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Hack for easing full rotations and idea for adding to Spine
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It's known that Spine can't do a normal 360° and so it's become standard to do 3x 120° key frames. This is problematic when attempting a tween ease, as most people defer to copy/pasting the rotation and moving the key frames closer rather than painstakingly figuring out the actual rotations per frame. It's not ideal when looking for accuracy and can easily fall apart visually. After some tinkering, I came up with a great hack that solves this and am offering a solution on implementation into spine for any devs reading this.
Essentially the trick is to create a standard 0-120 degree rotation on a bone, then copy that bone and parent it inside the first one. Repeat this as needed, as every 3 produces a full 360° rotation. Now select all those key frames and apply the same ease as needed. This is extremely useful for creating effects like a wheel spinning up slow to fast to slow again.
My one issue with this is it's very cluttery, as something like a 1080° spin uses 9 nested bones. Since true rotations with easable control is a highly requested feature, I've thought of how this working hack can be implemented into an update:
Create a new bone sub type (we'll call it multi-bone). Basically it functions exactly like a bone in the skeleton except whatever is done to it can have its effects "multiplied" (EX: multiply [3] times). In essence all it will do is duplicate itself X amount of times in a series of parent bones under the hood, but in the skeleton UI it will be one easy to manage element.
Interesting approach! I'd like to try it out some time. The only problem is the number of bones you need to achieve it.
Here's one that used the "pasting the keyframes together and putting them closer" approach: Animating a spin? Daily Reward Wheel Question.
I'd say it's hardly noticeable once you look at the final animation, but if one is looking for a fine approach, yours is definitely interesting, thanks for sharing! I'll also share your suggestion with the team
It'd be really cool and useful if there was an overall "graph" tween thing we could click on for each bone, and one for the overall animation playback. This would control the overall playback speed for each animations bone and the overall animation. Not sure if I'm wording that right sorry, but it'd make things like speeding up wheels very easy, and lot's of other interesting things!! Probably quite mathematically complicated though :rofl:
@valorware - Can you make video tutorial about this method plz!
Well, I tried it out and made a small project.
It's interesting for sure, in regards to easing, but ultimately I think I still prefer the good old method of the 3 keyframes.
You basically still have 3 keyframes this way, but instead of having them on a single bone, you split them across multiple bones.
It has the advantage of making the easing of curves easier, but the con of still needing 3 keyframes for each bone when you decide to still do a complete rotation.
It was fun 
so thanks for sharing!
mfedorov ：@[已注销] - Can you make video tutorial about this method plz!
I don't have a method sorry, it was an idea proposal to make this sort of thing easier so you could do it on 1 bone AND have 1 curve for all the keyframes inside it (and give a massive potential to many other uses)!
Oh, i understand the idea now. Pretty handy hack. Thank you!