Making Blubber Jiggle

A tutorial by Chris Browne <pseudopod_prod@yahoo.ca>



 

Fig.1

This is a tutorial on how to rig a fat blubbery character in such a way that when s/he moves, their blubber flops around like real flab without having to key or shape animate the fatness. This technique can also be applied to the breasts of a female or transsexual character.

The following tutorial is for Softimage XSI users who have a good understanding of enveloping, character rigging and working with constraints for Inverse Kinematics.

 

1.Start by placing the appropriate bones in your character. Donít worry about anything but the character's regular bone setup at this point.

 Fig2

2.After the bones are in place, observe the areas in which the fatty parts of the body extend (or hang) furthest away from the character's bones, where there would be the most overlapping movement.

Fig3

*Like most overweight people, the main areas are in the abdomen, chest, love handles, under the biceps, and sometimes under the chin. This tutorial will focus on the first three areas, however the technique can easily be applied to all five.

 

3.Make your Mesh Object unselectable. Starting with the gut, find the closest corresponding bone. Create two implicit objects, scale them down and arrange them from the bone to the stomach bone.

Fig.4

4.Parent the implicit object closest to the bone (make the implicit object the child of the bone). Select "Comp" as in "compensate" under the constrain tab. Then position constrain the other implicit object to the one parented to the bone. (Observe the diagram below)

 

Fig.5

5.Select the implicit object that is position constrained. In the explorer, open up the object's properties and double click (open) the Position Constrain editor.

Fig.6

6.With the Position Constrain editor open, under Coupling select SOFT. Decrease the blend weight value.

Decreasing the blend weight value causes the delayed or overlapping movement in the constrained object. The amount that this is set at depends on two criteria; how much overlapping movement will be necessary with the amount of blubber the character has, and how fast the character is moving. This is a setting that can be changed at any time whether it is after the character is enveloped, and or after the character is animated. This is also a setting that can be changed and keyed throughout an animation to get the desired result. This feature can be keyed by selecting the green dot beside the slider. Since it is a variable that depends on a certain situation, it is best to eyeball it, perhaps after there is animation.

In this scene, the character is walking at an average marching pace; therefore, the settings for the "blend weight" will be best set according to that. Set "Blend Weight" to 0.36. Don't worry about the other values in the editor yet. Leave them at the default for now.

Fig.7

7.The Love Handles work pretty much the same way as the gut, only they are arranged along the side of the stomach bone. (The diagram below has the previous implicit objects hidden for viewing purposes)

Fig.8

8.Repeat steps 5 and 6 for the two constrained implicit objects. Set the blend weight to 0.7.

Now that the stomach area is complete it is time to work on the chest.

9. Arrange three sets of implicit objects on each side of the chest. (Use diagram for reference)

Fig.9

Be sure to position the top implicit objects at the shoulders. (Where the collar bone meets the bicep)

10. Parent the top (shoulder) implicit objects to their corresponding bicep bone.

11. Position Constrain (with Comp selected) the next implicit object to the one that was parented. Set the blend weight to 0.95 and set Coupling to SOFT.

12. Position Constrain the implicit object after that to the one above. Set the blend weight to 0.9 and switch Coupling to SOFT. (Make sure the settings are the same for each side of the chest).

13. Select all implicit objects that have been position constrained (and have not been parented to anything) and Parent them to the top null of the skeleton hierarchy.

14. Make sure you name all of the fatty control objects as well with the bones. This will make weighting easier.

15. Make a group of all bones and fatty control objects and label the group as "Deformers".

16. Select your mesh object and envelope it to the Deformers.

 

17. Weight your character smoothly throughout the areas where the fatty control objects are so that there is no unnecessary creasing when they move around. The "apply smooth" tool in the weight editor is useful for this.

18. After the character is properly weighted Group all of the fatty control objects and make them unselectable. Do not hide them, if they are hidden they will not work.

19. Animate the character. As the character moves around the fatty control objects might move either to freely so it appears as though they have a life of their own, or not enough to detect them. Experiment with the "Blend Weight" slider of the Position Constrain editor to find the best fit. When the movement is subtle yet noticeable, it looks the most convincing.

20. If the fatty control objects tend to stick out or sink into the mesh (aside from the blend weight), try adjusting the sliders under "Constraining Object" in the Position Constrain property menu. In the diagram below, the gut is set at -0.2 to get the fit for the particular movement that the character is in. This function is fully animatable and keyable aswell.

Fig.10

 

21. One last thing to note is that the constraining objects are live. This means that as the character is moved they work, rather than only when you set keys. This may mean that ten or so buffer frames might be required at the beginning of an animation; however, they most likely wont need to be rendered.

Hopefully this will be helpful in creating more convincing and life like animated characters

This tutorial was created by Chris Browne and was provided by Pseudopod Productions.

Chris Browne is an Animator, Modellor and Visual Effects artist located in Vancouver Canada. He recently completed his second short CG animated film titled BRAND "X" Mas currently submitted in the film festival market. Aside from independent films Chris also does freelance work in the field of computer animation and visual effects, including work on MGM's Sci Fi series STARGATE SG1.

To view information on Chris Browne's first independent animated film please select the following link:

http://www.bigfilmshorts.com/catalog/target.asp?FilmNumber=S%2D0305

For more information email:

pseudopod_prod@yahoo.ca