Support multiple sources for layers

examples/cog-pyramid.html

@@ -4,9 +4,8 @@ title: GeoTIFF tile pyramid
 shortdesc: Rendering a COG tile pyramid as layer group.
 docs: >
   Data from a Cloud Optimized GeoTIFF (COG) tile pyramid can be rendered as a set of layers.  In this
-  example, a pyramid of 3-band GeoTIFFs is used to render RGB data. For each tile of the pyramid, a
-  separate layer is created on demand. The lowest resolution layer serves as preview while higher resolutions are
-  loading.
+  example, a pyramid of 3-band GeoTIFFs is used to render RGB data. The `ol/source.sourcesFromTileGrid`
+  helper function creates sources from this pyramid on demand.
 tags: "cog, tilepyramid, stac"
 ---
 <div id="map" class="map"></div>

examples/cog-pyramid.js

@@ -1,16 +1,16 @@
 import GeoTIFF from '../src/ol/source/GeoTIFF.js';
-import LayerGroup from '../src/ol/layer/Group.js';
 import Map from '../src/ol/Map.js';
 import TileGrid from '../src/ol/tilegrid/TileGrid.js';
 import View from '../src/ol/View.js';
 import WebGLTileLayer from '../src/ol/layer/WebGLTile.js';
-import {getIntersection} from '../src/ol/extent.js';
+import {createXYZ} from '../src/ol/tilegrid.js';
+import {sourcesFromTileGrid} from '../src/ol/source.js';
 
 // Metadata from https://s2downloads.eox.at/demo/EOxCloudless/2019/rgb/2019_EOxCloudless_rgb.json
 
 // Tile grid of the GeoTIFF pyramid layout
 const tileGrid = new TileGrid({
-  origin: [-180, 90],
+  extent: [-180, -90, 180, 90],
   resolutions: [0.703125, 0.3515625, 0.17578125, 8.7890625e-2, 4.39453125e-2],
   tileSizes: [
     [512, 256],
@@ -21,30 +21,25 @@ const tileGrid = new TileGrid({
   ],
 });
 
-const pyramid = new LayerGroup();
-const layerForUrl = {};
-const zs = tileGrid.getResolutions().length;
-
-function useLayer(z, x, y) {
-  const url = `https://s2downloads.eox.at/demo/EOxCloudless/2019/rgb/${z}/${y}/${x}.tif`;
-  if (!(url in layerForUrl)) {
-    pyramid.getLayers().push(
-      new WebGLTileLayer({
-        minZoom: z,
-        maxZoom: z === 0 || z === zs - 1 ? undefined : z + 1,
-        extent: tileGrid.getTileCoordExtent([z, x, y]),
-        source: new GeoTIFF({
-          sources: [
-            {
-              url: url,
-            },
-          ],
+const pyramid = new WebGLTileLayer({
+  sources: sourcesFromTileGrid(
+    tileGrid,
+    ([z, x, y]) =>
+      new GeoTIFF({
+        tileGrid: createXYZ({
+          extent: tileGrid.getTileCoordExtent([z, x, y]),
+          minZoom: z,
+          maxZoom:
+            z === tileGrid.getResolutions().length - 1 ? undefined : z + 1,
         }),
+        sources: [
+          {
+            url: `https://s2downloads.eox.at/demo/EOxCloudless/2019/rgb/${z}/${y}/${x}.tif`,
+          },
+        ],
       })
-    );
-    layerForUrl[url] = true;
-  }
-}
+  ),
+});
 
 const map = new Map({
   target: 'map',
@@ -56,16 +51,3 @@ const map = new Map({
     showFullExtent: true,
   }),
 });
-
-// Add overview layer
-useLayer(0, 0, 0);
-
-// Add layer for specific extent on demand
-map.on('moveend', () => {
-  const view = map.getView();
-  tileGrid.forEachTileCoord(
-    getIntersection([-180, -90, 180, 90], view.calculateExtent()),
-    tileGrid.getZForResolution(view.getResolution()),
-    ([z, x, y]) => useLayer(z, x, y)
-  );
-});

