【摘要】 快速真实地模拟树在风中的摇曳一直是图形学中的一个挑战性问题.已有的方法,或者计算速度太慢,或者所处理的模型局限在几千个面片之内,难以用较强的真实感进行动画模拟.针对复杂树在风中的自然摇曳,该文提出一种新的方法.一方面,它基于统计数据采用高斯分布来近似逼近实际风力,既可以基于物理性态很好地反映风力的影响,又可以方便树的变形计算;另一方面,根据树的层次结构特点,新方法对树的各个部分分别进行独立的变形计算,然后再根据它们的连接关系进行组合,完整地获得树的变形.新方法对于小振幅的非末梢枝条,是利用静力分析来计算它们的变形,而对于振幅大的末梢枝条则采用Newmark逐步积分法求解其振动方程,这样就可以以较少的计算开销获得变形真实感很强的结果.在对树的各种姿态进行成像时,新方法运用了基于硬件的shadowmapping技术和LOD(LevelOfDetails)技术,以快速生成高度真实感的树.实验表明,对于有近4万个控制节点、近90万个拟合外观模型的三角形的柳树模型,新方法可以对其自然摇曳进行每秒0.6帧的高度真实感的模拟.更多还原

【Abstract】 Fast and realistically simulating the tree swaying in wind is still a challenge topic in computer graphics. For the existing methods, some are slow for deformation computation and some can handle only simple tree models, which is difficult to achieve high realistic impression for the tree swaying in wind. This paper presents a new method emphasizing on accelerating the computation for the physically based deformation of the complex tree model so that the tree swaying in wind can be simulated in high efficiency. On the one hand, it employs a wind model based on the real wind law through the Gauss distribution so that the turbulent effect on the tree can be fast computed. On the other hand, it speeds up the deformation computation for the whole tree by first calculating its branch deformation respectively and then assembling the deformation of the branches based on the links between them. To fast compute the branch deformation, the non-end branch with little amplitude is analyzed statically to deform, while the end branch is deformed by solving its dynamic response with the Newmark step-wise integration method. In rendering, the new method takes full advantages of the hardware-based shadow mapping and level-of-details (LOD) techniques for fast producing the realistic images of the tree. Experimental results show that the new method can fast and realistically simulate the tree swaying in wind for a complex willow model in nearly 40 thousand control nodes and 09 million triangles.更多还原