Add render test for immediate render with pixel ratio 2

test/rendering/cases/immediate-pixel-ratio/main.js

@@ -0,0 +1,76 @@
+import VectorLayer from '../../../../src/ol/layer/Vector.js';
+import VectorSource from '../../../../src/ol/source/Vector.js';
+import {Feature, Map, View} from '../../../../src/ol/index.js';
+import {Fill, Icon, Stroke, Style, Text} from '../../../../src/ol/style.js';
+import {LineString, MultiPoint, Point} from '../../../../src/ol/geom.js';
+import {getVectorContext} from '../../../../src/ol/render.js';
+
+const coordinates = [
+  [50, -200, 0],
+  [200, -200, 0],
+  [100, -50, 0],
+];
+const img = new Image();
+img.src =
+  'data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxMCIgaGVpZ2h0PSIxMCIgdmlld0JveD0iMCAwIDIwIDIwIiBzdHlsZT0iYmFja2dyb3VuZC1jb2xvcjogZ3JlZW47Ij48cGF0aCBkPSJtIDEwIDEwIDEwdiAtMTBoIiAvPjwvc3ZnPg==';
+const point = new MultiPoint(coordinates);
+const pointStyle = new Style({
+  image: new Icon({
+    img: img,
+    size: [10, 10],
+    imgSize: [10, 10],
+  }),
+});
+const line = new LineString(coordinates);
+const lineStyle = new Style({
+  stroke: new Stroke({
+    color: 'red',
+    width: 40,
+    lineCap: 'square',
+    lineJoin: 'round',
+    lineDash: [30, 100],
+    lineDashOffset: 5,
+  }),
+  text: new Text({
+    text: '--- T e s t ___',
+    placement: 'point',
+    fill: new Fill({
+      color: 'green',
+    }),
+    font: '50px Ubuntu',
+    stroke: new Stroke({
+      color: 'blue',
+      width: 10,
+      lineCap: 'butt',
+      lineDash: [10, 5],
+      lineDashOffset: 4,
+    }),
+  }),
+});
+
+const vector = new VectorLayer({
+  source: new VectorSource({
+    features: [new Feature(new Point([-20, -20]))],
+  }),
+});
+
+vector.on('postrender', function (evt) {
+  const context = getVectorContext(evt);
+  context.setStyle(lineStyle);
+  context.drawGeometry(line);
+
+  context.setStyle(pointStyle);
+  context.drawGeometry(point);
+});
+
+new Map({
+  target: 'map',
+  layers: [vector],
+  view: new View({
+    center: [256 / 2, -256 / 2],
+    resolution: 1,
+    devicePixelRatio: 2,
+  }),
+});
+
+render();