tangentnormal

Tangentnormal refers to a normal vector expressed in tangent space, typically stored in a tangent-space normal map used in shading to simulate fine surface detail without increasing geometric complexity. The tangent space is defined by three basis vectors at a surface point: the normal (N), the tangent (T), and the bitangent (B). A tangentnormal encodes a surface normal in this local, surface-aligned coordinate system, so lighting calculations can account for micro-geometry while remaining in world or view space during rendering.

In practice, a tangentnormal is stored as color data in a texture, often encoded as RGB where each channel corresponds to a tangent-space axis. The normal vector components, originally in the range [-1, 1], are mapped to [0, 1] for storage. During shading, the tangentnormal is unpacked, transformed from tangent space to the appropriate space (usually world or view space) using the TBN matrix, and then used to perturb the surface normal for lighting calculations.

Tangentnormals are a staple of normal mapping, a widely used technique in modern rendering and physically based rendering (PBR). They are typically generated by baking from a high-polygon model to a low-polygon version, or created procedurally in texturing software. The approach relies on a consistent tangent basis, as mismatches in tangent, bitangent, or normal orientation can produce visual artifacts such as shading seams or distorted highlights.

Common considerations include differences in conventions between rendering engines (such as coordinate handedness and channel mappings), potential artifacts from non-uniform scaling, and the need to ensure proper normalization and re-orthogonalization of the tangent basis to maintain accurate shading.