布料解算插件 Qualoth 重点参数分享

　　前言

　　Qualoth是韩国FXGear公司推出的一款布料模拟插件，可以计算出很自然的衣褶以及动态效果，并且能应对大幅度动作的碰撞解算，可以和Houdini的Cloth Solver相媲美；

　　目前这款插件的教程很少，只能找到一个冗长的韩文视频以及官方帮助文档，没有其他更详细的教程；

　　我下载了for Maya的版本体验了一段时间，摸索出大体的制作流程，现分享如下；

　　制作流程

　　Qualoth的制作流程和nCloth差别较大，主要是前期衣物建模流程的不同，前几步类似传统服装制作：

　　1、先用Curve曲线根据真实的服装板式图“打样“；

　　2、线条两两生成Pattern，依次把整件服装的所有面片都生成好；

　　3、再把接缝处的曲线进行Seam缝合，；

　　4、开始局部模拟，使衣服适配人体模型；

　　5、接着设置缓存路径和缓存名；

　　6、Play开始模拟就可以了~

　　在布料参数设置方面，可以先保持默认，但需要把Solver下的几个参数重点设置一下：

　　重点参数

　　测试发现，以下几个参数对解算效果的影响最大，请仔细参考数值范围：

　　Frame Samples：

The number of sub steps to compute a frame. Using bigger numbers results in better accuracy in collision handling at the cost of increased computation time. ~ is reasonable for slow motions, ~ can be used for fast motions.

Frame
Frame  
 
Frame 1.5
Frame
Frame 
 
Frame 1.5
Simple Subsampling
Exact Subsampling

　　Time Scale：

The time stretching factor. This value scales the time unit used in Maya. Suppose that one frame corresponds to / seconds in Maya, and if you set “Time Scale” to 10.0, one frame is interpreted as / seconds by the solver. You can create slow motion effect (bullet time effect) by controlling this value.

　　Length Scale：

The length scale makes the cloth objects under this solver look bigger or smaller than the actual size which is represented by the geometry. Note that each cloth object has “Length Scale” attribute and “Length Scale Map”. The final effective length scale of a cloth vertex is calculated as follows. Effective length scale = Cloth Length Scale X Cloth Length Scale Map X Solver Length Scale

　　MAX CG Iteration：

The maximum number of iterations for dynamics computation. To obtain the best results, do not let the solver hit this limit. You can verify the number of iterations used at each frame in the printed solver statistics (#CG)

　　CG Accuracy：

The accuracy index for dynamics iterations. As this value gets bigger, more accurate results are obtained at the cost of increased number of iterations. ~ are reasonable for not-stiff cloth, and use ~ for stiff cloth. Values greater than  are not recommended。

　　动力场

　　Qualoth也可以受Maya动力场的影响，具体操作如下：

. Create a Maya field while selecting nothing. Do not select the cloth mesh at this time. See Fig.  -.
. Select cloth vertices (not the mesh) to be affected by the field, and then select the field node.   (The selection order is important). See Fig. -.
. Click “Qualoth>Connect Objects>Field>As Velocity”.
. A field filter node is created and now you can edit the properties of the node. (Fig. -)

　　经验总结

　　如果模型组是用Maya的默认方式制作衣物模型，Qualoth解算出来的效果会比较僵硬，自然的衣褶效果也很难体现出来，所以最好让模型组采用Qualoth的制作流程，使用Curve给衣服建立“打样”线条，这样才能获得更自然的效果，这一点在Houdini的Cloth Solver中也一样。