Index bigger than number of layers when loading in multilayer IIIF images

[BeebBenjamin]

We are loading in manifests that contain images with multiple layers, the index value for example is 4 (so 5 layers). I have noticed that OSD throws an error when the index value is bigger than or equal to the number of layers when loading these in. For us, this is naturally because the layers are loading in asynchronously, and the count is sometimes initially smaller when this function is called, sometimes we do not get the error on a refresh. I have a feeling that something is not quite right.

[pearcetm]

How are you actually loading these into the viewer once the information is available asynchronously? With viewer.addTiledImage()? Or some other way?

[BeebBenjamin]

I will have to look at Mirador viewer and get back to you.

[BeebBenjamin]

@pearcetm Mirador uses viewer.addTiledImage() in it's OpenSeadragonViewer component.

[BeebBenjamin]

Here is the section:

viewer.addTiledImage({
        error: event => reject(event),
        fitBounds: new OpenSeadragon.Rect(
          ...canvasWorld.contentResourceToWorldCoordinates(contentResource),
        ),
        index: canvasWorld.layerIndexOfImageResource(contentResource),
        opacity: canvasWorld.layerOpacityOfImageResource(contentResource),
        success: event => resolve(event),
        tileSource,
      });

[BeebBenjamin]

Here it is in context: https://github.com/ProjectMirador/mirador/blob/5cb692ed31480c1e130f4a8715726688cb35796d/src/components/OpenSeadragonViewer.js#L229

[pearcetm]

I can't tell just from the code what is going on. Is there a demo page that shows the behavior you're describing? What is the error message you're seeing?

OSD can add tiled images with index undefined, and doesn't have a problem if an index is greater than viewer.world.getItemCount()+1, and even handles negative numbers as the index.

You might try using the debugger to see what value is being returned from canvasWorld.layerIndexOfImageResource(contentResource) and other mirador-specific calls.

[iangilman]

I have noticed that OSD throws an error when the index value is bigger than or equal to the number of layers when loading these in.

What index value?

[BeebBenjamin]

Sure here: https://iiif.bodleian.ox.ac.uk/iiif/mirador/?iiif-content=https://iiif.bodleian.ox.ac.uk/iiif/manifest/1fc3f35d-bbb5-4524-8fbe-a5bcb5468be2.json

[BeebBenjamin]

Error is:

Uncaught (in promise) Error: Index bigger than number of layers.
    at e.World.setItemIndex (mirador-with-plugins.js:2:1421440)
    at mirador-with-plugins.js:2:565942
    at Array.forEach (<anonymous>)
    at a.value (mirador-with-plugins.js:2:565813)
    at mirador-with-plugins.js:2:564695

[pearcetm]

Ok, so the error is being thrown from World.setImageIndex(). It looks like there's a mismatch between what mirador thinks the "layer index" is (or can be) versus the number of images that have actually been loaded into viewer at the time. This is because mirador (or your application) knows about all the images that will eventually be loaded, while OSD only knows about those that have already been added to the viewer. In a viewer with only one image, it doesn't make sense to tell it that the image should be at index = 4 in the array - so OSD throws an error.

There are probably a number of ways this could be handled, but keeping track within mirador/application code of which images have actually been added to the viewer, and what index they are within the viewer.world, is probably the best approach.

[BeebBenjamin]

There is a bug is Mirador 3 that might related to this issue: ProjectMirador/mirador#3585