On 09/30/2013 02:21 AM, cristupidmail wrote:
> Ok, the rest position of the vertex V, for example, is clear (pos_V[0]).
> Instead if I want to know the position of the vertex V in a certain time
> "1" (not binding time), which operation does OpenSG apply?
> Something like: pos_V[1] = mat_joint[1] * matBind ?
not exactly. The joint matrices are not indexed by time, but by joint
index (a samll number uniquely identifying the joint within the
skeleton). Every vertex has a number (usually <= 4) of joints that
influence it and as many weights that determine how strong the effect of
a joint on the vertex is [1]:
mat4x4 matJoints[N];
uint4 jointIdx;
float4 jointWeight;
float4 inPos; // vertex position in the mesh
float4 outPos = (0, 0, 0, 0);
for(i=0; i < 4; ++i)
{
outPos += jointWeight[i] * (matJoints[jointIdx[i]] * inPos);
}
This assumes the jointWeights have been properly normalized so that they
add up to 1 - otherwise you need to divide by the sum of the weights to
compensate.
The matrices in matJoints are themselves computed by multiplying all
joint matrices up to the root joint and then multiplying by the joint's
bind matrix. So assuming joint i has parents joint a and joint b:
matJoints[i] = joint[a].matrix * joint[b].matrix *
joint[i].matrix * joint[i].bindMatrix;
Hope it helps,
Carsten
[1] see the GLSL code in
Source/System/Dynamics/Skeleton/OSGGPUSkinningAlgorithm.cpp
[2] see
Source/System/Dynamics/Skeleton/OSGSkeletonJoint.cpp:jointUpdateEnter()
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