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agentronin

Animating a Wrist Rotation

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Posted (edited)

I need to turn a wrist so that when, for the example, the arm is hanging down the hand's palm is facing to the rear, it faces forward after rotation. I find this unnaturally deforms the mesh at the wrist. It looks a lot like the hand is being twisted off.

This video is about a solution:

Unfortunately this solution requires the forearm bone to be divided into three bones. Since this for an animation in SL I do not have the option to put three bones in the forearm. Is there an SL animation compatible way to solve this?

Edited by agentronin
Grammar correction

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Posted (edited)

You could do it by setting drivers on the collision volume bone, so that the local axis running through the length of the arm rotates 50% of the wrist's rotation. Such collision volume bone shold be weighted accordingly, and for a custom character it may work well. Another solution, that runs slower on playback though, is to drive the same collision volume bone through a scripted expression.

Edited by OptimoMaximo
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Would this collision volume bone be something already in a standard SL Bento Avatar? Or would this have to be added? I need this animation to work in SL on my Slink Physique body with its Vista Animations Bento hands. The avatar I have in Blender was created by Avastar with all the standard SL Bento bones, and shaped by an XML shape slider file from that Slink Physique body.

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You could do it by setting drivers on the collision volume bone, so that the local axis running through the length of the arm rotates 50% of the wrist's rotation

Does "through the length of the arm" mean the entire length of the arm from wrist to shoulder?

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13 hours ago, agentronin said:

Would this collision volume bone be something already in a standard SL Bento Avatar?

Collision Volume bones are standard even before Bento additional bones came out, they are used for shape sliders and, as the name implies, determine the volume of the worn mesh. They can be animated using .anim animation format. You need a compliant avatar to begin with, since their location is established in the avatar already. The default avatar from Avastar works.

13 hours ago, agentronin said:

I need this animation to work in SL on my Slink Physique body with its Vista Animations Bento hands

And how exactly do you think to make 2 standalone animations to work together this way? One animation can't be aware of another animation rotations, it's something you "program" (drivers or scripted expression) in your own animation to work together as you wish. You must make your own animations involving wrist and the collision volume bone in order to achieve this result. What you're trying to achieve is called "twist joint" and usually needs to average the rotations between previous and next joint in the hierarchy. Animation triggers are not supported in SL (ie: if Wrist joint rotation >= X degrees run this animation, else run this other animation //// this is not supported in SL)

13 hours ago, agentronin said:

Does "through the length of the arm" mean the entire length of the arm from wrist to shoulder?

The local axis of a bone has a direction, and that is what i'm referring to. In Avastar it should be the local +X of said Collision Volume bone, which should rotate around this axis (which runs through the forearm along it length)

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And how exactly do you think to make 2 standalone animations to work together this way?

There is only one animation I am working on. I am not yet at the point where I need to synchronize two animations. I will be soon, and I plan to use PMAC 2.0 Builder's Kit to do it. At the moment I have an Avaster created avatar with SL bones in Blender to create an animation with. Its shape was downloaded from SL in a slider XML file and generated from my Slink Physique body. The Avaster created body in Blender is intended only to create an animation with. I do not intend to upload that body for use in SL.

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Good luck with this. You should know exactly how long the AO animations last and make suitable collision volume bone animations to go with it with perfect timing between yours an the AO's.

17 hours ago, agentronin said:

I will be soon, and I plan to use PMAC 2.0 Builder's Kit to do it

As far as i can tell from what i could look up on the web, that's an automation system to synch animations on sit and it is designed for OpenSim. I guess you're making your own mod version for this task

17 hours ago, agentronin said:

At the moment I have an Avaster created avatar with SL bones in Blender to create an animation with. Its shape was downloaded from SL in a slider XML file and generated from my Slink Physique body.

Although you can keep developing the weighting to include Collision Volume bones on this current avatar, the shape is given by the skeleton definition and it's not dependent from the mesh you were wearing at the moment of export. This shape gives you a good starting point but it won't include the actual weighting from the SlinkPhysique body, which is crucial in order to design your animation in this case, since the twist deformation would depend from that.

Your best bet would be to apply for a SLink devkit, bring it in Blender and attach it to avastar, make the arm twist set up and create your own animations. Synchronization will end up being a big pain and it's prone to error accumulation, which will ruin the effect overtime.

Anyway, good luck! :)

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Posted (edited)

I applied for the Slink Physique developers kit. Thanks for the tip :).

Now I am also concerned about the hands. They are from Vista Animations  "VISTA BENTO PROHAND SLINK MALE". My animations include a hand grabbing a post. Precision is needed here. Would I also need a similar kit from Vista Animations?

Edited by agentronin

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Precision is something that can be achieved only making an animation on the specific shape a character has. For this reason, i would suggest to override the whole arm and hands with your own animation. As far as i know, Vista doesn't supply devkits, but you'd do best to try and ask in their customer group. If one is available they would certainly know and point you to it.

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