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REAL-TIME CLOTH SIMULATION Researches: Javier Rodríguez-Navarro, Antonio Susín Early works are essentially devoted to the modelling aspects. Papers by Terzopoulos et al. [TPB87], [TF88] where the first physically-based ones. Other approaches on the dynamic modelling have been: particle-based models from the works of Breen et al. [BHW94] and Eberhardt et al. [EWS96], the energy-based models from Carignan et al. [CYT92] and Baraff and Witkin [BW98]. The most successful approach in modelling has been the mass-spring one, introduced by Provot [Pro95]. Like in other graphics topics, the efficiency of an implementation is related both with the chosen model and the hardware performance. Moreover, a trade-off between speed and precision has to be assumed, the work of Hauth and Etzmuss [HE01], and the one of Volino and Magnenat-Thalmann [VMT01] discuss the convenience of numerical integrators. The final decision for choosing one simulation model or another is mainly related with the final application field, for video-games or films the requirements are totally different. The work of Jacobsen [Jac01] for the game industry has been the pioneer in introducing a dynamic model for the cloth together with the numerical integrator, the Verlet method, which is suitable for GPU implementations. The first GPU cloth implementation is due to S.Green [Gr03], a structured rectangular mesh cloth and a solid sphere are simulated using Verlet method on the GPU. Only stretch forces have been simulated. For dealing with collisions on the GPU image based methods are introduced by Vassilev et al. [VSC01] for walking humanoids without dealing with occlusions. Others recent papers by Kolb et al. [KJ01], [KLR04] studies collisions with complex but static objects.
Fig 3. Local virtual camera distribution (left). Depth and normal maps from two cameras are used for dealing with collisions. Müller et al. [MDM02] presented a Finite Element Method (FEM) based approach for real-time deformations on the CPU. By estimating the rotational part of the deformation and using linear elasticity, they create plausible animations free of the disturbing artefacts present in linear models and faster than non-linear models. Teschner et al. [THM04] perform deformations on low resolution tetrahedral meshes, coupled with high resolution surface meshes used to visualize the deformed body. FEM methods applied to cloths use typically non-linear elements, because textiles are very flexible and bend easily, forcing deformation being modelled by the Green's strain tensor. Eztmuss [EKS03] introduce a FEM linear method that can be applied for large deformations using rotation correction directly deduced from the non-linear Green's tensor.
We have developed a complete GPU based methodology for unstructured cloth meshes in this way we have incorporated FEM to the simulations to reach more realism and we will study the possible applications in both animation and engineering worlds. The whole animation is working on the GPU, so both collision and self-collision detection are implemented on the GPU and we have also incorporate the character motion for dealing with cloth-character interaction.
Fig 4. Complete animation on the GPU. FEM is used for cloth modelling. Collisions and self-collisions are also implemented. Rodríguez-Navarro J., A. Susín. Rodríguez-Navarro J., M. Sainz, Susín A. Rodríguez-Navarro J., M. Sainz, Susín A.
References: [BW98] Baraff, D. and Witkin, A. (1998). Large steps in cloth simulation. Computer Graphics Proceedings, Annual Conference Series, 98: 3--54, 1998. [Jac01] Jacobsen T., Advanced Character Physics. Proc. Game Developers Conference'01, 1--10, 2001 |
