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More than 2 influence bones on one vertex?

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Posted (edited)

Does it ever happen in day-to-day animation skinning, that you'd want a particular vertex to be influenced by more than two bones? 

If so, does that happen quite a lot, or rather rarely?

Edited by teutoburger

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Thanks! Very insightful. Interesting to cancel out bones in an LOD scheme. 

 

Yes - it happens regularly for a minority of vertices
 

 

Can you give an example of which bones / vertices that would be? i.e. in which area of anatomy? By bendy parts, you mean knees and elbows?

 

Which bones would be used to have influence on a knee..

I can see how it would be a "knee bone" and perhaps a "hip bone"(?)

But which other bones ?

Or did you specify more than one bone placed inside the knee itself? (i.e. one for rotation and one for translation or something?)

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The most complex part of a humanoid are usually the shoulders, which has is evident by the use of HUGE shoulder armour pieces to mask any problems there. Equally or more difficult  would probably be the hip / thigh area, however most games get away with a small range of motions there (walking, running, jumping). But when your character is supposed to do Yoga poses, then these areas will become critical.

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It depends mostly on the detail of the skelton.

A detailed skeleton often has helper bones to limit bad deformations from the skinning technique, which itself does not simulate sliding skin, volume preseravation, muscle bulges...

So it helps to add additional bones e.g. at the joint positions and in the middle of real bones, interpolating rotation to get better results.

Also very difficult areas are sholders and that butt :)

Using helper bones a maximum of 4 bones per vertex becomes already a problem.

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HUGE shoulder armour pieces to mask any problems there

 

that's a fun fact! :-) 

I always wondered why WoW avatars have entire towers including battlements, on their shoulders.

 

sholders and that butt

hip / thigh area
 

So it's maybe caused by the degrees of freedom a shoulder and a hip joint allow. 

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So it's maybe caused by the degrees of freedom a shoulder and a hip joint allow.

 

Indirectly said, yes. But the real reason is: The body uses more visible muscles to achieve those degrees of freedom, and also the resulting movements cause parts of the bone to become visible through the skin in certain cases, so these areas are impossible to handle with just 2 bones.

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