Dynamic Simulation Of Cloth Based On Position Based Dynamics

With the development of computer graphics and the popularization of the computer,the virtual world built by them has penetrated into all aspects of people's life,especially in the field of movies and games.The fabric simulation is an important part of the virtual world to build,realistic fabric simulation can greatly enhance the reality of the virtual environment,and improve the entertainment experience.However,it is difficult to make a good fabric simulation because of it's changeable characteristic.In order to get realistic,fast and stable cloth simulation to meet the requirements of real-time interactive applications,many scholars at home and abroad have devoted themselves to the research of cloth simulation and obtained some research results.In this thesis,the physical methods used in the fabric simulation are compared and the Position Based Dynamics(PBD)is selected as the basis of the simulation research because the method has the advantages of fast,stable and easy to control.In this thesis,we study the PBD in details and find that the order of constraint adjustment depends only on the data structure.Based on the detailed analysis of the movement of the real world fabric and the propagation of the force,the order of constraint adjustment based on fixed point propagation is proposed.This method simulates the process of cloth action under the external force.Firstly,the order of the particle processing is sorted by the breadth-first search from the fixed point depending on the fabric topology.And then the particle-related constraints are sorted according to the order of the particle processing.Based on this order,the blind iterative calculation is avoided in the simulation of the shape changes.The simulation results are compared with those without using the proposed method,the more realistic simulation results are obtained and the convergence efficiency is improved.In order to simulate the motion of the fabric,it is necessary to use the numerical solution method to solve the particle motion equation.In this thesis,we study the several commonly used numerical integration methods,and the Verlet integral method is analyzed.For the speed synchronization problem of Verlet,we choose the Velocity-Verlet method instead as the numerical solution method.For the defect that it is not suitable for the calculation of the PBD,the calculation form suitable for the PBD is derived,and the accuracy of the method is not lower than that of the Velocity-Verlet without increasing the computational complexity.In addition,the method assumes that acceleration only depends on position,and does not depend on velocity.For this problem,the improvement is given from the two aspects of the simplified mechanics model and the speed prediction and correction.In order to prevent the fabric from penetrating after contact with other objects,it is necessary to detect and respond to collisions in the virtual world to conform to the physical reality.In this thesis,In this thesis,Bounding Volume Hierarchy(BVH)method is used for collision detection based on spatial coherency.First of all,use the sort and sweep algorithm in the top of the bounding box to exclude disjoint objects,,avoiding the two-two intersection tests when existing multiple objects.Then make more accurate collision detection by using BVH.And in this step,optimize the processing of the bounding box tree structure and traversal method to improve the efficiency.