Shading Rig: Dynamic Art-directable Stylised Shading for 3D Characters

Despite the popularity of three-dimensional (3D) animation techniques, the style of 2D cel animation is seeing increased use in games and interactive applications. However, conventional 3D toon shading frequently requires manual editing to clean up undesired shadows or add stylistic details based on art direction. This editing is impractical for the frame-by-frame editing in cartoon feature film post-production. For interactive stylised media and games, post-production is unavailable due to real-time constraints, so artdirection must be preserved automatically. For these reasons, artists often resort to mesh and texture edits to mitigate undesired shadows typical of toon shaders. Such edits allow real-time rendering but are limited in resolution, animation quality and lack detail control for stylised shadow design. In our framework, artists build a "shading rig," a collection of these edits, that allows artists to animate toon shading. Artists pre-animate the shading rig under changing lighting, to dynamically preserve artistic intent in a live application, without manual intervention. We show our method preserves continuous motion and shape interpolation, with fewer keyframes than previous work. Our shading shape interpolation is computationally cheaper than state-of-the-art image interpolation techniques. We achieve these improvements while preserving vector quality rendering, without resorting either to high texture resolution or mesh density.