Cloth in AM ~ Cloth Constraints

• CLOTH IN AM

  Getting started with learning cloth in Animation:Master

• INTRODUCTION

  Part 2: Defining terms.

• HOW AM CLOTH WORKS

  Part 3: The Cloth Wizard does its magic.

• COLLISION DETECTION

  Part 4: Cloth interacting with other objects.

• CLOTH CONSTRAINTS

  Part 5: Mass to CP / CP to Mass Constraints

• SUSPENSION CPS

  Part 6: Giving control back to the bones.

Dec 5, 2003 at 3:04 PM

AM Cloth creates two constraints nowhere else available in the software (i.e. you, the user, can only make use of these constraints via the Cloth Wizard). The first you’ve already seen, the CP to Mass Constraint. In the Splines Folder of the Action, if you expand it enough to see the individual CPs, you can see that each CP is constrained to one particular Mass. Those Masses have been subsequently created at the location of each CP in the group you wanted to have the Cloth Wizard applied to.

The second we haven’t encountered yet, but is the key to controlling Cloth animation, the Mass to CP constraint.

Let’s charge right in and see it in action. Go to your Action and delete all the Cloth information: the Action Objects Folder, the Splines Folder and the Spring System under the Objects heading in the PWS. Go into Muscle Mode and select only the right half of the model. Right Click the Group and select the Cloth Wizard. Go to Frame 0 and simulate.

The Cloth has not broken away from the model and is starting to respond directly to bone movement.

Now the Cloth is behaving much better. Even though the right half has fallen, attracted by gravity, it has not broken away from the model and into oblivion. This is because of the Mass to CP Constraint. Go back to Frame 0 and into the top view. Click on Dynamics Mode. You should now see on the right hand side of the model, the same sort of Mass and Spring network you saw earlier. But in the row of CPs just outside of the group you applied the Cloth Wizard to has a different representation. Instead of small red pixel, it’s an empty red box surrounding a CP. If you now expand the Action Objects, Spring System and Masses in the Action, you can see that not every Mass has a keyframe on it. In fact, they don’t have any. If you expand one of those you can see that they have a “Mass to CP” Constraint applied to them, and these are represented by the small red box in Dynamics mode.

The Mass to CP Constraint anchors the Cloth to the rest of the model and, consequently, to bone movement.

The Mass to CP constraint allows the Spring System to be bound to the parts of the mesh that are not part of the Cloth group. Those Masses stay fixed relative to their CPs and underlying bone structure but are connected via springs to the free Masses of the Cloth group. In other words, even though they are fixed relative to their bones and follow only what the bone does, they exert influence over the rest of the Cloth by virtue of being connected to them via springs.

Let’s apply this toward affecting the whole model and not just one half of it. After all, the animation itself is rather lackluster – the left side is just stiff and the right side just droops and flails about.