techdocanimclothes2012

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Rigging Clothes for Animation inThe Place Where Lost Things Go

Technical Document

Ethan Shilling

A Flock of Pixels

aockofpixels.blogspot.com

25 / 05 / 2012



The monks clothes proved to be an interesting challenge for this project. From the very beginningI knew that I didn’t want to rely solely on a cloth simulation to take care of the monks clothes.This is because that would bring its own set of problems to deal with, like slow calculation times,interpenetration errors and requiring the endless tweaking of sliders.

Therefore, I wanted to, at the very least, make sure that the rig will allow the animator to pose

the clothes for animation, while not getting too bogged down by the way real cloth would behave.This would provide a simple way to create interesting shapes and silhouettes with just a fewcontrols in the most important places like the sleeves and the skirt area.

The following images show the nal controls around the mesh.

The way in which the controls function had to be built up in layers. First it was necessary to bindthe clothes to the body so that as you pose the character, the clothes move with it. This was donein three different ways. The rst two versions were bound to the same skeleton as the body,one version of which had some extra joints placed at the skirt area so that it could be controlledindependently to the legs. (The other was bound straight to the leg joints)

The third was bound directly to the skin of the body with what’s called a wrap deformer. Thebody geometry essentially acts as a volume with a fall off so that the vertices that make up the

geometry of the clothes are affected by the nearest vertices of the body. This technique workedreally well except for the skirt and the ends of the sleeves.



In order to bring all the best skin binds of the three versions together, they were all mixed into afourth version with the Blendshapes deformer. This way I could paint the areas to be affected by

one version or another, to create one perfect skin bind.

Since there were two versions of the skeleton bind, the rig was made so that you can chosebetween the clothes being affected by the leg joints, or the independent skirt joints, by using a

‘set driven key’ on the two Blendshapes.

The next step was to add the functionality of the additional controls dotted around the mesh so

that they stick to the clothes, but also allow for the re-shaping of the clothes. This is where thingsget really confusing so I shall break this down with a separate example without the clothes.



Take a at surface with a fairly high subdivision level.

The best way I found to re-sculpt the shape using only animation deformers was to use acombination of wire and cluster deformers.

The wire deformer can take any Nurbs curve and make it a source for stretching geometry whenmoved about from its origin.



In order to control the curve which deforms the mesh, I used several clusters, which wereindividually assigned to each of the curves vertices. These basically act as control handles formanipulating the curve.

This works by having two versions of the curve. The base curve, representing the curves origin,and the second curve, being the one that is moved, to deform the mesh.



In order to avoid the cycle error, the Rivets can’t be attached to the same mesh that the wiredeformer is going to be applied to. Luckily all I need to do is create another Blendshape and applythe rivets to the original.

This next diagram better illustrates how this chain of connections avoids the cycle error.

Somehow, I needed to get this functionality built onto the clothes.

The main issue with this is that the clothes are already partially pose-able, and the extra controlswould need to stick to the mesh whilst also deforming the mesh.

The Rivet script provided half of the answer. The Rivet script is by Michael Bazhutkin and is freely

downloadable.

This takes any two parallel edges and constrains a Locator between them with an Aim Constraint,and takes care of both position and orientation which means that I can stick my controls to thedeformed geometry.

However, just parenting the clusters under the rivets is not enough. This would cause a cycle erroras demonstrated in the following diagram, but as you will see, I found a way to avoid this.



So rivets are created around the skirt and sleeves of the skinned clothes. The wire deformer isapplied to the nal clothes, and the wire is controlled by clusters, and the clusters are parentconstrained to the Rivets.

Unfortunately this still won’t work because as the cloth is posed by the joints, the rivets are goingto move the wire, therefore double transformations are going to occur. So the last part of thepuzzle was to take the base wire curve, (which represents the origin of the curve) and createclusters for it and also constrain those clusters to the Rivets.

This way it removes the double transformations. So when you pose the clusters of the main curve,

it is only sculpting the difference between the two curves on top of the starting pose of the clothes.

This nal diagram shows the correct way to connect the nodes.



The following images show how the wires and clusters are working together to make the clothfunction when posing.

Firstly the leg is posed, automatically moving the clothes and their controls.

Then the controls can be re-posed to the desired shape. Notice how the base curve follows thelegs, but remains stationary when the controls are moved. The main wire curve not only followsthe legs, but is also re-shaped by the controls, adding the extra deformation.



To Conclude, here are a selection of images showing the before and after results of animating thecloth.



A Flock of Pixels 2012

UCA University for the Creative Arts

techdocanimclothes2012

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