Shading

Shading is the process that computes the color and brightness of a surface in a 3D scene based on lights, material properties, and viewer direction. It encompasses algorithms and shader programs that determine how light is reflected (diffuse, specular) and how attributes like glossiness, roughness, and shading gradients appear. Shading can be performed at different granularities (per-face, per-vertex, per-pixel) and is central both to artistic styles (e.g., toon shading) and to photorealism (e.g., PBR — Physically Based Rendering).

Imagine you're building an AR app that places a metal vase on a table. With simple Gouraud shading (per-vertex), you get smooth color transitions but specular highlights can be inaccurate or missing for small shiny details. Using Phong or per-pixel PBR shading with a normal map and a correct BRDF produces sharp, realistic highlights and reflections that make the vase look convincing; note that per-pixel computations and high-resolution normal maps are more expensive, so on mobile XR devices you often need optimizations like LODs, baked lighting, or texture atlases.