src/ol/layer/Base.js

@@ -163,7 +163,6 @@ class BaseLayer extends BaseObject {
       });
     const zIndex = this.getZIndex();
     state.opacity = clamp(Math.round(this.getOpacity() * 100) / 100, 0, 1);
-    state.sourceState = this.getSourceState();
     state.visible = this.getVisible();
     state.extent = this.getExtent();
     state.zIndex = zIndex === undefined && !state.managed ? Infinity : zIndex;

src/ol/layer/Layer.js

@@ -57,7 +57,7 @@ import {listen, unlistenByKey} from '../events.js';
  * @typedef {Object} State
  * @property {import("./Layer.js").default} layer Layer.
  * @property {number} opacity Opacity, the value is rounded to two digits to appear after the decimal point.
- * @property {import("../source/State.js").default} sourceState SourceState.
+ * @property {import("../source/Source.js").default|undefined} source Source being rendered (only for multi-source layers).
  * @property {boolean} visible Visible.
  * @property {boolean} managed Managed.
  * @property {import("../extent.js").Extent} [extent] Extent.
@@ -196,6 +196,13 @@ class Layer extends BaseLayer {
     return /** @type {SourceType} */ (this.get(LayerProperty.SOURCE)) || null;
   }
 
+  /**
+   * @return {SourceType} The source being rendered.
+   */
+  getRenderSource() {
+    return this.getSource();
+  }
+
   /**
    * @return {import("../source/State.js").default} Source state.
    */

src/ol/layer/WebGLTile.js

@@ -3,6 +3,7 @@
  */
 import BaseTileLayer from './BaseTile.js';
 import LayerProperty from '../layer/Property.js';
+import SourceState from '../source/State.js';
 import WebGLTileLayerRenderer, {
   Attributes,
   Uniforms,
@@ -64,6 +65,11 @@ import {assign} from '../obj.js';
  * @property {number} [preload=0] Preload. Load low-resolution tiles up to `preload` levels. `0`
  * means no preloading.
  * @property {SourceType} [source] Source for this layer.
+ * @property {Array<SourceType>|function(import("../extent.js").Extent, number):Array<SourceType>} [sources] Array
+ * of sources for this layer. Takes precedence over `source`. Can either be an array of sources, or a function that
+ * expects an extent and a resolution (in view projection units per pixel) and returns an array of sources. See
+ * {@link module:ol/source.sourcesFromTileGrid} for a helper function to generate sources that are organized in a
+ * pyramid following the same pattern as a tile grid.
  * @property {import("../PluggableMap.js").default} [map] Sets the layer as overlay on a map. The map will not manage
  * this layer in its layers collection, and the layer will be rendered on top. This is useful for
  * temporary layers. The standard way to add a layer to a map and have it managed by the map is to
@@ -291,6 +297,18 @@ class WebGLTileLayer extends BaseTileLayer {
 
     super(options);
 
+    /**
+     * @type {Array<SourceType>|function(import("../extent.js").Extent, number):Array<SourceType>}
+     * @private
+     */
+    this.sources_ = options.sources;
+
+    /**
+     * @type {number}
+     * @private
+     */
+    this.renderedResolution_ = NaN;
+
     /**
      * @type {Style}
      * @private
@@ -312,6 +330,41 @@ class WebGLTileLayer extends BaseTileLayer {
     this.addChangeListener(LayerProperty.SOURCE, this.handleSourceUpdate_);
   }
 
