Add a stretchable image to the map

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.

<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Add a stretchable image to the map</title>
<script src="https://cdn.maptiler.com/maptiler-sdk-js/v3.0.1/maptiler-sdk.umd.min.js"></script>
<link href="https://cdn.maptiler.com/maptiler-sdk-js/v3.0.1/maptiler-sdk.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>
    maptilersdk.config.apiKey = 'YOUR_MAPTILER_API_KEY_HERE';
    const map = new maptilersdk.Map({
        container: 'map',
        style: maptilersdk.MapStyle.STREETS,
        zoom: 0.1
    });

    const images = {
        'popup': 'https://docs.maptiler.com/sdk-js/assets/popup.png',
        'popup-debug':
            'https://docs.maptiler.com/sdk-js/assets/popup_debug.png'
    };

    map.on('load', async () => {
        const debugPopup = await map.loadImage(images['popup-debug']);
        const popup = await map.loadImage(images['popup']);
        map.addImage('popup-debug', debugPopup.data, {
            // 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', popup.data, {
            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'
            }
        });
    });
</script>
</body>
</html>