An OpenSeadragon plugin that adds SVG overlay capability.
Compatible only with the new "Collections" branch of OpenSeadragon.
To use, include the openseadragon-svg-overlay.js file after openseadragon.js on your web page.
To add SVG overlay capability to your OpenSeadragon Viewer, call svgOverlay() on it. This will return the SVG g element that you should add all of your SVG elements to. As the user zooms and pans, the g element will transform to match. Add your elements according to the OpenSeadragon Viewport coordinate system.
Note that if you want to be able to receive events on any of the SVG elements you add, you'll need to set their pointer-events property accordingly. Using a value of 'fill' seems to work nicely.
If your viewer changes size, you'll need to resize the SVG overlay by calling svgOverlay('resize') on your Viewer.
See demo.html for an example of it in use. You can see it in action at http://openseadragon.github.io/svg-overlay/demo.html.