Cannot use imageTile.setImage() in the tileLoadFunction about openlayers HOT 5 OPEN

Please note that ImageTile#setImage() is not an API method. We could change that, but first I'd be curious to hear more about your use case. Internally, that method is used to set an already loaded image as a tile's image.

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Thanks @ahocevar for the quick answer.

I am using a multilevel tile cache for improving performance, and I am "sometime" able to precalculate bitmaps in advance: bitmap = await createImageBitmap(blob);. I am also thinking about creating a worker thread for bitmap rendering.

So I looked at OL code and found that nice setImage() function which was doing exactly what I wanted ;)

Doing it the "official way":

let imageUrl = URL.createObjectURL(blob); 
imageTile.getImage().src = imageUrl;

is convoluted, slow, and uses a lot of CPU.

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You are getting the error because setImage() takes an image or canvas element, ImageBitmap is not supported and would need to be included in typedefs.

However I think the suggested change is valid as where setImage() is currently used (as in TileDebug) the code is needlessly setting a listener on a canvas. Also the statement order in setImage should be the same as that in handleImageError_ so any listener is removed before updating this.image_.

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A sensible change would be a bit more involved. Currently, ol/ImageTile already creates a HTMLImageElement at construction time, which is not needed for the use case described here. ol/source/Image and ol/source/DataTile have a configurable loader, and this is what we should be aiming for. See #14258.

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Thanks @ahocevar for hinting me to #14258. It looks like #14262 is really the right direction to follow in the long term.

Meanwhile, in an attempt to squeeze now the last drop of power from limited devices, I have subclassed XYZ, and overloaded getTileInternal() to intercept tile requests and stuff new tiles from my cache in OL's .

This is definitely not "casher", but works like a charm as long as I use my forked version of OL:

  getTileInternal(z, x, y, pixelRatio, projection) {
    const tileCoordKey = getKeyZXY(z, x, y);
    const olKey = this.getKey();
    const myKey = makeKey2(provider.id, x, y, z);
    if (this.tileCache.containsKey(tileCoordKey)) {
      // Tile already in OL cache
      const olTile = this.tileCache.get(tileCoordKey);
      if (olTile.key == olKey) {
        return XYZ.prototype.getTileInternal.call(this, z, x, y, pixelRatio, projection);
      }
    }
    const rr = tcPrefetch.read(myKey);
    if (rr === null) {
      // Tile not available in prefetch cache
      return XYZ.prototype.getTileInternal.call(this, z, x, y, pixelRatio, projection);
    }
    // Create new tile and stuff it in OL cache
    const tile = this.createTile_(z, x, y, pixelRatio, projection, olKey);
    // Plagiarized from ImageTile#setImage()
    tile.image_ = rr.value.bitmap;
    tile.state = TileState.LOADED;
    this.tileCache.set(tileCoordKey, tile);
    this.changed();
    return tile;
  }
}

Thanks again

Michel

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