+  /**
+   * Gets the sources for this layer, for a given extent and resolution.
+   * @param {import("../extent.js").Extent} extent Extent.
+   * @param {number} resolution Resolution.
+   * @return {Array<SourceType>} Sources.
+   */
+  getSources(extent, resolution) {
+    const source = this.getSource();
+    return this.sources_
+      ? typeof this.sources_ === 'function'
+        ? this.sources_(extent, resolution)
+        : this.sources_
+      : source
+      ? [source]
+      : [];
+  }
+
+  /**
+   * @return {SourceType} The source being rendered.
+   */
+  getRenderSource() {
+    return (
+      /** @type {SourceType} */ (this.getLayerState().source) ||
+      this.getSource()
+    );
+  }
+
+  /**
+   * @return {import("../source/State.js").default} Source state.
+   */
+  getSourceState() {
+    const source = this.getRenderSource();
+    return source ? source.getState() : SourceState.UNDEFINED;
+  }
+
   /**
    * @private
    */
@@ -340,6 +393,66 @@ class WebGLTileLayer extends BaseTileLayer {
     });
   }
 
+  /**
+   * @param {import("../PluggableMap").FrameState} frameState Frame state.
+   * @param {Array<SourceType>} sources Sources.
+   * @return {HTMLElement} Canvas.
+   */
+  renderSources(frameState, sources) {
+    const layerRenderer = this.getRenderer();
+    let canvas;
+    for (let i = 0, ii = sources.length; i < ii; ++i) {
+      this.getLayerState().source = sources[i];
+      if (layerRenderer.prepareFrame(frameState)) {
+        canvas = layerRenderer.renderFrame(frameState);
+      }
+    }
+    return canvas;
+  }
+
+  /**
+   * @param {?import("../PluggableMap.js").FrameState} frameState Frame state.
+   * @param {HTMLElement} target Target which the renderer may (but need not) use
+   * for rendering its content.
+   * @return {HTMLElement} The rendered element.
+   */
+  render(frameState, target) {
+    const viewState = frameState.viewState;
+    const sources = this.getSources(frameState.extent, viewState.resolution);
+    let ready = true;
+    for (let i = 0, ii = sources.length; i < ii; ++i) {
+      const source = sources[i];
+      const sourceState = source.getState();
+      if (sourceState == SourceState.LOADING) {
+        const onChange = () => {
+          if (source.getState() == SourceState.READY) {
+            source.removeEventListener('change', onChange);
+            this.changed();
+          }
+        };
+        source.addEventListener('change', onChange);
+      }
+      ready = ready && sourceState == SourceState.READY;
+    }
+    const canvas = this.renderSources(frameState, sources);
+    if (this.getRenderer().renderComplete && ready) {
+      // Fully rendered, done.
+      this.renderedResolution_ = viewState.resolution;
+      return canvas;
+    }
+    // Render sources from previously fully rendered frames
+    if (this.renderedResolution_ > 0.5 * viewState.resolution) {
+      const altSources = this.getSources(
+        frameState.extent,
+        this.renderedResolution_
+      ).filter((source) => !sources.includes(source));
+      if (altSources.length > 0) {
+        return this.renderSources(frameState, altSources);
+      }
+    }
+    return canvas;
+  }
+
   /**
    * Update the layer style.  The `updateStyleVariables` function is a more efficient
    * way to update layer rendering.  In cases where the whole style needs to be updated,

src/ol/renderer/Composite.js

@@ -110,15 +110,17 @@ class CompositeMapRenderer extends MapRenderer {
     for (let i = 0, ii = layerStatesArray.length; i < ii; ++i) {
       const layerState = layerStatesArray[i];
       frameState.layerIndex = i;
+
+      const layer = layerState.layer;
+      const sourceState = layer.getSourceState();
       if (
         !inView(layerState, viewState) ||
-        (layerState.sourceState != SourceState.READY &&
-          layerState.sourceState != SourceState.UNDEFINED)
+        (sourceState != SourceState.READY &&
+          sourceState != SourceState.UNDEFINED)
       ) {
         continue;
       }
 
