# PBR Materials for Tissue (project-scoped)

Constrains material work to a small, deliberate set of tissue-like PBR patterns. The material inventory is fixed; the goal is to tune them, not multiply them.

## When to use
Load before creating, editing, duplicating, or assigning any `.mat` under `Assets/Materials/LaparoscopicBenchmark/`, or diagnosing "plastic-looking tissue", "mucosa too dry", "specular too harsh", or "normal map stretched" reports.

## Material inventory (do not duplicate blindly)

| Material | Purpose | Tunable axes |
|---|---|---|
| `Tissue_Default.mat` | "Clean" tissue reference | roughness, normal scale, albedo tint, AO |
| `Tissue_Wet.mat` | Wet specular variant for Scenario_02 | higher specular tint, lower roughness, slight clearcoat |
| `Tissue_LowTexture.mat` | Low-texture variant for Scenario_03 | uniform albedo, minimal normal, low contrast |
| `CavityWall.mat` | Moist wall of the cavity | roughness, normal scale, subsurface tint, specular tint |
| `InstrumentProxy.mat` | Instrument placeholder | metalness 1.0, low roughness, neutral albedo |

New variants: add to `Assets/Materials/LaparoscopicBenchmark/` with name ending in scenario tag, e.g., `Tissue_Wet_S04.mat`. **Do not rename the five canonical materials.**

## Available textures

- `Assets/Textures/LaparoscopicBenchmark/TissueMucosa.png` — canonical mucosa base map.
  - sRGB: **on**. Alpha Source: None. Max Size: 1024 (or 2048 for hero work). Compression: BC7/ASTC.
- `Assets/Models/FabOrgans/StylizedDigestiveSystem_{Diffuse,Normal,Roughness}.png` — stylized organ set.
- `Assets/Models/organs/textures/` and `archive.fbm/` — do not move (FBX references by relative path).

## URP/Lit PBR defaults for tissue

- **Shader**: `Universal Render Pipeline/Lit` (metallic workflow, opaque surface).
- **Render Face**: Front. **Double Sided**: off (except cavity wall when viewed from inside).

| Property | Tissue_Default | Tissue_Wet | Tissue_LowTexture | CavityWall | InstrumentProxy |
|---|---|---|---|---|---|
| Base color | warm pink-red ~`#B66A6A` | warm pink-red | uniform pink-red | deep red ~`#7A2A2A` | neutral metal ~`#C8C8C8` |
| Metallic | 0.0 | 0.0 | 0.0 | 0.0 | 1.0 |
| Smoothness | 0.35 | 0.55 | 0.20 | 0.40 | 0.85 |
| Normal Map | TissueMucosa normal | same | none / flat | cavity bump at low scale | none / flat |
| Normal Scale | 0.5–1.0 | 0.5–1.0 | n/a | 0.3–0.7 | n/a |
| Emission | off | off | off | off | off |

These are **starting points**, not finals. Confirm by screenshot.

## Diagnosis guide

| Symptom | Likely cause | Fix |
|---|---|---|
| Tissue looks plastic | `_Smoothness` too high | Lower to 0.25–0.35 |
| Mucosa too dry | `_Smoothness` too low | Raise to 0.4–0.5 |
| Specular too harsh | `_Metallic` > 0 on tissue | Set `_Metallic` to 0 |
| Normal map stretched | UV scale mismatch | Adjust material tiling, not mesh scale |
| Tissue reads as emissive | Emission on | Set Emission to black |

## Hard limits

- Never set `Metallic > 0` on tissue or cavity wall.
- Never set `Emission > 0` on tissue.
- Never use `Standard` (Built-in) shader.
- Never use procedural textures without explicit approval.
- Never rename the five canonical materials.
- Never create a material with a clinical term in the name.

## Common MCP calls

```
# Read a material
mcp__UnityMCP__manage_material(action="get_material_info", material_path="Assets/Materials/LaparoscopicBenchmark/Tissue_Default.mat")

# Set a property
mcp__UnityMCP__manage_material(action="set_material_shader_property", material_path="...", property="_Smoothness", value=0.42)

# Set a colour
mcp__UnityMCP__manage_material(action="set_material_color", material_path="...", property="_BaseColor", color=[0.71, 0.42, 0.42, 1.0])

# Assign to renderer
mcp__UnityMCP__manage_material(action="assign_material_to_renderer", material_path="...", target="...", search_method="by_name", slot=0)
```