Augmero V2 Physics Workflow

augmero's physics workflow - Ziva Dynamics for Blender

Last edited: 01/10/2023, version history on GitHub

supporting video documentation - https://www.youtube.com/watch?v=hnPJCRaTDEo

Disclaimer:

This is an experimental workflow. I don't necessarily recommend anybody actually do this.

If you are new to Blender or 3D this post is probably not for you, but bookmark it for later if you're interested

However, if you are looking beyond Blender native physics I hope some of these notes will be useful!

If you found this page and don't know who augmero is, fair warning some links are going to be NSFW. While this workflow can be useful for more general applications, I am using it for NSFW content

Lastly, if you have ideas / improvements let me know! I'll keep this page updated

Tools:

Blender
Maya + Ziva Dynamics plugin

What is Ziva Dynamics?

Ziva Dynamics is a plugin for Maya that specializes in character physics simulation and deformations.
Check out this lion: https://www.youtube.com/watch?v=vsTP6Ldm7Yo
For something more relevant to this post you can take a look at my recent animations (NSFW)
I first found out about this software when I saw tweets from m.tsqn (NSFW), definitely check out what they've made as well

Why not just use Maya?

Many models and shared resources online have armatures and python scripts for Blender with no Maya version, it's not easy to port things to Maya
Most of my experience and workflows (modeling, sculpting, rendering, materials, etc) is in Blender/Cycles, re-learning all of that stuff for Maya is difficult

Surface Deform is better than Mesh Deform

In previous versions of my workflow I used the Mesh Deform modifier, if you're interested in this method historical versions are still accessible via github. Here are some pros and cons comparing Surface Deform to Mesh Deform:

Pros

Much more accurate deformations (no cage, follows the same topology)

For things involving fine details like hand collisions I certainly recommend this over v1

No need to remesh things to make a cage for the main Ziva tissue

I still remesh at times to make things like subtissues

Cons

Less flexible to adjusting with shape keys available after simulation
It can be quite difficult in some cases to bind the surface deform modifier

Note: Adding subdivision or triangulate to the target can help

Overview

If you are new to Ziva/Maya, please watch the elephant tutorial, it goes over most of the basics: https://www.youtube.com/watch?v=QA6C9xzf4f8

These are the general steps for my workflow:

Make an animation with any model in Blender
Make the tissue and bone meshes, export to Maya
Set up and run Ziva physics sim in Maya
Export Ziva physics sim, import to blender
Surface deform original model

Supporting video documentation for this workflow - https://www.youtube.com/watch?v=hnPJCRaTDEo

Step 1 - General set-up

Set up character model with the most general desired shape (likely default pose, shape keys set up for body proportions

You will be able to make adjustments (and animate adjustments) in Ziva as well but a good base gets better results

Any simple animation is fine starting out, even an existing animation you want to add physics to
Pick a frame where the physics simulation will start (I use frame 3) and make sure that your armature stays consistent at that frame.

I recommend keyframing rest pose at the first sim frame for the most consistency and ease of use.

Make vertex group for separating armature vs physics deformation

Exclude more complex parts of the geometry in the physics

Generally, this includes the head, hands, feet, gens.
I include hands as a bone, not part of the tissue cage

We will use this vertex group later for the first two modifiers on the render mesh like this:

Step 2 - Building the exports for Maya, and then exporting them

There are many ways to prepare your tissues and bones for Ziva, if you've got a better way let me know!

Ziva is picky about what it lets you use as a tissue or bone. If you run into issues here's some documentation on what Ziva is looking for zMeshCheck

zBone example: hands

For some context, a zBone in Ziva is part of the simulation that is rigid and can collide with things

Hands aren't incredibly squishy so to save on physics simulation calculations I just make them a bone.

Duplicate the model's mesh and remove all irrelevant vertices
Fill the holes with grid fill
That's it!

