目的 现有刚体破碎仿真模拟中，基于物理受力分析的方法往往难以应用在对实时性要求较高的场景中；而基于非物理方法的破碎模拟，破碎效果大多缺乏多样性。为了使得破碎模拟同时满足实时性和破碎效果多样化，提出了一种多样化实时刚体破碎模拟方法。方法 进行破碎模拟时首先由选定的种子点生成类型得到种子点集，采用Sweep Plane算法生成 Voronoi 图后基于Voronoi图信息对模型进行空间剖分；然后选择破碎时行为模拟方式，对物体破碎时所受外力进行模拟；最后对破碎时碰撞检测及碰撞后碎片的运动过程进行模拟并渲染显示。结果 通过组合不同的种子点生成类型和破碎时行为模拟方式，得到了多样化的刚体破碎效果，对单个刚体进行破碎模拟时，碎片数目不超过200个时帧率可以达到75帧/s，满足实时性的需求；对多个可破碎目标同时存在的复杂场景，破碎仿真模拟的平均帧率可以达到50帧/s，同样满足实时性要求；与现有方法对比的结果也验证了本文方法在计算效率和破碎效果多样性两方面达到了较好的平衡。 结论 本文方法在满足实时性要求的同时，丰富了刚体破碎的效果，不同种子点生成类型和破碎时行为模拟方式的组合可以实现破碎效果多样性。
Diversified real-time fracturing simulation of rigid body
Lv Chang Jian,Cao Li,Huo Jing Ze,Liu Xiao Ping(School of Computer and Information, Hefei University of Technology)
Abstract: Objective Fracturing has been widely applied in video games, films and other industries. And fracturing simulation has attracted increasing attention in the field of computer graphics. Particularly, with the rapid development of virtual reality over the past few years, greater demands have been placed on the diversity of fracturing results and real-time fracturing in a virtual scene, better fracturing result could significantly strengthen the realistic experience of players. In physics-based simulation method, the work of rigid body fracture simulation has been gradually carried out from the early inelastic deformation model to simulate the inelastic behavior to the mass-spring model and then to the fracture mechanism based on tetrahedral model. In order to improve the realistic sense of fracturing effect as much as possible, many scholars are also devoted to enriching the detail expression of crack during fracturing. During the continuous exploration of the simulation of the physical phenomena in the real world, several physics engines have appeared in succession to simulate the phenomena of fragmentation and explosion in various real worlds. In recent years, great progress has also been made in the simulation of the fragmentation of thin-plate type materials such as paper; all these make the real-life fracturing phenomenon more varied in the computer. In the non-physical method of rigid body fracturing, the Voronoi diagram based fracturing method plays a main role. However, the rigid body fracturing method still has some disadvantages: First, the method based on physical force analysis does not work well in the situation where real-time is highly demanded and the instant fracturing effect produced by the fracturing simulation based on non-physical method lacks diversity. Second, in most games, models often have been pre-fractured during their authoring time, when fracturing occurs, the original models are simply replaced by the pre-fractured one, this kind of method greatly increased authoring time of the designer and reduce the diversity. Most of the earlier works in film use the miniature model to simulate the crushing of large-scale scenes, such as the collapse of high-rise buildings, this kind of method also has the problem of lack of realism; In order to obtain real-time fracturing and diversified effects in fracturing simulation, a method applicable to diversified types is proposed, namely a real-time rigid body fracturing method. Method During the fracturing simulation, the type of seeds generating (there are three types of seeds generation: type of completely random, type of evenly distributed with disturbance and type of radiation) should be chosen first, then using Sweep Plane algorithm to generate the Voronoi diagram, based on which space partition will be carried out on the model. During this process, in order to avoid the situation in which the seed points concentrated in a local area too much or worse in the global area, a sparse processing has been introduced: when multiple seed points are separated from each other by a certain threshold, the average value of the position of these seed points will selected as one seed point. And then, by means of a simulation pattern of fracture behavior (two types of simulation pattern: type of explosion and type of collapse), the external force when rigid-body fracturing will be simulated and collision detection, following impact process of the broken fragments will be simulated too. Finally, it goes on the rendering and display. Result Via combination of different seed point generating types and simulation patterns of fracture behavior, diversified effect of fracturing will be simulated. The real-time requirement can be satisfied: in a single rigid body model fracturing simulation, the frame rate can reach 75 fps (frame per second) with 200 broken fragments; in more complex scenarios (e.g. a building) where there are about 150 fracturing objectives with 3 types materials, the frame rate can also reach 50 fps, in order to make the fracturing effect in such a complex situation, not only to meet the diversity of fracturing effect, but also to meet the real-time requirements, in the fracturing of different building components using different fracturing simulation type, through the combination of different types of seed point generation and fracture behavior simulation, and a number of less affected parts from each other are broken at the same time. After comparing with some existing methods, it also approves that the method in this article will achieve a better balance between computational efficiency (compared to physics-based method) and diversity of fracturing effects (compared to Voronoi-based method). Conclusion A real-time rigid body fracturing method applicable to multi fracturing effect is proposed in this paper. On the one hand, this method possesses a real-time feature, and on the other hand, it also contributes to enhance the diversity of rigid body fracturing. By the combination of different seed point generating types and simulation patterns of fracture behavior, diversified fracturing effects can be achieved. In the future work, this method will be further improved and optimized to be applied to more complicated fracturing simulation.