PBR Materials

The execution model is in blender-core. Measured values are in references/pbr-values.md.

Fast paths

• Texture set → material: scripts/build_pbr_material.py -- --name M_Crate --textures //tex/crate --objects SM_Crate. It detects maps by filename (Poly Haven, ambientCG, Substance, UE suffixes), sets color spaces, splits ORM, flips DirectX normals, and routes AO to glTF.
• Solid physically-plausible material: --preset gold|iron|plastic|rubber|wood|glass|skin|... with an optional --color R G B (sRGB).

The rules (violations are what make renders look "CG")

1. Metallic is binary: 0 (dielectric) or 1 (raw metal). Use in-between values only on transition pixels (dust or rust edges on metal). Painted metal counts as dielectric.
2. Base color = albedo with no lighting: no baked shadows/AO/highlights. Dielectric range is sRGB ~30, 240 (linear 0.012, 0.87): charcoal ≈ 50, fresh snow ≈ 240. Metals: base color = F0 reflectance, sRGB 180, 255, never dark.
3. Roughness carries the realism. Break it up with grunge, smudges and wear. A constant roughness value looks fake; vary it ±0.1, 0.2 across a surface.
4. Color spaces: Base Color and Emission use sRGB. Roughness, Metallic, Normal, AO, Height, Opacity and ORM use Non-Color. A wrong color space is the #1 bug (washed-out normals, wrong roughness).
5. Specular: leave IOR 1.5 and Specular IOR Level 0.5 for almost all dielectrics. Change IOR only for known materials (water 1.33, glass 1.5, diamond 2.42).
6. Normal maps: Blender, glTF, Unity and Roblox use OpenGL (Y+). Unreal and Substance's DirectX preset use DirectX (Y-), so flip G when converting. The bake and the target must use the same tangent basis (MikkTSpace) and the same triangulation.
7. AO: the Principled BSDF has no AO input. For engines, ship AO in the ORM red channel. For Cycles renders, don't multiply AO into base color, because the renderer computes occlusion.