Merge pull request #9778 from ahocevar/faster-getsourcetiles

Return existing source tiles if at target resolution

src/ol/source/VectorTile.js

@@ -179,9 +179,7 @@ class VectorTile extends UrlTile {
    * @return {Array<import("../VectorTile").default>} Tile keys.
    */
   getSourceTiles(pixelRatio, projection, tile) {
-    const sourceTiles = [];
     const urlTileCoord = tile.wrappedTileCoord;
-    if (urlTileCoord) {
     const tileGrid = this.getTileGridForProjection(projection);
     const extent = tileGrid.getTileCoordExtent(urlTileCoord);
     const z = urlTileCoord[0];
@@ -196,6 +194,12 @@ class VectorTile extends UrlTile {
     const sourceZ = sourceTileGrid.getZForResolution(resolution, 1);
     const minZoom = sourceTileGrid.getMinZoom();
 
+    const previousSourceTiles = this.sourceTilesByTileKey_[getKey(tile.tileCoord)];
+    if (previousSourceTiles && previousSourceTiles.length > 0 && previousSourceTiles[0].tileCoord[0] === sourceZ) {
+      return previousSourceTiles;
+    }
+
+    const sourceTiles = [];
     let loadedZ = sourceZ + 1;
     let covered, empty;
     do {
@@ -265,7 +269,6 @@ class VectorTile extends UrlTile {
     if (covered || empty) {
       tile.hifi = sourceZ === loadedZ;
       tile.sourceZ = loadedZ;
-        const previousSourceTiles = this.sourceTilesByTileKey_[getKey(tile.tileCoord)];
       if (tile.getState() < TileState.LOADED) {
         tile.setState(empty ? TileState.EMPTY : TileState.LOADED);
       } else if (!previousSourceTiles || !equals(sourceTiles, previousSourceTiles)) {
@@ -273,7 +276,6 @@ class VectorTile extends UrlTile {
         this.addSourceTiles(tile, sourceTiles);
       }
     }
-    }
     return sourceTiles;
   }