Simulating Cloth
By Andy Pierce and Jernej Barbic
1
Cloth simulation overview
• Problem of interest
• Applications
• Challenges – Forces
•
– Deformation
“Large Steps in
Cloth Simulation”
[Baraff and Witkin 1998]
2
Forces and stiffness matrices
• Cloth Forces – Stretch
– Shear – Bend
• Bend Formula
• Force Derivatives
[Baraff and Witkin 1998]
Θ
N1 N2
3
Timestepping the forces
Explicit
– Fast
– Unstablewithlargetimesteps
Implicit
[Baraff and Witkin 1998]
– Mustsolvesparselinearsystem – Cantakelargetimesteps
4
Challenges
• Complexity of Formulas – 3rd order tensors
– Large matrices
• Collapsing Triangles – Length of normal -> 0 – Explosions
5
Results
6
Model
Triangles
FPS
% Forces + Stiffness Matrix
% Solver
Curtain
2400
25
67
33
7
Model
Triangles
FPS
% Forces + Stiffness Matrix
% Solver
Curtain
2400
25
67
33
8
Model
Triangles
FPS
% Forces + Stiffness Matrix
% Solver
Skirt
4608
12
75
25
9
Multithreading
Force and Stiffness Matrix Computation
50
45
40
35
30
25
20
15
10
5
0
12345678
Number of Threads
10
Milliseconds
Other considerations
• Damping Forces
• Collision Detection
[Bridson et al. 2002]
• Code Optimizations
[Govindaraju et al. 2005]
11