一种有效的隐式约束动力学布料动画方法

Cloth Animation Based on Implicit Constraint Dynamics

布料动画中,通常采用施加约束的方式限制布料的过度拉伸.已有的研究工作没有充分考虑拉伸约束与弯曲形变之间的关系,构造的动画模型并不完善,无法模拟布料无拉伸而多褶皱的"刚柔"相混的复杂变形效果.针对此问题,提出一种基于隐式约束力的布料动画方法.首先,建立有效的布料弯曲受力模型,并提出一种动态适应性约束方法,能够同时处理布料运动过程中结构和剪切2种不同类型的拉伸,避免单一结构拉伸约束导致的"过剪切"变形或者过约束导致的"刚性"失真效果;建立碰撞约束,避免局部调整穿透质点引起的过度拉伸问题.其次,将各种约束以隐式约束力的形式增加到动力学系统中,采用约束型迭代精化的方法进行求解.实验结果表明,该方法稳定有效,能够在保持布料弯曲形变的前提下,将拉伸控制在合理范围内,真实地刻画布料"易弯抗拉"的变形特征,实现逼真的布料变形动画模拟.

Cloth animation has been one of the hottest topics in the field of computer graphics for many years. Simulating inextensible cloth with wrinkles is one of the challenges. To prevent the overstretching in cloth animation, effective constraints are usually introduced into the system. However, existing cloth solvers have established the constraints in disregard of the relationship between stretching and bending deformation, so that the final animation is not satisfactory. In this paper, a novel method of cloth animation based on implicit constraint dynamics is proposed. Firstly, the bending deformation of cloth is analyzed from micro-mesh view, based on which an adaptive constraint is established to structure and shear tensile. By applying the constraints, over-elongation deformation can be avoided while wrinkles are not prevented on cloth. At the same time, global collision constraints are established to prevent the penetration, which can avoid the over-elongation that can be easily caused by locally moving particles. Secondly, constraint dynamic equation including implicit constraints is developed that is solved by constraint manifold iterative refinement method. Finally, experiments are conducted and the analysis and evaluation are given. The results show that our method is stable and effective, which ensures the realistic and effective cloth simulation.