Smoothing Groups
Per-face shading split
Also known as: Smoothing normals · Hard edges · Smoothing
Definition
Smoothing groups (called "hard edges" in Maya/Blender) control which faces of a mesh share averaged vertex normals — making them shade smoothly — versus which faces produce a sharp lighting break. They are the single most important per-vertex attribute beyond position and UV: identical geometry with different smoothing settings will look like two completely different surfaces under lighting. Always set hard edges along UV seams to avoid baking errors.
In production
Standard rule: every UV seam should also be a hard edge, and every hard edge should be a UV seam. This avoids the gradient artefacts caused by synced vs non-synced tangent-space normal bakes. Marmoset Toolbag exposes this in its baker as "Use Hard Edges".
Learn Smoothing Groups in
Tools that use Smoothing Groups
See also
Tangent Space
Local coordinate system for normal maps
Normal Map
Per-pixel surface detail
Baking
High-poly detail → low-poly texture
UV Mapping
Unwrapping 3D meshes to 2D
Edge Flow
Direction of polygon edges across a surface
Faceted Shading After Import
Smooth mesh looks flat-shaded in the engine
Weighted Normals
Smooth shading that keeps crisp edges
Flipped Normals
Faces pointing inside out
Shade Smooth Artifacts in Blender
Dark patches after Shade Smooth and missing Auto Smooth
Maya Shading Faceted or Too Smooth
Soften and harden edges