Thanks for the prompt reply.
I should have been more clear in my question I think. I am not using the Spine Plugin.
I want to load an atlas using Phaser's LoaderPlugin, like this:
this.load.atlas('mainmenu', 'images/MainMenu.png', 'images/MainMenu.json');
Here is a practical example from their web site: https://phaser.io/examples/v3/view/animation/texture-atlas-animation
I really like the texture packer from Spine, so I was hoping I could export the atlas in .json format, if possible.
