Learning The NPR (Non Photo-Realistic Rendering) Workflow

Hi, all. Today's post is going to focus on what I learned when applying advanced workflows to achieve a NPR , or Non Photo-Realistic Rendering, style. In particular, I am going to focus on the creation of a player model for my main character in my in-development game, Lying Saturday. The creation of the character took a couple of months, as I jumped through the character art pipeline, and some specific things that are exclusive to how NPR artists achieve specific looks. This would be fundementally different from my experience with realism and PBR, and it would open my eyes to a completely different workflow.

What is NPR?

In the Game Art pipeline, one will often come across the term PBR, or Physically Based Rendering. This is a methodology where materials and lighting are represented like it would be in the real world. By having a system which allows us to easily describe qualities and how they interact with light, game artists are able to create convincing realistic results which allow us to immerse ourselves within the realm of a game.

NPR or Non-Photorealistic Rendering is the antithesis of this methodology, where the rendering and its qualities do not match how they would within a real life medium. In doing so, and by breaking convention, game artists are able to create expressive styles and aesthetics without any bearing on how realistic something looks.

This means that shadows can look how an artist likes, or a material can have stylized celshading reminiscent of anime or cartoon shading.

My original concept art for the character 'Mycka'.

Goal : Creating a Character

My goal for the past few months was this :

Create a functional playable character which used the Unreal Mannequin as a skeleton base, and make it compatible with a stylized NPR shading model I had in Unreal.

This endeavor would take significantly longer than planned. Along the road, there were a lot of NPR specific techniques to learn that I was never exposed to. And so half of my time spent on the character would be approaching 3D art differently than I was used to, and breaking rules within PBR workflow at its most fundamental level.

Breaking The Rules : UVs

One of the new techniques I learned was the utilization of UVs to create crisp and un-aliased lines when applying a texture map. This is accomplished through 'squarifying' the UVs so that the pixels of a texture map align straight. This technique was popularized by the character artists at Arc System Works, the creators of popular fighting games like Guilty Gear and Granblue Fantasy Versus.

Here, you can see that any place where I want an outline. I straighten the edges of the UVs. This leaves me with a ton of strips so that I can have a straight black line in the base color texture map.

You can see any place that an outline is needed, I keep the UV Shell edge relatively straight and avoid diagonal lines as much as possible.

Note the nice clean outlines. No aliasing or jagginess due to squarifying the UVs.

Breaking The Rules : Topology

Another thing that I had to adjust to was the usage of topology to achieve better looking shadows for the model. By editing both face normals, and topology, an NPR artist is able to achieve more controlled results for every single angle that a light can hit their model. However, by doing this, they break some pretty popular rules for 3D artists.

The first rule they break is that, when modelling a living thing, the edge flow and topology should generally follow the anatomy and muscle structure of the thing you are modelling. Some NPR artists throw this rule out the window and instead have topology that is more suited for how they want their model lit. You'll see in the images below, I have clusters of weird looking polygons and edges which are intentional and create a specific shadow shape when hit at a certain angle.

Original Topology

The New 'Cursed' Topology

Breaking The Rules : Normal Editing

One of the more challenging but rewarding parts of learning the NPR workflow, was learning Normal editing. This is a very crucial step in order to achieve more stylized lighting and shadow for a model, and there is a lot of trial and error when it comes to editing your normals to look good under every single angle and lighting scenario.

Artist : Andrew Lester

A lot of anime tends to have a little triangle shape under the eye when a face is lit from the sides.

Sonny Boy (2021)

I also wanted good exaggerated lighting for the sides of the face when lit from the left or right.

Sonny Boy (2021)

Anime has some hard shadow shapes that aren't achievable without first having the topology and proper normal edits.

Editing normals is a daunting process, and it looks overwhelming at first.

The light blue lines indicate the zones where I want the shadow to step.

I got the little triangle under the eye by editing the normal for the section.

The end product after all of my edits to the face normals. You can see a stark difference between the auto generated mesh normals, and the ones I edited to achieve a more stylized look.

The Cherry On Top : VFX and Custom Shading Model

Along with all the previous steps to achieve a more stylized look, I also feel that shaders and VFX also added to the identity and aesthetic. So doing what I do best, I put together some effects for the movement of my character and used my Custom Shading Model to create a shader which brought the visuals more to life.

You can find more about my Custom Shading Model here.

My Custom Shading Model allows me to change the way shadows look. In this shader, I use it to change the tint of shadows which can even be changed at runtime through a variable.

A lot of my stylized VFX tend to use Distance Field texture masks since I like the way they look and can be used to animate.

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