Macro normals

A macro normal is a normal map baked one-to-one from a sculpt that holds only the asset's large forms: the big planes, ridges and breaks of a rock or cliff. Small detail does not live in it. That comes from tiling materials blended on top in the shader. The result is a unique-looking asset that needs only a modest unique texture.

Jared Sobotta's rock set for The Last of Us Part I is the clearest published example: the high-poly sculpts were used for "1x1 Macro normals", while the surface came from "1-3 tiling rock materials, lichen, grunge, and moss inside of the shader" (ArtStation: Rock Breakdown).

#How it works

A macro normal workflow has two layers, each on its own UVs:

1. The macro layer. A unique bake from the sculpt, on the asset's normal (non-overlapping) UVs. "1x1" means one texel position per point on the surface, as in any unique bake; see baking.
2. The detail layer. One or more tiling materials, with their own normal maps, repeating across the surface many times.

The shader combines the two normals, and usually uses the macro layer's information to steer where moss, dirt or a second rock material appears.

Sobotta describes the sculpting goal accordingly: "the fidelity I was going for mainly was the largest scale shapes" (ArtStation: Rock Breakdown). If the sculpt also carried small cracks, they would clash with the tiling material's cracks, at a different scale and direction.

#Why studios use it

• Memory. A tiling material can be shared by every rock in a level. Only the macro bake is unique, and because it holds only large, soft shapes it survives at a lower resolution than a fully detailed bake would.
• Consistency. A whole set of rocks that shares the same tiling materials looks like one geology. Sobotta's rocks all draw from the same small group of materials (ArtStation: Rock Breakdown).
• Close-up sharpness. Tiling detail stays crisp at any distance from the camera, which a single unique texture stretched over a 20 m cliff cannot. Epic's detail-texture documentation makes the same argument: a highly repeated texture over the base stops a material "looking pixelated when it is viewed very closely" (Unreal Engine documentation: Adding Detail Textures to Unreal Engine…).

#Blending the two normals

Two normal maps cannot be combined by simply adding or multiplying their colours. Colin Barré-Brisebois and Stephen Hill explain why: "Since the data represents directions, we can't simply treat the channels independently as we do for colours" (Self Shadow: Blending in Detail). Their article compares common methods and introduces reoriented normal mapping, designed so that "if one of the normal maps is flat, the output matches the other normal map" (Self Shadow: Blending in Detail). See normal map blending for the methods in detail.

#Common mistakes

• Sculpting fine detail into the macro sculpt. It doubles up with the tiling layer and creates conflicting scales (ArtStation: Rock Breakdown).
• Blending normals by adding colours. Use a proper normal blend (Self Shadow: Blending in Detail).
• Spending high resolution on the macro bake. It carries soft, large shapes; check whether a lower resolution looks the same in game.
• Mismatched tiling scale. If the tiling material's rock grain is larger than the macro forms, the two layers read as one confused surface.

#Related terms

normal map · normal map blending · detail maps and macro variation · tileable materials · baking · sculpting rocks and cliffs · primary, secondary and tertiary forms

#Further reading and watching