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vex matrix influence


Juraj

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Hello,
I am trying to create simple binding in VEX. I want to bind geometry to Nulls, which will be animated.

I think that idea is to get transformation matrix of nearby null and multiply its position by it. It works quite well for "parent" nulls influencing whole transformation.

However I need to do localized binding - influence of matrix is modulated with distance to the null. One approach would be to lerp between original position and transformed position. But I need to stay with matrices. So I need to create "influence" matrix. Something, which will blend to identity matrix in far areas from null.

I am not sure how mathematically it should be solved. How does it work in maya's binding? I guess each point iterates over all joints it is influenced by and its position is multiplied by those joint transformation matrices but that is somehow masked (by skinning weights which are painted / computed on distance etc) .

One solution that struck me would be to break 4x4 transformation matrix into translation offset vector (which I can blend just by multiplying with 0) and into 3x3 orientation matrix (which I can convert to quaternion and slerp that with identy quaternion ). I think it should work. I am wondering however if there is more correct way of doing this.

Also if you know some resources where such things are explained please point me to them :)

Juraj

 

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