Note: If Ziva complains about the mesh when you import it later, check for weird toplogy. Things like fingernails might be messing with it. It's also worth smoothing out the harsh edges near any grid-filled holes

zTissue example: body physics cage

zTissue in Ziva is where squishy happens and there's a lot of settings to play with

Duplicate the model's mesh and remove all irrelevant vertices
Test if the tissue is good by adding a surface deform modifier to the original model, adding the new one as the target of the modifier, and binding. Then test it by adding modifiers to the cage to make sure all the vertices are affected

Note: if surface deform won't bind, adding subdivision or triangulate (or both) modifiers to the target may help

Copy the vertex groups from your original mesh onto your new one using the data transfer modifier

Click on 'Generate Data Layers' first and then apply the modifier
Make sure the two meshes are overlapping, maybe put your armature in rest pose for this section

Clean up deformation artifacts with corrective smooth modifier

Exporting to Maya

It's export time

alembic export - for performance reasons I recommend excluding from view layer collections of anything that's not being exported

This means the checkbox on the collection. Export will be slower if anything else is being calculated by the view layer

For batch exporting alembics, I made a python script, to use it read the documentation in the script. This is much more quick and efficient than doing it through the blender UI

Step 3 - Set up the Ziva sim in Maya and run it

The elephant tutorial can probably teach the basics of Ziva better than me, here's a link again https://www.youtube.com/watch?v=QA6C9xzf4f8

The elephant tutorial is quite similar to what I do, but my alembics are coming from Blender instead

However, there are some specific notes I'd like to share

General Steps

Set your Maya framerate to the same framerate you use in Blender

Maya defaults to 24fps

Import Blender alembic files into Maya
Duplicate it twice (ctrl d), it's going to do multiple things
One version will now be part of the physics sim, make it a zTissue
The other version is now going to become an animated zBone (disable collisons) for attaching the zTissue to

Make a blend shape from the alembic mesh to a duplicate (set envelope to 1)

Make attachments from the zBone to the zTissue

Make sure to set high strength attachments on parts where the cage is next to vertices that won't be part of the final deform, like by the head, wrists, feet, gens. Otherwise the physics sim will travel away from the armature and that's no good
Remember to use vertex select before attaching and then weight paint the attachment to prevent it from affecting parts that don't need to be attached

Optional step: I've been getting improved results by using this alembic as a zRestShape of my zTissue

There is a problem / bug with this but there are workarounds. A quick description of the issue (by my assumptions) is that Ziva is optimized such that if the rest shape hasn't changed a lot it won't update. Since the rest shape is an alembic this can cause some jumping
Workaround: In some cases where this occurs I've had success with an oscillating shape key out of sight used for my zRestShape mesh (doesn't have to be the same as the zBone). The constant changes with this shape key will force Ziva to update. Can also put this shape key on one of the holes that got filled so it never reflects on the original mesh

I have left these steps fairly generic / sparse because the elephant youtube tutorial does such a good job of describing many things in Ziva, and there's a lot of artistic freedom here. This is a really fun part of the flow. There are some more specific Ziva notes I added after Step 5, I'll link them here. They are also in the floating menu

Clothing
Expansion

IMPORTANT NOTE READ THIS: REVISIONS

Revisions are super important for any workflow, here's how to efficiently re-export/re-import your Blender alembics without having to re-do any of the later steps.

Save the Maya scene and then export your Blender alembics, overwriting the existing files.
Use file->open recent and open the same file you currently have open. In reloading the file Maya will get the new animations you exported and you can run your physics simulation again!

(Maya might crash if you try to keep going without re-opening the scene)

Step 4 - Export Ziva physics sim, import to Blender

In Maya, select the mesh you want to export and click Cache -> Alembic Cache -> Export Selection to Alembic (this will play the animation as it's exporting)

In Blender import the file you just exported from Maya

Step 5 - Surface deform the original model in Blender

Simple example of the modifiers at the top of my stack for my render mesh:

That's it! If everything went perfectly the deformations simulated in ziva will now show up on the render mesh

Clothing

Some notes on clothes

For interactive clothing, I add another zTissue but for the clothes in the physics sim

This can have a good result on its own, but to take it a step further software like Marvelous Design can be used as another step afterwards

Expansion

Expansion / inflation, there's a lot of possibilities and potential here

Two main ways I've found to change the proportions on your character with Ziva

zMaterials with rest scale

Pros: Fairly easy to set up
Cons: For animating, you change the 'Rest Scale Envelope' on the Tissue, but this applies to all materials on that Tissue. So if you wanted to increase bust first and then back afterwards on the same Tissue this method won't work

zRestShape

Export one more version of the cage from blender with shape keys over time as alembic! Thanks for the tip @vanasmuttin

I've run into some jankiness with this approach just be warned

Pros: Individual animation over time with envelopes
Cons:

An additional mesh needs to be exported
In some cases to lower artifacting rest shape influence needs to be turned down, however this makes the simulation less accurate the desired shape

Additional Links and Resources

Ziva first party documentation

If you're curious, the Ziva rabbit hole goes much further than the simulations I've been doing. Here's some crazy forum posts I was looking at