Add Heatmap layer to example

examples/export-map.js

@@ -1,8 +1,12 @@
 import GeoJSON from '../src/ol/format/GeoJSON.js';
 import Map from '../src/ol/Map.js';
 import View from '../src/ol/View.js';
+import {
+  Heatmap as HeatmapLayer,
+  Tile as TileLayer,
+  Vector as VectorLayer,
+} from '../src/ol/layer.js';
 import {OSM, Vector as VectorSource} from '../src/ol/source.js';
-import {Tile as TileLayer, Vector as VectorLayer} from '../src/ol/layer.js';
 
 const map = new Map({
   layers: [
@@ -16,6 +20,18 @@ const map = new Map({
       }),
       opacity: 0.5,
     }),
+    new HeatmapLayer({
+      source: new VectorSource({
+        url: 'data/geojson/world-cities.geojson',
+        format: new GeoJSON(),
+      }),
+      weight: function (feature) {
+        return feature.get('population') / 1e7;
+      },
+      radius: 15,
+      blur: 15,
+      opacity: 0.5,
+    }),
   ],
   target: 'map',
   view: new View({
@@ -32,17 +48,30 @@ document.getElementById('export-png').addEventListener('click', function () {
     mapCanvas.height = size[1];
     const mapContext = mapCanvas.getContext('2d');
     Array.prototype.forEach.call(
-      document.querySelectorAll('.ol-layer canvas'),
+      map.getViewport().querySelectorAll('.ol-layer canvas, canvas.ol-layer'),
       function (canvas) {
         if (canvas.width > 0) {
-          const opacity = canvas.parentNode.style.opacity;
+          const opacity =
+            canvas.parentNode.style.opacity || canvas.style.opacity;
           mapContext.globalAlpha = opacity === '' ? 1 : Number(opacity);
+          let matrix;
           const transform = canvas.style.transform;
-          // Get the transform parameters from the style's transform matrix
-          const matrix = transform
-            .match(/^matrix\(([^\(]*)\)$/)[1]
-            .split(',')
-            .map(Number);
+          if (transform) {
+            // Get the transform parameters from the style's transform matrix
+            matrix = transform
+              .match(/^matrix\(([^\(]*)\)$/)[1]
+              .split(',')
+              .map(Number);
+          } else {
+            matrix = [
+              parseFloat(canvas.style.width) / canvas.width,
+              0,
+              0,
+              parseFloat(canvas.style.height) / canvas.height,
+              0,
+              0,
+            ];
+          }
           // Apply the transform to the export map context
           CanvasRenderingContext2D.prototype.setTransform.apply(
             mapContext,