User Guide > Characters > Rigging   

Muscle Deformations with Inflate

The Inflate tool can be used when you want a character's skin surface to look like it is reacting to underlying muscles and bones. This tool lets you push your skin geometry using other deforming surfaces.

For this lesson, you will start with an animated arm with bones and muscles set up for the upper arm. Using a simple piece of geometry as a starting point, you will inflate its surface to match the deforming muscles and the animating bones.

Load Start File


1. Preview the Muscles

Scrub in the timeline to watch the animation of the arm bending and the muscles deforming. The goal is to transfer the deformations found in the muscles into the character's skin surface.


2. Display the Parts

Select the skin object and press i to go into the object. Select View > See All Objects from the Pane menu to turn this option Off. Set the display flag for the skinmass SOP and the template flag for the toolgroup SOP.

The skinmass chain is made up of a line that is deforming with the bone. This line is then turned into a simple surface using a custom tool that sweeps a circle along the line then caps one end. You can select skinmass and press i if you want to see how it is built. Be sure to press u to go back up when you are finished. There is also a group SOP assigned to the line to help prepare it for the Inflate.

The upper_arm chain includes an Object Merge SOP that brings together the bones and muscles from other objects. Again a group SOP is used to name these parts for use in the Inflate.


3. Merge the Inflation tools

In the Network pane, press tab > Merge and place the tile just under the toolgroup SOP. Wire the output of the toolgroup SOP and the output of the deform SOP into the input of the merge SOP. This will make it easier to pipe these parts into the Inflate.


4. Create the Inflate SOP

In the Network pane, press tab > Inflate and place the tile below the merge SOP. Wire the output of the skinmass SOP into the first input of the new inflate SOP and the output of the merge SOP into the second input of the new inflate SOP.

Turn on the display flag for the inflate SOP. This initially results in an error because the groups have not yet been referenced.

Select the inflate SOP and in the Parameter pane, set the Tool Group to toolgroup and the Center Prim Group to centergroup. This references the group names from the two networks and the Inflate error is fixed. Next, turn on the Inflate to Farthest checkbox and the Inflate can be seen pushing the skinmass surface out to the muscles and bones.


5. Adjust the Skin thickness

Next, select the skinmass SOP and in the Parameter pane, adjust the Fat parameter. This loosens or tightens the skin over the muscles.


6. Preview the Results

Press u to go up to Object level and create a Flipbook animation preview to see the muscles deforming the new skin surface from below.


Conclusion

The Inflate tool lets you define a character's skin using the muscles themselves. Rather than put the time and effort into modeling the skin, the time would now go into the creation of realistic bones and muscles that will create the skin procedurally using the Inflate tool.