CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Linear Blend Skinning (LBS)

Acknowledgement: Daniele Panozzo, Alec Jacobson

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

LBS generalizes to different handle types

skeletons regions points cages

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Linear Blend Skinning rigging preferred for its real-time performance

place handles in shape

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Linear Blend Skinning rigging preferred for its real-time performance

place handles in shape paint weights

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Linear Blend Skinning rigging preferred for its real-time performance

place handles in shape paint weights deform handles

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Linear Blend Skinning rigging preferred for its real-time performance

place handles in shape paint weights deform handles

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Linear Blend Skinning rigging preferred for its real-time performance

place handles in shape paint weights deform handles

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Challenges with LBS

• Weight functions wj• Can be manually painted or

automatically generated• Degrees of freedom Tj

• Exposed to the user (possibly with a kinematic chain)

• Richness of achievable deformations

• Want to avoid common pitfalls – candy wrapper, collapses

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Properties of the Weights

Handle vertices

Interpolation of handlesPartition of unity

is linear along cage faces

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Weights Should Be Positive

Unconstrained biharmonic[Botsch and Kobbelt 2004]

Bounded Biharmonic Weights[Jacobson et al. 2011]

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Weights Should Be Smooth

Bounded Biharmonic Weights

Extension of Harmonic Coordinates[Joshi et al. 2005]

[Jacobson et al. 2011]

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Weights Should Be Smooth

Bounded Biharmonic Weights Extension of Harmonic Coordinates[Joshi et al. 2005]

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Different Types of Handles

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Bounded biharmonic weights enforce properties as constraints to minimization

is linear along cage faces

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Bounded biharmonic weights enforce properties as constraints to minimization

is linear along cage faces

Constant inequality constraints

Partition of unity

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Bounded biharmonic weights enforce properties as constraints to minimization

is linear along cage faces

Constant inequality constraints

Solve independently and normalize

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Bounded biharmonic weights enforce properties as constraints to minimization

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Bounded biharmonic weights enforce properties as constraints to minimization

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Bounded biharmonic weights enforce properties as constraints to minimization

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Some examples of LBS in action

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Some examples of LBS in action

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Some examples of LBS in action

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

3D Characters

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Mixing different handle types

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Skinning Decomposition for Rigid Bones

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

Skinning Decomposition for Skeletons

CAP 5726 - Computer Graphics - Fall 18 – Xifeng Gao Florida State University

ReferencesFundamentals of Computer Graphics, Fourth Edition 4th Edition by Steve Marschner, Peter ShirleyChapter 16

Skinning: Real-time Shape DeformationACM SIGGRAPH 2014 Coursehttp://skinning.org