3d-wood-material

• PROMPT.mddoc · 3,111 bytes
• SKILL.mdcore · 11,039 bytes
• agents/openai.yamlasset · 311 bytes
• demo.htmlasset · 37,628 bytes
• preview.jpgasset · 272,671 bytes

# 3D Wood Material

**Mechanism:** one small periodic noise field, mip-filtered, is read at several different stretches and scales inside the fragment shader, so ring position, latewood, pores, fibres, rays and tool marks all come from the same wandering grain and feed colour, roughness and relief together, each fading out by its own screen footprint.

Boundary. This skill is the wood surface itself. For whole-scene light, rays and scoring wood renders, use `3d-wood-lighting-scorecard`. For image-based PBR sets (downloaded maps, texel budgets, KTX2 delivery) use `3d-high-resolution-textures`; reach for it when you need a photographed or scanned species. For silhouette, bevel and LOD geometry use `3d-high-poly-models`; this skill only needs a rounded arris (below). Cloth, metal and paper have their own siblings.

Run `demo.html` first (Kibori bench, four species, four finishes, macro views, and a switch that swaps in the failure). `PROMPT.md` recreates it.

## Recipe

1. **Patch, do not replace.** Build `MeshPhysicalMaterial({color:0xffffff, roughness:max(0.43,r), ior:1.43, specularIntensity:0.72})` and edit it in `onBeforeCompile`: `#include <map_fragment>` multiplies `diffuseColor` by the wood colour, `#include <roughnessmap_fragment>` sets `roughnessFactor=clamp(roughness*W.rough,0.35,1)`, `#include <normal_fragment_maps>` replaces the normal with a screen-space bump of the wood height `W.h`. Lighting, shadows, IBL and tone-mapping stay stock. The vertex stage only passes object-space position `vOP` and the object normal.
2. **Bake one field.** A 1024² `RepeatWrapping`, `LinearMipmapLinear`, `NoColorSpace` render target of periodic gradient noise (period 64, three octaves: `.r` base, `.g` fbm 0.60/0.27/0.13, `.b` a shifted copy). Reading it as `texture(p/64)` costs one tap. All timber shares it; per-board difference is a seed offset, not a texture.
3. **Grain axis.** `uAxis` 0/1/2 picks the log axis; `along` is that coordinate and `cross2` the other two. `endgrain = pow(|n·axis|, 6)` flips pores from streaks to open cells and dulls the colour on cut faces.
4. **Rings.** Drift the pith with two slow fields, `radius=|(cross2+(-drift, offAxis+0.48))*(1,0.56)|`, `growth=radius*ringFreq` plus fbm wobble (`±1.25` rings), `ring=floor(growth)`, `phase=fract`. Each ring draws its own width from `annual` noise: `lateWidth=0.065+annual*0.21`. Latewood is a steep `smoothstep(0.94-w, 0.97-w, phase)` cut off by `1-smoothstep(0.965,1,phase)`. Small `offAxis` gives cathedral arcs; large `offAxis` gives straight quarter-sawn lines.