Houdini 20.5 Nodes Dynamics nodes

dynamics node

The Cloth Solver can be used to simulate garments that interact with animated characters. The following guidelines will help you achieve good results.

The cloth geometry can consist of triangles, quads, or a mix of triangles and quads. If your geometry consists mainly of triangles, then you should provide uv coordinates, by creating a uv vertex or point attribute of size 3. The u and v directions represent the warped and weft directions of the cloth, respectively. When you have a quad mesh, you can omit specifying uv coordinates, if you want. In that case, the solver will use the directions of the quad edges as the warped and weft directions of the fabric.

You should not use polygons with five edges or more. If you want to use polygons that have more than four edges, then you can divide these up into quads and triangles using the PolyDoctor SOP.

A common beginner mistake is to create a thick piece of cloth as two layers of geometry: always create a single layer. Instead, use the Collision Radius to create a separation between a piece of cloth and the objects that it is in contact with.

You can achieve the best looking results when the triangles in your geometry are roughly equilateral and the quads are roughly square shaped. Long, stretched out triangles and quads can cause collision problems and can result in unnatural looking simulations. You will get the best results when all the triangles and quads in your cloth geometry gradually vary in size over the surface. You should avoid having large polygons connected to much smaller polygons.

Make sure you don’t have points in nearly the same position, because it creates self-collision problems. You should either remove or fuse those points.

Note

The Fuse SOP tends to create polygons in which the same point occurs multiple times as a vertex, which is also very bad for cloth simulation. The PolyDoctor SOP can help fix this problem.

In your cloth geometry, you should avoid edges that are very small compared to neighboring edges. Such small edges tend to increase the amount of adaptive substepping, which is required to keep your simulation stable and accurate. This substepping is based on the relative amount of stretch that may happen on any edge in the geometry. The presence of a single very small edge will cause a high level of substepping, which can cause the simulation time to become very high. The PolyDoctor SOP can help you find and fix very short edges.

Dynamics nodes