[Figure 3] Top row of vertices selected for conversion to a Nail Constraint.

4. Select Syflex > Constraints > Nail. This acts as the waist. The syNail1Trs node can be animated. It is the basis for our spinning and swirling skirt motion.
Save your work.

5. Load the scene dancing_skirt.mb, which is located on the companion DVD. This scene has the syNail1Trs node animated over 300 frames. The animated hip translation and rotation gives the skirt a nice dynamic dancing quality.

6. Run the simulation. The animated hip gyration gives the cloth quite a ride, but as shown in Figure 4, the cloth does a nice job of keeping up with the motion.

A bit of maintenance is needed for the cloth to act more realistically. Figure 5 shows the cloth spinning in on itself, causing severe intersecting geometry, and the polygons are visible in the final render. The skirt could be further subdivided or polygons could be smoothed, but the geometry can also be replaced with something more render-friendly and flexible.

[Figure 4] Frame 220 of the test simulation.

Rewind the Timeslider to the beginning frame. We are going to use a relatively low-polygon animated skirt as a proxy that will drive a more realistic subdivision surface model.

1. With the syCloth1ShapeTrf mesh node highlighted, create a subdiv surface duplicate, making sure to keep the original selected, as shown in Figure 6.

2. With the polygon skirt selected, go to the top of the Maya menus and select Modify > Convert > NURBS to Subdiv to create the subdivision surface duplicate of the skirt.

This subdiv duplicate is driven by the original low-polygon cloth animation with a wrap deformer. Maya has several types of deformers to choose from. Deformers give you the ability to smoothly contort or deform geometry in a variety of ways. Deformers serve many purposes and are infinitely useful in creating animation that might otherwise be impossible by other means.

1. This can be done by selecting the new polyToSubd1 node and then the syCloth1ShapeTrf node. The order is important.

2. Amidst the Maya menus in the Animation menu set, select Create Deformers > Wrap. The subdiv surface model is now deformed by the cloth.

3. We must now hide the syCloth1ShapeTrf node by making it invisible. Select syCloth1ShapeTrf in the outliner and turn off visibility as shown in Figure 7. What remains is the subdiv copy of the skirt ready to render (see Figure 8).

[Figure 5] Polygons visible in a mental ray render.	[Figure 6] Creating a subdiv duplicate of the polygon mesh skirt.