Sculpting and Texturing a Stylized Skull Axe

Introduction

My name is Kristopher Vita, I am a Character Artist for Video Games from the Philippines. I studied at the Academy of Art University back in 2008-2011 to get my Master's of Fine Arts in Animation and Visual Effects with a focus on 3D Modeling.

I started working back in 2011 at Floathybrid Entertainment in San Francisco as a 3D art intern. Then from 2012 to 2015, I worked at nWay in San Francisco as a 3D artist to contribute Character and Weapon assets for Chronoblade. I worked at Section Studios in Los Angeles in 2015-2018 to contribute 3D assets for titles like Eclipse Edge of Light, Outer Wilds, Misbits, and Rival Crimson X Chaos.

Currently, I am leading a team at System Studios in the Philippines, contributing to titles I am not at liberty to tell, for film, mobile games, next-generation console, and PC. We have contributed character and hard-surface assets for the short film "Drift" by Parallax Studios as well.

My primary role is to create 3D assets, character, and hard-surface to serve as a visual benchmark while training my team to be able to do the same. Shout-out to my teammate Eric Lascona for training the team as well. We have trained guys from the miniature and toy industry who now have a great understanding of the complete game art pipeline.

Skull Axe: Concept

The Skull Axe concept was made by Duy Nguyen. With his permission, I created the 3D asset using his concept and recorded the entire process of creation.

The goal for this asset was self-improvement! For each personal artwork, we have an artistic responsibility to always push beyond what we are currently accustomed to. The challenge was the fact that these types of assets are generally hand-painted and diffuse-only. I asked myself what I can do to mix and balance the color principles in hand-painting with the PBR principles in current and next-gen gaming. This was also submitted as an entry to Artstation's Create Your Destiny Marketplace Challenge.

It was heavily inspired by the Darksiders series so I had a bunch of references that hit that style on my reference board. I used either Kuadro or Pureref for reference.

Sculpting

The blockout was quickly done in Maya, the same principles can be applied to any core modeling package of your choice though. The emphasis is on getting the silhouette of the concept 1:1 and then the main forms and plane breaks can be done in ZBrush or any digital sculpting package of your choice.

For the blockout and high polygon stage, I have a rule that if it's separate in real life, it should be separated as a subtool. This way, I was able to make full use of efficient polygon subdivisions in ZBrush. Also while the concept is heavily stylized, we still have to imagine how it would look like and how forms would intersect as if it were physical in real life.

(I should have named my subtools though or grouped them in folders! If you are in production, name your subtools as if another person would take over the asset).

Another tip that I would like to give is the following: after the blockout is set in ZBrush, it is very important for me to establish a visual anchor for the piece. Make one subtool look really good and then have the other subtools follow that same sculpt fidelity, one subtool at a time. For this instance, I set my visual anchor to be the skull area.

My brush set is pretty simple: DamStandard, ClayBuildup, TrimDynamic, Hpolish, and Move Brush, all set into hotkeys. I avoid using custom brushes made by other artists because I think you lose a lot of your artistic development and identity in your personal work. I do have to add that if this is professional work, everyone should definitely be using the same base meshes, brushes, and techniques for consistency. 

Here are some rules on establishing sculpted edges, forms, and nice plane breaks:

• Vary up your edge damage, not everything has to be soft, sharp, or chiseled. Instead, focus and use edges to direct your eye towards the focal point, have edges sharper where that area is and have softer edges on less interesting areas. Edge control is also applicable in sculpting, not only in painting!
• Have varying depth on your recessed forms.
• Focus detail where forms intersect. I try to put cracks and detail to where the teeth hit the base and where the blade meets the skull.
• Apply storytelling to your sculpt. Where the axe is getting hit all the time? Put damage in there!
• Use a ton of references! Have a reference sheet for damaged metal, skulls, weapons, anything that can help you, the internet is your friend.
• Each subtool should look good on its own.

Retopology and UVs

The retopology is done in 3D Coat, which in my opinion is the best middleware 3D core package out there. With that being said the retopology principles are achievable with whatever core modeling package is out there.

I take into account maximum silhouette and sensible polygon count in current and next-generation games. I try to establish the highest polygon density into the focal point of the asset. With this in mind, I am able to decide which details will be handled by the normal map or by geometry. 

The UVs are pretty straightforward, nobody loves them but it's a necessary production skill. Mirror along the Z-axis and use the standard unfold tools in Maya. Cut, Split UV, and Harden edges wherever there are 90 degrees harsh angles. 

I used 3D Coat here as well. I used the layout tool so my UVs have uniform and maximum texel density. Alternatively, the layout function in Maya works too!

