Shrinkwrap - XSI

A geometry deforming process will simulate skin sliding over a muscle and can simulate wrinkles as they bulge.

Working like cling film it functions the same as cloth and is used used as an alternative.

Setup as well as the calculation time required is quite high (depending on the density and complexity of your mesh). There are a few tried and tested methods to create skin slide, I will attempt to demonstrate the method of using the shrinkwrap tool to gain slide over deforming objects.

Using a simple system replicating an arm, a two bone skeletal chain can be used. Projects the points of a “wrapper” object onto the surface of a “target” object, either toward the target’s
center, toward an inner object, or along an axis. Points that do not “hit” the target according to the chosen projection are not moved [xsi help]

Any object surfaces, surface meshes, polygon meshes, and curves onto other like objects.can be skinned using shrinkwrap.maintaining the modeling relation the target can be transformed or deformed after the deformation, the
shape of the wrapper is altered accordingly

Deformation happens in realtime, if there is a lot happening on a dense mesh performance takes a hit, a button can be made to mute the shrinkwrap operators whilst animating to speed the process.

Issues and bugs appear labelled in the xsi documentation making it an unstable process. One example i discovered on this set up was the translation of the centre target object. It needs to stay inside of the object NEEDS to be inside the mesh its deforming, or there will be "un-predicted" results. Muscles jump to an extreme positions. The reducing the amplitude slider, can rectify the problem.

The tool is native to xsi therefore clearly documented and despite its simplisity and lack contols. Shrinkwrapt has been proved to be stable enough to play small roles in production, an example of this can be seen used to stick the bug to the fairy in Pans labryinth.

 

created by lawrence elliott MA 3D Bournemouth University 2008