I just finished up a portrait I'm using to learn Spine. I have almost zero experience animating, and it's been a journey. Animation curves are still mostly gibberish to me. I actually restarted everything a few times, so it's nice to be done. Anyway, I was inspired by the portraits I've seen created with Live2D and thought I'd do the same in Spine. Problem is, there's not much Spine-specific information for this kind of stuff. Most of the tutorials are for full-body rigs. I ended up studying how characters are constructed and rigged in 3D packages.

Here's the final result. Note that I did some post-processing work in After Effects:
https://streamable.com/qrdi18

A look my bone setup:

Her face mesh. I based it on some low-poly images I found on Google Image Search. I also browsed Sketchfab for characters with a similar style and used them to further refine the mesh:

Here's how I did the faux 3D effect. First, I created a profile and some numbered lines. I take these numbers into Spine and input them into the "Weight" field for a bone I've named "controller_head_front". For example, in Photoshop there's a line almost exactly at the tip of her nose. The line is numbered "22", and that's what I input into Spine. This works great for any vertices directly on the center of her face. Other vertices require a bit of guesswork, but with such a solid base to work with things are made much easier. I should also mention that I rigged the mouth, eyes, etc. before adding the faux 3D effect. Doing it the other way around is unadvised, as weighting the face will also adjust the weights for your painstakingly done faux 3D:

So, there you go. I'm generally happy with the results, and think I've avoided the "swimmy" look Live2D portraits tend to have.

Nate wrote

Wow, very nice! I like how you used the lines in the side view to help setting weights. It's also interesting how you made a box with bones, at the top of the first GIF. We'd love to add built in support for "joystick" style controls similar to that.

A joystick system would be super useful, especially if you could place them anywhere on the canvas. Oh, and custom boundaries, too. Round, square, etc.

Nate wrote

The rig is very finely detailed! That can be great when it's needed, though people should also consider less detail when it's not needed. Often I see very complex rigs which look great when zoomed in, but I have to think in many cases they won't be used at such extreme zoom levels. Yours very well may be of course, like the video, and the detail allows for subtle expressions so it doesn't look like a doll.

Thanks for sharing!

I had a lot of trouble figuring out how detailed the mesh needed to be and ended up settling on PS2-era detail levels (or around that, anyway). I definitely could trim some vertices here and there, but due to how I shaded the character I needed to be careful and not be too conservative with the vertex count. If she was flat shaded I could've used more shortcuts, but she's not, so...

Nate wrote

I wonder, what do you mean that Live2D tends to look "swimmy"?

I've noticed with some virtual Youtubers that their facial features don't look fully attached to their head. Whenever they look around their eyes/nose/whatever slide around unnaturally. I haven't used Live2D, but I assume it has to do with how you rig characters in it. Rather than using one or two bones for faux 3D like in Spine, artists have to drag around vertices manually, and that leaves more room for error. Admittedly, I've seen good results, so it's mostly down to artist skill and how well they understand perspective.