A Study Of Cloth Simulation And Model Based On Position-based Dynamics

Cloth animation technology, with its never fading charms, has a history of nearly thirty years in the field of computer graphics and now-days many researchers still focus their attention on it because it has been widely used in computer animation, 3D games, film special effects, virtual reality and so on. Especially in the present when the technology of computer hardware and software develop rapidly, some real-time interactive applications require higher and higher simulated quality and speed of cloth animation technology. In order to realize the simulated target of cloth animation being fast, stable and real to meet the growing demands of people, how to build a simple and efficient cloth model and which algorithm of collision detection should be chosen have become urgent problems for the researchers.Embarked from the cloth animation based on physics, in comparison of the advantages and disadvantages of commonly used cloth modeling technology, this paper mainly studies the cloth animation modeling technology in the basis of the Position-based Dynamics which has the characteristics of being stable, rapid and easy to control. In the thorough analysis of the constrained dynamics model in Position-based Dynamics, this paper proposes a new angle bending constraint model as a substitute for the original dihedral bending constraint model, to simulate the effect of bending deformation of material. At the same time, it also improves the collision detection algorithm. Including:1) first of all, a method of constructing virtual triangle is discussed. It can be applied to any form of cloth mesh subdivision model, and find the very only corresponding virtual triangle for every vertex of the cloth model. Then we can easily simulate the bending behavior of fabric by creating bending constraint model in the maximum angle of the virtual triangle, which makes cloth simulation no longer depend on the geometry model of fabric topology structure and that means wider application scope and not being confined to the grid model in the form of triangles any more.2)Based on the theory of Position-based Dynamics, we proposes a novel method of constructing bending angle constraint model which solves the problems that theconvergence speed of the dihedral angle bending model is slow and bending detail simulation effect is not obvious. This model reduces the computational cost by narrowing the constraint range of the bend model from a pair of edge shared triangle down to a virtual triangle. Meanwhile, in the light of the common problem of symmetry for the dihedral angle bending constraint model and triangle bending constraint mode, it introduces the signed triangle area which improves the quality of cloth animation.3)We analyze the difference of collision detection algorithm between rigid and deformable objects and present the optimized spatial hashing for collision detection of deformable objects. The solution is aimed to figure out the collisions and self collisions by combining the bounding volume hierarchies and spatial partitioning. We change the representation of the axis-aligned bounding boxes by “center-radius” to save the cost of storage, thus, it can enhance the efficiency of collision detection. The methods proposed in this paper have a certain degree of theoretical innovation, and it works very well in cloth simulation.