Help with IK

Yimec · 2024年2月15日

I have an animation to do where I work with a somewhat cartoonish carnivorous plant. This plant, in Unity, will have a fixed point (the roots) and a movable part (the head) (imagine the plants from Super Mario). The idea is for it to move its head towards the target to try to eat it. This plant has a "neck" of a certain length, but it's flexible, like a "rope" that limits it.

My idea is to move the head with IK, positioning the target bone at the target, but the limitation of two bones feels insufficient, as this "neck" has more intermediate bones. Therefore, I'm not sure how to approach this animation.

Any suggestions? Is there any tool in Spine for what I'm trying to achieve?

If more information is needed from my side, please let me know, and I'll provide it.

Thank you in advance!

Erika · 2024年2月15日

It sounds like path constraints could be perfect for the job! Especially since a path constraint can also be weighted to follow a target bone as well.
You can find an example of such a setup in the Vine project in the Editor of Spine.
Related there's also the leg of stretchyman here:
http://esotericsoftware.com/spine-examples-stretchyman

I hope this helps!

Yimec · 2024年2月15日

Hi @Erika !
So, please let me know if I've understood the workflow correctly.

Currently, my rig resembles the image on the right:

There are numerous bones along the neck.

Am I supposed to replace these with a path? Additionally, is it necessary for this path to have only three anchors? And then, should I link this path to two IK bones? Is my understanding accurate?

Looking forward to your guidance on these matters, all these rather "convoluted" procedures are beyond my understanding of the tool, and I appreciate any advice you can provide.

Thank you again, Erika!

EDIT:
This is my plant's "neck" so far, in case it helps you helping me!:

Misaki · 2024年2月15日

Yimec

Am I supposed to replace these with a path?

No, you do not need to replace the existing bones, but rather constrain them to a path attachment using a path constraint. When you use a path constraint to constrain bones to a path, the bones will move with the path when you deform the path attachment.
Path attachments have "knots", which are vertices on the path, and "handles", which are vertices that control the curve of the path between knots. Path attachments can be attached to any bone to give weight to knots and handles. Thus, while a mesh attachment is bound to a large number of bones, the path attachment that constrains those bones can be deformed with a much smaller number of bones, resulting in flexible control of the mesh attachment with a smaller number of bones.

And one of the benefits of having fewer bones is the availability of IK constraints. By binding a path attachment to two bones and setting IK constraints on those two bones, you can use IK constraints while achieving smooth curvilinear deformation of the mesh.

I think it will be easy to understand if you actually open the Spine project of Stretchyman and check it.
Note that the bones constrained by path attachments are hidden by default in the project. This may make the rig look very simple, even though it actually uses many bones: