Maintaining mesh volume for squash and stretch

00:03

What we have now is a torso which stretches which is good,

00:07

but it doesn't maintain its volume.

00:10

What I mean by this is it doesn't get thinner,

00:13

the more it stretches or thicker when it squashes,

00:16

let's add that functionality in next.

00:19

And it's pretty straightforward. Now, we have the main stretching network set up.

00:24

All we need is another multiply divide node

00:27

call this spine volume multi.

00:32

This time we need the operation to be set to power.

00:36

What this will do is take the input one X value and then

00:40

multiply it by itself the number of times in input two X.

00:45

So if input one X was two

00:47

and input two X was two,

00:50

it would be two times two

00:53

set, input two X to minus one because we want the scale value to get smaller,

00:58

the more the torso

00:59

stretches

01:01

now connect out color R from the condition node to input one X.

01:08

Remember this is the main scale value being output

01:11

plus it's being controlled by the condition node.

01:14

Let's reuse the IK blend colors node. Now,

01:18

so we can again control the influence depending on

01:21

whether the animator is using the IK or FK spine

01:25

connect output X from the volume multiply divide node to color two G.

01:32

And now we connect this to the other scale attributes on the joints.

01:37

Actually let's use a connection editor.

01:40

So load the blend cos

01:42

node into the left side

01:44

and the bind joints into the right.

01:47

We only need these because they influence the model.

01:51

So we need output G

01:53

and this time connect to scale X and scale Y on each joint,

01:59

you can see they are now connected up here.

02:03

Now, as we pull the shoulder, control

02:05

the torso changes shape as it stretches

02:08

and when it squashes,

02:10

it's also ignored when switching to FK.

02:14

So the spine is done.