Preparing Realistic Wolf Skin and Textures with Houdini & Mari

Sasha Hequet showed us the workflow behind the ongoing Wolf project, talked about sculpting in ZBrush, and shared her node setup in Houdini.

Introduction

Hi! I’m Sasha Hequet, a CG Surface and Groom Artist. I create realistic or stylized textures, hair, and lookdev for characters, animals, and creatures. I love to experiment and learn new things.

I can work on something realistic like this very project or something stylized like Leo, the animated feature film I worked on at Animal Logic the past year. I choose to work in surfacing and grooming because I think it is a perfect balance between artistry and technical. 

This year, I wanted to sculpt a specific wolf I saw in a sanctuary in Banff to learn more about animal anatomy in detail. I've always been interested in painting and photography, so it was great to have the chance to take pictures for my references. There is accessible data on wolves' and dogs' anatomy, so it was easier to analyze and reproduce for a first big project like this.

The goal is for this asset to look photoreal and to make it production-ready to do a short video with it. Let’s begin!

The Wolf Project

Because I wanted to learn anatomy, I sculpted everything from scratch. So I needed a solid reference board; I used PureRef for that. It is filled with pictures of wolves I took and veterinarian content, mainly from the ENVA veterinarian school in Paris.

I followed Pablo Munoz Gomez's tips for PureRef and inserted segments on my board. I marked down different types of lengths and tried to find similarities to help with the proportions of my model.

I also like to import my drawings to PureRef, either to not lose track of a thought I have or to decompose the images into what I see. Sometimes drawing on top of pictures can be useful.

Sculpting

The first thing I did was rearrange the layout so everything I needed was accessible to me. For example, I made a custom shelf that regroups the things I use most, I bring it to the screen with the “Ctrl+R” hotkey.

I also modified the StartupHotkeys to select the brushes quicker, e.g., the Clay Buildup brush is under C. ZBrushGuides is a very resourceful website with a lot of free organic brushes.

I started the skin in ZBrush with simple volumes and shapes. I tried to stay on the lowest subdivision level as long as I could, it is much easier to change proportions. When I felt like I was close to my reference, I put the PureRef file on top of what I was modeling
and reduced the global opacity in the settings to compare my model to my refs more accurately.

You can also enable the "always on top" and "transparent to mouse" modes if you want to modify your model underneath your reference.

I modeled and did the UVs of each bone of the skeleton in Maya. Then I imported my skeleton OBJ file in ZBrush to make it fit underneath the skin.

Once I got everything ready in ZBrush, I exported what I sculpted to Maya to do the retopology and UV mapping of the skin mesh.

I made two UV sets for the skin: one for texturing and one for the groom. It allows me to paint the groom masks directly in the UV view of Houdini.

These are the resources that I found useful for the sculpt part:

Texturing

I did the texturing in Mari. I love to paint, so this one was fun!

You can see the base color and roughness here.

Houdini

The Alembic file I exported from Maya allows me to keep the groups and will be useful in Houdini.

There are several ways of working on such a big project in Houdini, my advice would be to find what’s best for you. I hope you’ll be inspired by how I did it.

My first Geometry node (Geo Lookdev) controls which mesh and version I am using. I edited the parameter interface of this Geometry node, so it only displays the two files to change. 

Inside it, I have my Alembic node and use the groups I created previously in Maya to separate my mesh by material. I put a Null node at the end of each material selection for naming.

Then in my lookdev subnet, I created a Geometry node for each material with an object merge to call the material selection I did earlier and assign the material. Here is an example for the skin:

Each Geometry node is here to be able to control the subdivision level, displacement, or other Arnold parameters individually.

The Matnet (in the blue backdrop) is where I worked on the materials. Inside of it, I created an Arnold material builder and then created my Standard Surface material.

I used XYZ Textures for the pores of the skin. To render everything, I created an Arnold node in the “out” network. I have two for the different settings I use: one for the still images with a little bit more sampling than the second one, for my batch render.

I also created an environment setup subnet with all of my cameras, light rig, and environment geometries such as grey balls, a color checker for ACEScg, and forest ground.

My HDRIs are linked to the camera animation.

Conclusion

My main focus in this big project was quality and finding a new workflow. I took my time to make everything organized and enjoyed the process. 

I love using Houdini when I am working on all aspects. Once it is set up, you can really speed up your workflow by avoiding doing the same thing all over again when an update comes.

It was so helpful to ask for feedback and I am very grateful for Nicolas Morel's precious advice on the sculpt and Clement Feuillet's texture knowledge. 

Thanks a lot, 80 Level, for publishing the article and I hope that I have inspired and helped you all!

Stay tuned for the grooming part and good luck on your future projects!

Sasha Hequet, Surface & Grooming Artist

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