Layer clipping example
Layer clipping example
import 'ol/ol.css';
import Map from 'ol/Map';
import OSM from 'ol/source/OSM';
import TileLayer from 'ol/layer/Tile';
import View from 'ol/View';
const osm = new TileLayer({
source: new OSM(),
});
const map = new Map({
layers: [osm],
target: 'map',
view: new View({
center: [0, 0],
zoom: 2,
}),
});
osm.on('prerender', function (event) {
const ctx = event.context;
// calculate the pixel ratio and rotation of the canvas
const matrix = event.inversePixelTransform;
const canvasPixelRatio = Math.sqrt(
matrix[0] * matrix[0] + matrix[1] * matrix[1]
);
const canvasRotation = -Math.atan2(matrix[1], matrix[0]);
ctx.save();
// center the canvas and remove rotation to position clipping
ctx.translate(ctx.canvas.width / 2, ctx.canvas.height / 2);
ctx.rotate(-canvasRotation);
ctx.scale(3 * canvasPixelRatio, 3 * canvasPixelRatio);
ctx.translate(-75, -80);
ctx.beginPath();
ctx.moveTo(75, 40);
ctx.bezierCurveTo(75, 37, 70, 25, 50, 25);
ctx.bezierCurveTo(20, 25, 20, 62.5, 20, 62.5);
ctx.bezierCurveTo(20, 80, 40, 102, 75, 120);
ctx.bezierCurveTo(110, 102, 130, 80, 130, 62.5);
ctx.bezierCurveTo(130, 62.5, 130, 25, 100, 25);
ctx.bezierCurveTo(85, 25, 75, 37, 75, 40);
ctx.clip();
ctx.translate(75, 80);
ctx.scale(1 / 3 / canvasPixelRatio, 1 / 3 / canvasPixelRatio);
// reapply canvas rotation and position
ctx.rotate(canvasRotation);
ctx.translate(-ctx.canvas.width / 2, -ctx.canvas.height / 2);
});
osm.on('postrender', function (event) {
const ctx = event.context;
ctx.restore();
});
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Layer Clipping</title>
<!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
<script src="https://unpkg.com/elm-pep"></script>
<!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
<script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,URL,TextDecoder,Number.isInteger"></script>
<style>
.map {
width: 100%;
height:400px;
}
#map {
background: transparent;
}
</style>
</head>
<body>
<div id="map" class="map"></div>
<script src="main.js"></script>
</body>
</html>
{
"name": "layer-clipping",
"dependencies": {
"ol": "6.6.1"
},
"devDependencies": {
"parcel": "^2.0.0-beta.1"
},
"scripts": {
"start": "parcel index.html",
"build": "parcel build --public-url . index.html"
}
}