Rigging - How do you preserve the belly volume of a chubby character?

Question

I am facing an unusual problem while rigging an obese/fat character. Please find the screenshots (here the term ‘obese’ is used to point out that the issue is only arising for this kind of character shape only and don’t consider this otherwise please).

When the character is seated, its belly portion is getting into its body. I did plenty of rigging with many other normal characters, however, did not find this kind of unusual issue.

I am also providing a google drive link to the Blend file. https://drive.google.com/file/d/1LH5WHLuImztqtofeSi2AK7oXZXncrwuq/view?usp=sharing

Answer 1

For this big guy, I would add an extra bone that preserves the volume of his impressive belly.

This works in a similar way to the chest bones. You have probably removed these bones but in fact, I would restore them so that this male character can also take a deep breath, stick out his chest and pull in his belly to impress women. (It's a bit hard to do this with only the belly bone).

^{Scale and move the new belly bone to control the abdominal fat.}

How to Add the Belly Bone to the Metarig

Just copy the second spine bone (spine.001), rotate it and align it to the belly. Make sure it's on the bone layer that you want (1) and the parent relationship is correct (2). You need to be in Edit mode to change this setting.

In Pose mode, make sure you select the Rigify Type basic.super_copy (3) and, last but not least, use the Options of it to generate a control bone for it (4). Then re-generate the animation rig with the Rigify button.

^{Customization of the Metarig}

The control bone for the belly (yellow circle) might be hidden inside the character. In this case, you can adjust the Viewport Display > Translation Y value of this bone to move it outside.

^{Adjusting the position of the control bone}

How to Fix the Hole in Crotch Area

The shirt and the pants of this character are loose mesh parts and not connected. The calculation of the Automatic Weights does not work very well in this case. When the character sits down, a large hole opens in the crotch area.

To fix this, I've duplicated the model, remeshed it, and bound the dummy to the rig with Automatic Weights. Finally, I've transferred the weights back to the original model. For details, have a look at this question & answer: Armature with automatic weights using Rigify failed