NormalAttribute

NormalAttribute is a data attribute used in 3D graphics and game engines to store normal vectors for vertices or faces. Each element represents a normal direction at a vertex (or for a polygon in flat shading), typically as a 3-component vector (x, y, z). The attribute is used in lighting calculations to determine how light interacts with a surface, influencing shading models such as Lambertian, Phong, or physically based rendering (PBR).

Storage and formats commonly involve three floating-point values per vertex, often normalized to unit length. Some pipelines pack normals into smaller formats for memory efficiency, such as 16-bit or 8-bit components. In standard file formats and APIs, normals are exposed as a per-vertex attribute named in different conventions (for example, a NORMAL attribute in glTF or a vn entry in OBJ).

Shading effects rely on NormalAttribute to compute illumination. Per-vertex normals enable smooth shading by averaging adjacent face normals, while per-face normals yield flat shading with a hard edge between faces. The choice affects how subtle lighting variations are perceived on curved surfaces.

Transformation considerations are important: when a mesh is transformed by a model matrix, normals must be transformed differently from positions. The correct operation is to apply the inverse-transpose of the 3×3 portion of the model matrix, followed by normalization. This preserves correct lighting under non-uniform scaling or shearing.

In practice, NormalAttribute is exposed as a vertex attribute in geometry data, often as a 3-component Float32Array per vertex, and consumed by vertex and fragment shaders for lighting calculations. Related concepts include vertex normals, normal maps, and tangent spaces.