{"id":1096,"date":"2016-06-01T23:02:34","date_gmt":"2016-06-01T23:02:34","guid":{"rendered":"http:\/\/avastar.online\/?page_id=1096"},"modified":"2022-05-12T21:00:06","modified_gmt":"2022-05-12T21:00:06","slug":"bone-weights","status":"publish","type":"page","link":"https:\/\/avalab.org\/avastar\/300\/reference\/usermanual\/attachments\/bone-weights\/","title":{"rendered":"Bone Inheritance"},"content":{"rendered":"

<\/image> Bone Weights and Inheritance<\/span><\/h2>\n

Skeletal animation relies on inheritance: A weight on a bone at the end of a bone chain affects all movements induced by any of the bones in the chain. I can explain this best with an example:<\/p>\n

Theory corner: Weight inheritance and Collision Volumes<\/h3>
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Weighting the hands<\/h4>\n
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Think about the Hand part of your character. The Secondlife System, character has its hands weighted only to the Wrist bones. Only near the joint to the lower elbow bones we see that a few vertices have 2 weights distributed between the wrist and the lower elbow bone (the green zone in the image)<\/p>\n<\/div>\n

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Bone inheritance<\/h4>\n

Now you can rotate the wrist bone relative to the lower arms. Then the mesh moves along with the bone (on the red areas) and behaves well near the joint (on the green areas, stretches without getting too distorted)<\/p>\n

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But when you move the lower arms instead of the wrist bones, then the hands still move along with the arms, although most vertices are only weighted to the wrist bones! This is because the Wrist bones are children of the Elbow Bones. When the elbow bones move, then also the wrist bones move (because of the bone hierarchy). And because the fingers are weighted to the wrist bone, they move correctly along with the arm.<\/p>\n<\/div>\n

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Typical Weight count<\/h4>\n
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When you put all of this together then you realize that most of your vertices have only one weight (indicated as red area), while near the joints the vertices typically have no more than 2 weights. In fact we have seen above that the original SL Avatar has no vertex weighted to more than 2 bones.<\/p>\n<\/div>\n

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Green areas have 2 weights on each vertex<\/p><\/div>\n<\/div>\n<\/div>\n

And when you look in more detail then you see that the areas where a vertex has 2 weights are always close to the joints. Does this make sense now?<\/p>\n

<\/image> Basics of Fitted Mesh<\/h2>\n

This page is about the principles of fitted Mesh. We strongly recommend that you first read this page before you attempt to go ahead and do practical work. However here are the links to the other pages on this topic:<\/p>\n

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\nHow to work with the Fitting Panel<\/span><\/a>\n<\/div>\n
\nHow to work with Joint Positions<\/span><\/a>\n<\/div>\n<\/div>\n

The Nuts & Bolts<\/h2>\n
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When we step into fitted mesh the situation gets a bit more complicated. Technically Fitted mesh is nothing special. It just makes use of a subset of the Skeleton, namely the set of Collision Volume Bones, where each Collision Volume Bone is clamped to a corresponding classic bone. Thus building tightly coupled Bone Pairs.<\/p>\n<\/div>\n

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In the image aside you see for example the 3 bone pairs:<\/p>\n