-      const layer = layerState.layer;
       const element = layer.render(frameState, previousElement);
       if (!element) {
         continue;

src/ol/renderer/webgl/Layer.js

@@ -161,7 +161,7 @@ class WebGLLayerRenderer extends LayerRenderer {
    * @return {boolean} Layer is ready to be rendered.
    */
   prepareFrame(frameState) {
-    if (this.getLayer().getSource()) {
+    if (this.getLayer().getRenderSource()) {
       let incrementGroup = true;
       let groupNumber = -1;
       let className;

src/ol/renderer/webgl/TileLayer.js

@@ -20,7 +20,6 @@ import {
 } from '../../vec/mat4.js';
 import {
   createOrUpdate as createTileCoord,
-  getKeyZXY,
   getKey as getTileCoordKey,
 } from '../../tilecoord.js';
 import {fromUserExtent} from '../../proj.js';
@@ -98,7 +97,7 @@ function getRenderExtent(frameState, extent) {
     );
   }
   const source =
-    /** {import("../../source/Tile.js").default} */ layerState.layer.getSource();
+    /** {import("../../source/Tile.js").default} */ layerState.layer.getRenderSource();
   if (!source.getWrapX()) {
     const gridExtent = source
       .getTileGridForProjection(frameState.viewState.projection)
@@ -110,6 +109,10 @@ function getRenderExtent(frameState, extent) {
   return extent;
 }
 
+function getCacheKey(source, tileCoord) {
+  return `${source.getKey()},${getTileCoordKey(tileCoord)}`;
+}
+
 /**
  * @typedef {Object} Options
  * @property {string} vertexShader Vertex shader source.
@@ -140,6 +143,12 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
       uniforms: options.uniforms,
     });
 
+    /**
+     * The last call to `renderFrame` was completed with all tiles loaded
+     * @type {boolean}
+     */
+    this.renderComplete = false;
+
     /**
      * This transform converts tile i, j coordinates to screen coordinates.
      * @type {import("../../transform.js").Transform}
@@ -273,7 +282,7 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
    */
   prepareFrameInternal(frameState) {
     const layer = this.getLayer();
-    const source = layer.getSource();
+    const source = layer.getRenderSource();
     if (!source) {
       return false;
     }
@@ -293,7 +302,7 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
   enqueueTiles(frameState, extent, z, tileTexturesByZ) {
     const viewState = frameState.viewState;
     const tileLayer = this.getLayer();
-    const tileSource = tileLayer.getSource();
+    const tileSource = tileLayer.getRenderSource();
     const tileGrid = tileSource.getTileGridForProjection(viewState.projection);
     const tileTextureCache = this.tileTextureCache_;
     const tileRange = tileGrid.getTileRangeForExtentAndZ(
@@ -314,7 +323,7 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
     for (let x = tileRange.minX; x <= tileRange.maxX; ++x) {
       for (let y = tileRange.minY; y <= tileRange.maxY; ++y) {
         const tileCoord = createTileCoord(z, x, y, this.tempTileCoord_);
-        const tileCoordKey = getTileCoordKey(tileCoord);
+        const cacheKey = getCacheKey(tileSource, tileCoord);
 
         /**
          * @type {TileTexture}
@@ -326,8 +335,8 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
          */
         let tile;
 
-        if (tileTextureCache.containsKey(tileCoordKey)) {
-          tileTexture = tileTextureCache.get(tileCoordKey);
+        if (tileTextureCache.containsKey(cacheKey)) {
+          tileTexture = tileTextureCache.get(cacheKey);
           tile = tileTexture.tile;
         }
         if (!tileTexture || tileTexture.tile.key !== tileSource.getKey()) {
@@ -340,7 +349,7 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
           );
           if (!tileTexture) {
             tileTexture = new TileTexture(tile, tileGrid, this.helper);
-            tileTextureCache.set(tileCoordKey, tileTexture);
+            tileTextureCache.set(cacheKey, tileTexture);
           } else {
             if (this.isDrawableTile_(tile)) {
               tileTexture.setTile(tile);
@@ -379,12 +388,13 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
    * @return {HTMLElement} The rendered element.
    */
   renderFrame(frameState) {
+    this.renderComplete = true;
     const gl = this.helper.getGL();
     this.preRender(gl, frameState);
 
     const viewState = frameState.viewState;
     const tileLayer = this.getLayer();
-    const tileSource = tileLayer.getSource();
+    const tileSource = tileLayer.getRenderSource();
     const tileGrid = tileSource.getTileGridForProjection(viewState.projection);
     const extent = getRenderExtent(frameState, frameState.extent);
     const z = tileGrid.getZForResolution(
@@ -438,6 +448,7 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
         const tileCoordKey = getTileCoordKey(tileCoord);
         alphaLookup[tileCoordKey] = alpha;
       }
+      this.renderComplete = false;
 
