Export SVG slice coordinates in Spine JSON (or alternative)

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I'm building a GUI application that renders its widgets from SVGs, and I've found that I can export slice coordinates using the Spine JSON batch builder. However, the slice coordinates and sizes are only exported for binary image formats. I would like them for SVGs, too!

 

I appreciate that scalable vector graphics don't necessarily have defined sizes, nor does Spine support SVGs, but it would make my workflow much quicker if I could access the positions of my slices in either the Spine JSON or some other text file (preferably JSON). This would allow me to script my application build, positioning my widgets automatically, every time I export all slices again.