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.

Principled BSDF (5.2) quick map

Base Color, Metallic, Roughness, IOR, Alpha, Normal, Thin Wall (5.2: leaves/paper/fabric sheets without volume), Subsurface Weight/Radius/Scale (skin, wax; Scale in meters ≈ 0.005–0.02 for skin), Specular IOR Level, Specular Tint, Anisotropic, Transmission Weight (glass/liquids), Coat Weight/Roughness/Normal (car paint, varnish), Sheen Weight (cloth, velvet), Emission Color/Strength (strength in W/m²-ish units; 1–10 for screens, 50+ for bulbs), Thin Film Thickness/IOR (soap, oil, coated lenses), Diffuse Roughness.

Engine export rules

Target	Maps	Packing	Normal
glTF / web / Godot	baseColor(+alpha), metallicRoughness, normal, occlusion, emissive	glTF: R=AO G=Rough B=Metal (ORM)	OpenGL
Unreal	BaseColor, Normal, ORM	R=AO G=Rough B=Metal	DirectX (UE flips on import if the texture is marked)
Unity URP/HDRP	BaseMap, Normal, MetallicSmoothness / HDRP MaskMap	URP: R=Metal A=Smoothness (1-rough). HDRP Mask: R=Metal G=AO B=DetailMask A=Smoothness	OpenGL
Roblox SurfaceAppearance	ColorMap(+alpha), NormalMap, MetalnessMap, RoughnessMap, EmissiveMaskContent	separate grayscale maps, no packing	OpenGL, tangent space

• Only image-texture → BSDF chains export. Procedural nodes, Mix nodes and math become nothing in engines, so bake them first (blender-texture-baking).
• One material per texture set. Every extra material is an extra draw call (blender-game-optimization).
• Power-of-two textures (512/1024/2048/4096). Use PNG/TGA for data maps, never JPEG for normals.

Alpha

mat.surface_render_method = "DITHERED" (cutout/alpha-clip, sorts correctly, good for foliage/hair cards) or "BLENDED" (true transparency, glass/UI). Connect Alpha. glTF exports CLIP/BLEND from the alpha setup. Prefer dithered/clip for games.

Displacement

Height map → Displacement node → Material Output Displacement. mat.displacement_method: BUMP (shading only, everywhere), BOTH/DISPLACEMENT (Cycles, needs dense or adaptively subdivided geometry: Subdivision modifier use_adaptive_subdivision). Scale is in meters; midlevel 0.5 for 8-bit, 0 for 32-bit EXR.

View transform (judge materials under the right one)

scene.view_settings.view_transform: AgX (default, photographic), Khronos PBR Neutral (what-you-see-is-the-albedo; use for asset/product review and glTF parity), Standard (UI/graphics/textures that must match pixels), ACES 1.3/2.0 (VFX pipelines). Never bake or author textures while looking through Filmic/AgX with an extreme "Look".

Procedural → texture

Procedural setups (noise/voronoi wear, curvature masks via Geometry > Pointiness (Cycles) or Ambient Occlusion node, edge wear via Bevel node normals) are fine for renders. For engines, bake them to the texture set (blender-texture-baking). Node Wrangler (bundled) Ctrl+Shift+T does the same as build_pbr_material.py, but needs the UI.

Gotchas

• material.use_nodes is deprecated in 5.x. New materials already have Principled + Output.
• mat.diffuse_color only affects the viewport (Solid mode/workbench), not renders or export.
• Images loaded headless need image.colorspace_settings.name set before baking or export.
• Shared texture images used by several materials: change the color space once, because it's per image.