       // first look for child tiles (at z + 1)
       const coveredByChildren = this.findAltTiles_(
@@ -635,9 +646,10 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
 
     let covered = true;
     const tileTextureCache = this.tileTextureCache_;
+    const source = this.getLayer().getRenderSource();
     for (let x = tileRange.minX; x <= tileRange.maxX; ++x) {
       for (let y = tileRange.minY; y <= tileRange.maxY; ++y) {
-        const cacheKey = getKeyZXY(altZ, x, y);
+        const cacheKey = getCacheKey(source, [altZ, x, y]);
         let loaded = false;
         if (tileTextureCache.containsKey(cacheKey)) {
           const tileTexture = tileTextureCache.get(cacheKey);

src/ol/source.js

@@ -2,6 +2,9 @@
  * @module ol/source
  */
 
+import LRUCache from './structs/LRUCache.js';
+import {getIntersection} from './extent.js';
+
 export {default as BingMaps} from './source/BingMaps.js';
 export {default as CartoDB} from './source/CartoDB.js';
 export {default as Cluster} from './source/Cluster.js';
@@ -31,3 +34,35 @@ export {default as VectorTile} from './source/VectorTile.js';
 export {default as WMTS} from './source/WMTS.js';
 export {default as XYZ} from './source/XYZ.js';
 export {default as Zoomify} from './source/Zoomify.js';
+
+/**
+ * Creates a sources function from a tile grid. This function can be used as value for the
+ * `sources` property of the {@link module:ol/layer/Layer~Layer} subclasses that support it.
+ * @param {import("./tilegrid/TileGrid.js").default} tileGrid Tile grid.
+ * @param {function(import("./tilecoord.js").TileCoord): import("./source/Source.js").default} factory Source factory.
+ * This function takes a {@link module:ol/tilecoord~TileCoord} as argument and is expected to return a
+ * {@link module:ol/source/Source~Source}.
+ * @return {function(import("./extent.js").Extent, number): Array<import("./source/Source.js").default>} Sources function.
+ * @api
+ */
+export function sourcesFromTileGrid(tileGrid, factory) {
+  const sourceCache = new LRUCache(32);
+  const tileGridExtent = tileGrid.getExtent();
+  return function (extent, resolution) {
+    sourceCache.expireCache();
+    if (tileGridExtent) {
+      extent = getIntersection(tileGridExtent, extent);
+    }
+    const z = tileGrid.getZForResolution(resolution);
+    const wantedSources = [];
+    tileGrid.forEachTileCoord(extent, z, (tileCoord) => {
+      const key = tileCoord.toString();
+      if (!sourceCache.containsKey(key)) {
+        const source = factory(tileCoord);
+        sourceCache.set(key, source);
+      }
+      wantedSources.push(sourceCache.get(key));
+    });
+    return wantedSources;
+  };
+}

src/ol/structs/LRUCache.js

@@ -66,6 +66,16 @@ class LRUCache {
     return this.highWaterMark > 0 && this.getCount() > this.highWaterMark;
   }
 