Baking

To prepare my model for texturing, I exported a decimated model of the axe from ZBrush into Marmoset Toolbag to transfer my high-resolution detail to my low poly asset. They have a pretty extensive write up on that process here.

I love Marmoset Toolbag, Being able to see in 3D the interactive cages and real-time spot-fixing is a game-changer. I try my best to make sure my bakes are extra clean, artifact-free, and need no fix in Photoshop. The maps that we get from Marmoset Toolbag – normal, object space, position, ambient occlusion, concavity, convexity, and thickness – are going to dictate the quality of the generators that we get from Substance Painter.

Texturing and Materials

To choose the color palette for the model, color picking from the concept is a great starting point. However, it doesn't always pan out great when hit by lighting, so I cross-reference it with measured PBR charts, but not that much, so there is a balancing act to be made. One thing that I established early on was to make sure that the hues of a material type are all different in the "light, mid-tone, and occluded areas" while at the same time making sure I didn't paint in lighting information such shadows and ambient occlusion. We have normal mapping and dynamic lighting, so shadows should be handled by that.

The tools that I use in Substance are pretty simple. I just use fills and simple smart masks, AO masks that I blend in with multiple custom grunges. I try to mix in the strengths of Substance Painter's procedurals and do a detail hand-painted pass. I also use the baked lighting filter, AO fill in combination with gradient filter in Substance Painter to map out the local colors of each material.

Metalness is pretty straightforward, White for metals and Black for non-metals, some transitional dirt is okay but I try to clamp them to avoid the halo effect. 

For the roughness, if the sculpt of the surface is good and has detail, then having a flat value should work just fine. I try to avoid having random clouds, grunges, and dirt in the roughness layer that doesn't match the surface sculpt, it tends to be noisy when hit by lighting and does not help when directing the eye.

For this project, I've established a bunch of rules for myself when authoring the materials. Mainly:

• The asset should look good in all lighting conditions.
• The textures should be PBR validated as much as possible, meaning, albedo cannot go beyond too dark or too white. Metalness is either pure white or black (read PBR Guide from Substance Academy).
• The local colors of each material type should reflect the concept and still have a painterly feel but the sculpted forms should drive most of it (no painted cracks!).
• Composition and directing the eye > PBR correctness

I've found that having correct base values for each material in the albedo, roughness, and metallic helps a lot in being PBR correct. 

Then for stylization, we can adjust the color as if it were a hand-painted piece but only shift the color and saturation, less the value. Because these types of concepts are generally created as a hand-painted asset, I try to blend in some of those principles when creating the asset as a next-gen piece. When I do paint in "shadows and AO", I make sure I paint in occluded dirt and sharp dirt instead so it is still logical. When I do paint in "highlight areas and areas of saturation", it becomes equivalent to either logical surface wear, edgewear, or hue shifts. I always make sure that I do more Hue-Saturation shifts rather than Value Shifts. 

I notice that when most stylized assets are created, it sometimes doesn't work with multiple lighting scenarios because a lot of the albedo and lighting information is baked in. So to solve that I make sure I switch HDRIs in Substance Painter and make sure it looks good in every lighting scenario.

Another thing that I want to emphasize is composition, I want to make sure the material difference in my asset supports and directs the viewer's eye towards the Skull area. Hue, Saturation, Value, Detail Intensity, Negative Space, Emissives, and Material difference are all tools that I can use to direct the viewer's eye towards the focal point of the asset which is the Skull. I hope I was successful in that!

Rendering

My rendering setup is straightforward in Marmoset Toolbag. I darken the main sky and create child lights from the HDRI to create a simple three-point lighting setup. I have a key, fill, and rim. I want to make sure that composition-wise, the viewer looks at the skull part of the axe.

The lights in the eyes are controlled via painted emissive map+bloom post-processing to have a screen-space effect.

For the mouth to be lit, there are two points lights in there, one bright orange with high intensity and low distance, and the other is bright red with medium intensity and medium distance. I tried painting in emissive maps in the mouth but it started to look spray-painted or like a sticker.

My post-production setting is straightforward as well. I cranked the GI settings to have ludicrous shadows, max samples, and eyeballed the bounce lighting. I have the standard bloom, grain, and vignette settings that enhance my piece but not overdo it. I adjusted the exposure and played around with the contrast. I tried the extreme ones where there are a universal bloom and crazy lens flare all over, then I started dialing them back.

I actually have multiple post-production settings in each of my renders. Play around and try in relation to your asset. What works for you may not work for me.

To choose the right angles, I imagine how it would be used in-game and look like in multiple environments, on the cover of a game maybe or on the select screen.

Kristopher Vita, Character Artist

Interview conducted by Arti Sergeev