Add rendering test for image style opacity

rendering/cases/icon-opacity/main.js

@@ -0,0 +1,47 @@
+import Map from '../../../src/ol/Map.js';
+import View from '../../../src/ol/View.js';
+import {Vector as VectorLayer, Tile as TileLayer} from '../../../src/ol/layer.js';
+import {Vector as VectorSource, XYZ} from '../../../src/ol/source.js';
+import Point from '../../../src/ol/geom/Point.js';
+import Feature from '../../../src/ol/Feature.js';
+import {fromLonLat} from '../../../src/ol/proj.js';
+import {Style, Icon} from '../../../src/ol/style.js';
+
+const center = fromLonLat([8.6, 50.1]);
+
+new Map({
+  layers: [
+    new TileLayer({
+      source: new XYZ({
+        url: '/data/tiles/satellite/{z}/{x}/{y}.jpg'
+      })
+    }),
+    new VectorLayer({
+      style: function() {
+        return new Style({
+          image: new Icon({
+            opacity: 0.5,
+            src: '/data/icon.png',
+            anchor: [0.5, 46],
+            anchorXUnits: 'fraction',
+            anchorYUnits: 'pixels'
+          })
+        });
+      },
+      source: new VectorSource({
+        features: [
+          new Feature(
+            new Point(center)
+          )
+        ]
+      })
+    })
+  ],
+  target: 'map',
+  view: new View({
+    center: center,
+    zoom: 3
+  })
+});
+
+render();