points', {
'type': 'geojson',
'data': {
'type': 'FeatureCollection',
'features': [
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [40, -30]
},
'properties': {
'image-name': 'popup-debug',
'name': 'Line 1\nLine 2\nLine 3'
}
},
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [40, 30]
},
'properties': {
'image-name': 'popup',
'name': 'Line 1\nLine 2\nLine 3'
}
},
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [-40, -30]
},
'properties': {
'image-name': 'popup-debug',
'name': 'One longer line'
}
},
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [-40, 30]
},
'properties': {
'image-name': 'popup',
'name': 'One longer line'
}
}
]
}
});
map.addLayer({
'id': 'points',
'type': 'symbol',
'source': 'points',
'layout': {
'text-field': ['get', 'name'],
'icon-text-fit': 'both',
'icon-image': ['get', 'image-name'],
'icon-overlap': 'always',
'text-overlap': 'always'
}
});
 
// the original, unstretched image for comparison
map.addSource('original', {
'type': 'geojson',
'data': {
'type': 'FeatureCollection',
'features': [
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [0, -70]
}
}
]
}
});
map.addLayer({
'id': 'original',
'type': 'symbol',
'source': 'original',
'layout': {
'text-field': 'unstretched image',
'icon-image': 'popup-debug',
'icon-overlap': 'always',
'text-overlap': 'always'
}
});
});
});
 
function loadImages(urls, callback) {
var results = {};
for (var name in urls) {
map.loadImage(urls[name], makeCallback(name));
}
 
function makeCallback(name) {
return function (err, image) {
results[name] = err ? null : image;
 
// if all images are loaded, call the callback
if (Object.keys(results).length === Object.keys(urls).length) {
callback(results);
}
};
}
}
</script>
 
</body>
</html>