+  /**
+   * Expire the cache.
+   * @param {!Object<string, boolean>} [keep] Keys to keep. To be implemented by subclasses.
+   */
+  expireCache(keep) {
+    while (this.canExpireCache()) {
+      this.pop();
+    }
+  }
+
   /**
    * FIXME empty description for jsdoc
    */

test/browser/spec/ol/layer/Group.test.js

@@ -44,7 +44,6 @@ describe('ol/layer/Group', function () {
         opacity: 1,
         visible: true,
         managed: true,
-        sourceState: 'ready',
         extent: undefined,
         zIndex: undefined,
         maxResolution: Infinity,
@@ -161,7 +160,6 @@ describe('ol/layer/Group', function () {
         opacity: 0.5,
         visible: false,
         managed: true,
-        sourceState: 'ready',
         extent: undefined,
         zIndex: 10,
         maxResolution: 500,
@@ -203,7 +201,6 @@ describe('ol/layer/Group', function () {
         opacity: 0.5,
         visible: false,
         managed: true,
-        sourceState: 'ready',
         extent: groupExtent,
         zIndex: undefined,
         maxResolution: 500,
@@ -399,7 +396,6 @@ describe('ol/layer/Group', function () {
         opacity: 0.3,
         visible: false,
         managed: true,
-        sourceState: 'ready',
         extent: groupExtent,
         zIndex: 10,
         maxResolution: 500,
@@ -417,7 +413,6 @@ describe('ol/layer/Group', function () {
         opacity: 0,
         visible: false,
         managed: true,
-        sourceState: 'ready',
         extent: undefined,
         zIndex: undefined,
         maxResolution: Infinity,
@@ -433,7 +428,6 @@ describe('ol/layer/Group', function () {
         opacity: 1,
         visible: true,
         managed: true,
-        sourceState: 'ready',
         extent: undefined,
         zIndex: undefined,
         maxResolution: Infinity,
@@ -599,7 +593,6 @@ describe('ol/layer/Group', function () {
         opacity: 0.25,
         visible: false,
         managed: true,
-        sourceState: 'ready',
         extent: undefined,
         zIndex: undefined,
         maxResolution: 150,

test/browser/spec/ol/layer/Layer.test.js

@@ -56,7 +56,6 @@ describe('ol/layer/Layer', function () {
         opacity: 1,
         visible: true,
         managed: true,
-        sourceState: 'ready',
         extent: undefined,
         zIndex: undefined,
         maxResolution: Infinity,
@@ -95,7 +94,6 @@ describe('ol/layer/Layer', function () {
         opacity: 0.5,
         visible: false,
         managed: true,
-        sourceState: 'ready',
         extent: undefined,
         zIndex: 10,
         maxResolution: 500,
@@ -430,7 +428,6 @@ describe('ol/layer/Layer', function () {
         opacity: 0.33,
         visible: false,
         managed: true,
-        sourceState: 'ready',
         extent: undefined,
         zIndex: 10,
         maxResolution: 500,

test/browser/spec/ol/layer/WebGLTile.test.js

@@ -373,4 +373,37 @@ describe('ol/layer/WebGLTile', function () {
       done();
     });
   });
+
+  it('handles multiple sources correctly', () => {
+    const source = layer.getSource();
+    expect(layer.getRenderSource()).to.be(source);
+    layer.sources_ = (extent, resolution) => {
+      return [
+        {
+          getState: () => 'ready',
+          extent,
+          resolution,
+          id: 'source1',
+        },
+        {
+          getState: () => 'ready',
+          extent,
+          resolution,
+          id: 'source2',
+        },
+      ];
+    };
+    const sourceIds = [];
+    layer.getRenderer().prepareFrame = (frameState) => {
+      const renderedSource = layer.getRenderSource();
+      expect(renderedSource.extent).to.eql([0, 0, 100, 100]);
+      expect(renderedSource.resolution).to.be(1);
+      sourceIds.push(renderedSource.id);
+    };
+    layer.render({
+      extent: [0, 0, 100, 100],
+      viewState: {resolution: 1},
+    });
+    expect(sourceIds).to.eql(['source1', 'source2']);
+  });
 });

