Linear blending skinning is popular for its very high performance,
but is prone to very well known artifacts: such as the loss of volume.
In addition geometric skinning does not generate contact when the joint bends,
but rather a smooth fold followed by self intersections.
Dual Quaternions skinning improve volume preservation,
but bulges the shape at joints,
does not generate contact and is also prone to self-intersections.
In practice we would like a skinning technique to generate contact when joints bend,
and preserve the rigid appearance articulated bodies in a plausible manner,
as shown in the video.
Our implicit skinning technique computed in real time,
enables interactive deformation while improving the realism of the results
over real-time state of the art approaches.
We start with standard inputs: the mesh and its animation skeleton, the skinning weights,
and the mesh's partition with respect to the skeleton's bones.
We precompute a field function whose 0.5 iso-surface approximate the mesh part
associated with each bone, then combined with implicit composition operators
to define an implicit surface approximating the whole mesh.
During the animation the mesh is deformed with geometric skinning,
while the field functions are rigidly transformed.
The Dual Quaternions solution is corrected by projecting the mesh's vertices
on the deformed iso-surface following the field function gradients.
Contact is performed in the folds.
Our method provide predefined parameters enabling artistic control of the resulting shape.
In this example we first show how the union operator produces a plausible deformation
at joints such as: elbows or knees.
The realism can be enhanced using the predefined gradient-based blending operator
that keeps the fold surface further from the joint, for large bending angles,
and produces a small blend for small angles.
Here again the union operator provides a plausible result.
A real finger joint generates a fold and contacts surounding by organic bulges.
This effect can be reproduced using the pre-defined gradient-based bulge-in-contact operator.
While the automatic settings provided with our method allow us to generate our results,
it can happen that a complicated joint is inadequatly partitionned.
A user interaction is then required to add or remove vertices from the set reconstructing the field function.
This is done with interactive feedback in our system.
We provide a set of preset parameters.
These parameters have been set intuitively using the interactive feedback
provided by our system when their values are modified.
Here we show the interactive preset of the bulge-in-contact composition operator.
We now demonstrate the robustness of our method when animating various characters.
The armadillo model is composed of more than a hundred and seventy thousand vertices.
The mesh is highly detailed and the joints have features
that make them very challenging to skin in a acceptable manner.
The knee is animated and skinned with our method at 36 frame per seconds.
At extreme postures Dual Quaternions produced deep self-intersections,
while our method generates the contacts and preserve details.
We now present several models with complete animations skinned with our method.
The number of bones and vertices of the models as well as the average frame rates
are given at the beginning of each animation.
Each animations includes a comparisons between: our method, Linear Blending and Dual Quaternions.