Tests for and adjustments to unpack alignment handling

test/rendering/cases/webgl-data-tile-3-band/main.js

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+import DataTile from '../../../../src/ol/source/DataTile.js';
+import Map from '../../../../src/ol/Map.js';
+import TileLayer from '../../../../src/ol/layer/WebGLTile.js';
+import View from '../../../../src/ol/View.js';
+
+const size = [81, 99];
+
+const canvas = document.createElement('canvas');
+canvas.width = size[0];
+canvas.height = size[1];
+
+const context = canvas.getContext('2d');
+context.strokeStyle = 'white';
+context.textAlign = 'center';
+const lineHeight = 16;
+context.font = `${lineHeight}px sans-serif`;
+
+new Map({
+  target: 'map',
+  layers: [
+    new TileLayer({
+      source: new DataTile({
+        loader: function (z, x, y) {
+          const halfWidth = size[0] / 2;
+          const halfHeight = size[1] / 2;
+          context.fillStyle = '#00AAFF';
+          context.fillRect(0, 0, size[0], size[1]);
+          context.fillStyle = 'white';
+          context.fillText(`z: ${z}`, halfWidth, halfHeight - lineHeight);
+          context.fillText(`x: ${x}`, halfWidth, halfHeight);
+          context.fillText(`y: ${y}`, halfWidth, halfHeight + lineHeight);
+          context.strokeRect(0, 0, size[0], size[1]);
+          const data = context.getImageData(0, 0, size[0], size[1]).data;
+
+          const bandCount = 3;
+          const result = data.filter((_, index) => index % 4 < bandCount);
+          return Promise.resolve(result);
+        },
+        tileSize: size,
+      }),
+    }),
+  ],
+  view: new View({
+    center: [0, 0],
+    zoom: 4,
+  }),
+});
+
+render({tolerance: 0.03});