@Nate So, I played around with physics and I noticed something that I remembered reading about on the forum (link to post below), physics loop while in the editor if deterministic physics are disabled. However, when exporting the loop is broken because the physics pose resets on the first frame rather than carrying through the motion. Presumably, the export uses deterministic physics. So, If its possible to implement the ability to export using non-deterministic physics, looping can be achieved if the simulation is pre-run a couple times before the export happens. Maybe it would be possible to advanced the physics, letting it loop a couple times. Then advance the physics, draw the skeleton (and other stuff that's needed) to a render target / buffer and save it and repeat until the animation is finished. If its not easy to add to the editor I think I should be able to do this using the runtime. Although, having it built into the editor would be best.
Also, See this forum post where the same behavior is described. It also seems like this post describes the same behavior.
This video is a screen capture of the editor, with non-deterministic physics running at 120 fps, which I trimmed so that video matches the length of the animation and the animation was pre-run. If you right click on the video and select loop and watch it a couple times you can tell that the physics are looping.
Here is the animation exported to a gif, as you can see it is no longer looping. If you enable deterministic physics in the editor you can see that it also does not loop in a similar / same way as the .gif.
I feel like it should also be possible to loop with deterministic physics as well. Here is a gif where I copied the animation and pasted it on the end of the animation. Also, I keyed the rotation on the start and end frames before copy pasting. I then exported it by limiting the export range to the duplicated animation and enabling include last frame in the export.
Also, this isn't related to looping but I noticed when I enable deterministic physics the end bone has a weird rotation on the start frame.
Also, sorry this is also not related but I was wondering when the spine-c and spice-c++ runtimes would be updated for 4.2. Not expecting a exact time frame I was just wondering how far down in the list they are compared to other runtimes.