This stage was crucial for the project, as it would determine the overall look and feel of the film. While exploring different visual styles, I came across a few tutorials on cel shading in Unreal Engine. After experimenting with several combinations, I ended up building a custom cel shader that runs entirely through the Post Process Volume. Alongside this, I also created a custom fog material to support the stylised lighting.
Cel Shading : Post process Volume
The cel shader works by separating the RGB channels of the scene and then multiplying them back together using custom parameters to form distinct light bands. I added separate controls for each band:
- Band A, B, C, D controls: Adjust the spacing between each shade band.
- Light A, B, C, D controls: Adjust the brightness and intensity of each band individually.
There’s also a global tint section that lets me shift the overall colour of the highlights and shadows, interpolating between the darkest and lightest shade bands. This became especially useful later when switching between the warm desert environment and the cooler underground cave.
Because cel shading can override coloured lighting, I added a section that brings the light colour back on top of the shading. Without this, coloured lights would be lost in the effect. I also included an exclusion section, allowing me to remove specific meshes or particle systems from the cel shading if needed, which gave me more flexibility during production.
Having everything parameter-based made it easy to test different colour palettes and lighting combinations for both the exterior desert scene and the underground environment.
Volumetric Fog : Post process Volume
For the fog, I created a simple but effective material using a depth fade node and a short sequence of mathematical operations. This resulted in a three-colour fog with height and opacity controls.
In the underground scenes, I inverted the height logic so that the fog started low at the water’s surface and became denser towards the cave ceiling. This made the underground chamber feel deeper, darker, and more mysterious.
In the exterior scenes, I used this to create multi-coloured atmospheric fog, which enhanced the stylisation and helped push the steampunk-sci-fi tone further.
Final result
With both the cel shader and fog material complete, I now have a reusable stylised shading setup that I can plug into future projects whenever I want to achieve a similar look. This stage ended up becoming a defining part of the film’s visual identity.