FXGear CTO KJ Choi (Kwangjin Choi) explained the main technology behind a very robust cloth simulator Qualoth.
FXGear CTO KJ Choi (Kwangjin Choi) explained the main technology behind a very robust cloth simulator Qualoth.
The core algorithm of Qualoth is based on the paper “Stable but responsive cloth” published in Proceedings of ACM SIGGRAPH 2002.
The main researcher of Qualoth is Kwang-Jin Choi, who is the first author of the paper.
As described in the paper mentioned above, the key feature of Qualoth is the outstanding stability of the numerical simulation.
It is achieved mainly by proper handling of the buckling instability inherent in thin structures like cloth.
Thanks to the strong numerical stability, fast and dynamic movements of cloth with complex collisions hardly break the solver, which lets users spend more time on the aesthetic aspects of the simulation results, not on fixing broken results.
Qualoth is a Maya plug-in, and takes polygon meshes as input.
Those input meshes are triangulated internally for dynamic cloth simulation.
The solver calculates stretch, shear and bending deformation energy of the triangulated polygons to solve the equation of motion for dynamic simulation.
The major material properties are the stiffness of each kind of deformation (stretch, shear, and bending).
The rest of the properties are damping, friction, drag, and hysteretic parameters..
To get the desired behavior of specific fabrics, you can adjust such parameters.
For example, to get cotton like material, use higher stretch and shear stiffness to get relatively rigid behavior, and non-zero hysteresis parameter to get history dependent crease effect.
To get silk like material, use lower stiffness, lower damping, and higher drag force to get more elastic and wavy behavior.
Qualoth is being widely used for production of 3D feature animations and visual effects for digital doubles in movies.
Some famous feature animations from world top class animation studios are using Qualoth for cloth simulation.
Though it is not aimed for real-time applications like games, Qualoth has been used for numerous game cinematics.
Qualoth has been around for almost a decade, and many big studios successfully integrated it to their pipelines.