Firebase plugin is not working with OSD and dynamic tile sources

[darkmich]

Steps to replicate: Set up an OpenSeadragon instance using a dynamic tile source, initialize the Annotorious OSD plugin. Try to load the Firebase plugin.

Error: When annotations are saved, they're always saved as the base URL plus "undefined".

This seems to be due to Firebase using the URL from OSDAnnotationLayer.js (lines 66+67):

      const src = this.viewer.world.getItemAt(0).source['@id'] || 
        new URL(this.viewer.world.getItemAt(0).source.url, document.baseURI).href;

In our OSD implementation, this.viewer.world.getItemAt(0).source.url is undefined. This can be worked around by setting it prior to calling Firebase - that has to be done in TileDoneHandler to make sure that source is defined, as it's only defined when OSD actually puts something in the canvas:

var tileDrawnHandler = function(event) {
  viewer.removeHandler('tile-drawn', tileDrawnHandler);
viewer.world.getItemAt(0).source.url = <URL>

I suspect this is because our OSD tile source isn't a file - we're loading tiles from S3-storage as we need them.

    var viewer = OpenSeadragon({
        id: "openseadragon1",
        prefixUrl: "https://cdnjs.cloudflare.com/ajax/libs/openseadragon/2.4.2/images/",
		navigatorAutoFade:  false,
        showNavigator:  true,
        zoomInButton:   "zoomIn",
   		zoomOutButton:  "zoomOut",
   	 	homeButton:     "home",
	    fullPageButton: "fullscreen",
        gestureSettingsTouch: {
        	pinchRotate: true
    	},
        success: function(event) {
        	imageDone = true;
        },
    tileSources:   {height: 243848,
width: 106312,
tileSize: 2048,

        overlap: 1,
		getTileUrl: function( level, x, y ){return "<URL>"+ level + "/" + x + "_" + y + ".jpg";
        }
    }
});

I suspect OSD isn't setting source.url because there's no one URL for the source - we get the tiles as we go along.