Environment wear pipeline

Rephrased environments read as ruins, so every building module carries edge wear: rounded edges, chips, cracks and scratches. Artists model a clean low poly. Houdini generates the worn high poly, Substance Painter bakes it down, and Unreal layers materials on top using the baked masks.

The pipeline is a working prototype. One test asset runs through every step below.

Flow

Step	Tool	In	Out
1. Model	Your modeling package	Concept, block-out	Unwrapped low poly FBX
2. Sculpt	Houdini, Rephrased Auto Sculpt	Low poly FBX	SM_<name>_high.obj
3. Bake	Substance 3D Painter	Low poly + high poly	T_<name>_N, T_<name>_MASKS
4. Material	Unreal Engine	Low poly FBX + the two textures	Material instance on the mesh

The low poly never changes after step 1. The high poly exists only to be baked and stays out of Unreal.

Low poly requirements

• Centimetres. A building reads in the hundreds of units. The tool shows the model size at the top of its panel.
• One UV set, no overlaps. Every face gets its own texture space.
• UVs strictly inside 0–1. A vertex at -0.001 stops the bake project from loading.

• No faces buried inside other blocks. Where one block pushes into another, delete or trim the hidden faces. A face that is partly buried bakes with a sawtooth edge along its visible rim, and buried faces spend texture space on surfaces nobody sees.

• Split large structures into kit pieces. Texture sharpness comes from texel density. A whole 7 m building on one 4096 map holds about 3.5 pixels per centimetre; a 2 m kit piece on its own 2048 map holds about 10.

Step 2: Houdini

Rephrased Auto Sculpt is a Houdini digital asset. It runs in Houdini 22.0 or newer, including the free Apprentice edition. The tool lives in the depot under tools/rephrased-auto-sculpt/:

File	Contents
RephrasedAutoSculpt_v2.1.zip	The tool, a starter scene, an example mesh and a README. Unzip it anywhere outside the depot.
RephrasedAutoSculpt_Guide.pdf	An 11-page illustrated walkthrough of the steps below.

1. Open RephrasedAutoSculpt_Start.hipnc, or install otls/rephrased_auto_sculpt.hdanc through Assets > Install Asset Library.

2. Load your low poly in a File node and wire it into the tool's first input.

   

3. Set Detail Size to 2–3 while tuning. Adjust Wear Strength, Seed, and the Chips, Cracks, Scratches and Surface sections. Every control has a tooltip.

   

4. Press Paint Wear to choose where wear goes: drag for more, Ctrl+drag for none, Shift+drag to return to normal. Toggle Preview in the floating panel shows the sculpt while you stay in the brush.

   

5. Save the scene, set Detail Size to 0.75, and press Export High + Low (OBJ).

Keep Chips > Largest near 6 cm and Max Depth near 2 cm. A normal map changes shading, not silhouette, so large breaks belong in the low poly.

Step 3: Substance Painter

Painter bakes the high poly onto the low poly and produces two textures. It is used only for baking and masks; the look is built in Unreal.

Bake settings

Setting	Value
Output size	4096
Antialiasing	Subsampling 4x4
High definition mesh	SM_<name>_high.obj
Mesh maps	Normal, World space normal, Ambient occlusion, Curvature, Position, Thickness
Normal format	DirectX

Smart material: Rephrased_Masks

Apply it after baking. It contains three fill layers and exists only to generate masks, so the model looks black and glossy in the viewport.

Layer	Channel	Mask
Dirt_Roughness	Roughness = 1	Dirt generator: Dirt Level 0.4, Dirt Contrast 0.4, Grunge Amount 0.2, Edges Masking 0.3
Curvature_BaseColor	Base color = white	Curvature generator: Sharp 1, Fine 0.6, all broader scales 0, Global Balance 0.38, Global Contrast 0.45
Base	Base color, roughness, metallic = 0	None

Export

Each asset exports two PNG files:

File	Contents
T_<name>_N	Normal map, DirectX
T_<name>_MASKS	R = curvature (edges, cracks, chips), G = dirt (crevices and junctions), B = ambient occlusion

The MASKS texture looks like neon colours because three unrelated masks share its channels.

Step 4: Unreal

The material setup follows the layered material approach: a master material holds the layer stack, material layers define surfaces, and material layer blends decide where each layer shows.

Import settings

Texture	sRGB	Compression
T_<name>_N	Off	Normalmap
T_<name>_MASKS	Off	Masks

Master material

The master material is still a work in progress. It is a layered material with one input for the baked normal map, which always sits on top of the layers.

How the masks are used

A material instance of the master takes the asset's normal map and builds its look as a stack of layers:

Layer	Surface	Shown where
Background	A surface layer, such as stone	Everywhere
Edge highlights	A flat light colour	The red channel of the MASKS texture
Dirt	A flat dark colour	The green channel of the MASKS texture

Each mask-driven layer uses a layer blend that reads one channel of the MASKS texture, with an intensity control.

Running steps with an agent

Houdini, Painter and Unreal each expose an MCP server, so an agent can run the sculpt export, the bake, the mask export and the Unreal import on request. Painter must be started with --enable-remote-scripting, and the Painter and Unreal applications must be open.

The Unreal editor closes if an agent writes list or struct properties (a layer stack, an attribute list) through the generic property tool. Agents create nodes, wire them and set simple values; layer stacks are built by hand in the Layer Parameters tab.

Troubleshooting

Symptom	Cause	Fix
Sawtooth along the edge of a face	The face is partly buried in a neighbouring block	Trim the hidden part in the low poly
Rainbow or streaked patches in the normal map	The face is fully buried	Delete it from the low poly; it is not visible in game
Textures look soft up close	Low texel density	Bake at 4096 with antialiasing; split the asset into kit pieces
Large black blobs in the curvature mask	Broad curvature scales are on	Use the Rephrased_Masks generator values above
Painter refuses to load the mesh in a UV tile project	UVs fall outside 0–1	Move them inside
Round columns chipped all over in Houdini	Facet edges count as sharp	Raise Sharp Edge Angle to 60 or more
Brush strokes erase in Houdini	The F key swapped the brush values	Press Paint Wear again

Change history

• 2026-10-09 — Gabriel Li — Added the environment wear pipeline: Houdini auto sculpt, Painter bake and masks, Unreal layered material setup.