test/browser/spec/ol/source.test.js

@@ -0,0 +1,41 @@
+import TileGrid from '../../../../src/ol/tilegrid/TileGrid.js';
+import XYZ from '../../../../src/ol/source/XYZ.js';
+import {createXYZ} from '../../../../src/ol/tilegrid.js';
+import {get} from '../../../../src/ol/proj.js';
+import {sourcesFromTileGrid} from '../../../../src/ol/source.js';
+
+describe('ol/source', function () {
+  describe('sourcesFromTileGrid()', function () {
+    it('returns a function that returns the correct source', function () {
+      const resolutions = createXYZ({maxZoom: 1}).getResolutions();
+      const tileGrid = new TileGrid({
+        extent: get('EPSG:3857').getExtent(),
+        resolutions: [resolutions[1]],
+        tileSizes: [[256, 512]],
+      });
+      const factory = function (tileCoord) {
+        return new XYZ({
+          url: tileCoord.join('-') + '/{z}/{x}/{y}.png',
+          tileGrid: new TileGrid({
+            resolutions,
+            minZoom: tileCoord[0],
+            maxZoom: tileCoord[0] + 1,
+            extent: tileGrid.getTileCoordExtent(tileCoord),
+            origin: [-20037508.342789244, 20037508.342789244],
+          }),
+        });
+      };
+      const getSources = sourcesFromTileGrid(tileGrid, factory);
+      expect(getSources(tileGrid.getExtent(), resolutions[1]).length).to.be(2);
+      expect(
+        getSources(
+          [-10000, -10000, -5000, 10000],
+          resolutions[1]
+        )[0].getUrls()[0]
+      ).to.be('0-0-0/{z}/{x}/{y}.png');
+      expect(
+        getSources([5000, -10000, 10000, 10000], resolutions[1])[0].getUrls()[0]
+      ).to.be('0-1-0/{z}/{x}/{y}.png');
+    });
+  });
+});

test/rendering/cases/webgl-tile-multisource/main.js

@@ -0,0 +1,58 @@
+import Map from '../../../../src/ol/Map.js';
+import TileGrid from '../../../../src/ol/tilegrid/TileGrid.js';
+import TileLayer from '../../../../src/ol/layer/WebGLTile.js';
+import View from '../../../../src/ol/View.js';
+import XYZ from '../../../../src/ol/source/XYZ.js';
+import {createXYZ} from '../../../../src/ol/tilegrid.js';
+import {get} from '../../../../src/ol/proj.js';
+import {sourcesFromTileGrid} from '../../../../src/ol/source.js';
+
+const resolutions = createXYZ({maxZoom: 1}).getResolutions();
+const tilePyramid = new TileGrid({
+  extent: get('EPSG:3857').getExtent(),
+  resolutions: [resolutions[1]],
+  tileSizes: [[256, 512]],
+});
+
+new Map({
+  target: 'map',
+  layers: [
+    new TileLayer({
+      sources: sourcesFromTileGrid(tilePyramid, (tileCoord) => {
+        let source;
+        switch (tileCoord.toString()) {
+          case '0,1,0':
+            source = new XYZ({
+              url: '/data/tiles/osm/{z}/{x}/{y}.png',
+              tileGrid: new TileGrid({
+                resolutions,
+                minZoom: tileCoord[0],
+                maxZoom: tileCoord[0] + 1,
+                extent: tilePyramid.getTileCoordExtent(tileCoord),
+                origin: [-20037508.342789244, 20037508.342789244],
+              }),
+            });
+            break;
+          default:
+            source = new XYZ({
+              url: '/data/tiles/satellite/{z}/{x}/{y}.jpg',
+              tileGrid: new TileGrid({
+                resolutions,
+                minZoom: tileCoord[0],
+                maxZoom: tileCoord[0] + 1,
+                extent: tilePyramid.getTileCoordExtent(tileCoord),
+                origin: [-20037508.342789244, 20037508.342789244],
+              }),
+            });
+        }
+        return source;
+      }),
+    }),
+  ],
+  view: new View({
+    center: [0, 0],
+    zoom: 1,
+  }),
+});
+
+render();