Groom Cache in Unreal Engine

 
 
 
Posted by:cortek
Data created:5 July 2022

In version ue4.27, it became possible to import a groom cache from a 3d program.
Unreal Engine has its own groom simulation. Do you plan to add bake groom cache directly in UE?

Are you referring to Exporting Ornatrix hair as Alembic from 3ds Max and then importing it into Unreal Engine? 

Jeordanis Figuereo (Product Designer. EPHERE Inc.)

No, I mean bake realtime hair simulation into the groom cache

So, you are referring to the Animation Cache modifier. This is not supported and I'm not sure how this can be useful, in fact, the hair animation is handled by Unreal Engine itself. Moov Physics is not supported either. Epic recommends using the UE native hair simulation capabilities to accomplish this. Maybe UE have a way to cache the animation. 

How do you want to use this cache? What would your desired workflow be like? How do you handle playback?

Jeordanis Figuereo (Product Designer. EPHERE Inc.)

In Unreal Engine, there is one problem with the MRQ(Movie Render Queue).
If we render video with temperal samples to get a realistic and beautiful motion blur, then the "time" of the world will go crazy. And everything that is considered in real time, whether it be physics or niagara effects, will jitter strangely and behave incorrectly.
To avoid this, it is better to use only baked assets.
At the moment we are filming cinematics in Unreal Engine and we have to do hair simulation in Maya with Ornitrix and then upload to Unreal as Groom Cache.
But this is a very long process when we have a good real-time hair simulation in Unreal Engine. If we can put the Unreal physics in the Groom Cache and use it in the sequencer, that would be a huge time saver.

Sorry, I missed your last comment. 

To be honest I'm just learning UE so I'm not very familiar with this workflow. Ornatrix exports the hair as alembic, after that we don't have any control over it. Since the alembic is imported as a UE native groom, I think it should be possible, once the alembic is inside UE, to use the Unreal physics in the groom, as shown in this video. I just don't know the steps. Maybe you can ask in the UE forums as well. 

Jeordanis Figuereo (Product Designer. EPHERE Inc.)

Actually, this video described the steps. Is this what you are looking for?

Jeordanis Figuereo (Product Designer. EPHERE Inc.)

I think it should be possible, once the alembic is inside UE, to use the Unreal physics in the groom, as shown in this video. I just don't know the steps.
What I'm looking for is a way to INSIDE-UNREAL way to record Unreal physics groom simulation and just replay it during final render.
The problem with real-time simulation during tests in viewport that it looks drastically different from final render and what I'm looking for is more IN-UNREAL control over final result.

In this video you can see "Cache Simulation" bake inside Unreal, like we want :(

https://youtu.be/FBsVp9c7wWY

Ornatrix Alembics will be imported by UE as native hair. After that you can do whatever you want with it. You can add UE simulation and bake it. 

Jeordanis Figuereo (Product Designer. EPHERE Inc.)

Unreal has no tool to bake results of the simulation and I'm asking you to consider to add this bake option as part of Ornatrix Unreal plugin.

I mean about tool like "Animation Cache" in Ornatrix Maya.
Yes, in Unreal Engine we have realtime physics. But we need to bake realtime simulation from viewport.

 You want to add animation to UE Native hair and bake using Ornatrix?

I don't see how this would work. Ornatrix hair and UE Native hair are different things. Once you convert Ornatrix hair to UE Native, unreal is responsible for the hair. Ornatrix has no access to it. 

To clarify, Ornatrix is intended to Create and Edit UE Native hair. It is not intended for hair animation. You can only add animation to the hair if you convert it to UE Native hair.

The feature that you need should be added to UE itself. 

Jeordanis Figuereo (Product Designer. EPHERE Inc.)

Did a resolution for baking the groom physics appear anywhere. Regardless of Ornatrix, have terrible problem with MRQ and native groom physics going wild during render at high quality.

The problem is that to add dynamics to the hair you need to convert the hair to UE Native hair, after that Ornatrix doesn't have any control over it. This should be solved in Unreal Engine side. In other words, this feature needs to be implemented in UE, by Epic.   

Jeordanis Figuereo (Product Designer. EPHERE Inc.)