@Malven31

Adding foliage support to wow.export

I've written this document based on what Claude Opus 8 helped me dig up. Even if I have checked its sayings, I'm not a WOW expert, so take it with caution.

Wow Export

What WoW needs to place foliage

Ground-effect doodads are driven by three things:

1. Which doodad set : each terrain layer references a GroundEffectTexture row (via effectID) that lists the doodad models and their density/weights.
2. Where it can appear : the per-layer alpha weight inside each chunk (already exported as the tex_<tile>_<chunk>.png alpha texture, one layer per R/G/B/A channel). This is currently not exported if Terrain Textures are exported (can't export both, they have the same names).
3. Per-cell gating : within each chunk WoW further gates doodads on an ×ばつ8 "detail cell" grid using two MCNK header fields. This is the missing piece.

Already exported today

• tex_<tile>_<chunk>.png : RGBA alpha weights, one terrain layer per channel (if "Alpha Textures" only, as "Terrain Textures" are combined/baked RGB textures without Alpha Texture's informations).
• tex_<tile>_<chunk>.json : per-layer descriptors (layer index, effectID, channelIndex, etc. Only exported if exporting "Alpha Textures", not "Terrain Textures").
• foliage/<effectID>.json : the GroundEffectTexture row (density + weights).

Missing data (the gate)

Two per-cell MCNK header fields fully control whether doodads are emitted in a given detail cell. wow.export already parses both in ADTLoader.js but never writes them out:

• noEffectDoodad : uint1_t[8][8] packed as a 64-bit bitmap (MCNK header 0x050). A set bit means "no doodads in this cell".
• predominantTexture / lowQualityTextureMap : uint2_t[8][8] (MCNK header 0x040), eight int16 rows. Each 2-bit value (0–3) is the index of the predominant terrain layer for that cell. WoW only spawns a layer's doodads where that layer is predominant, so this prevents every overlapping layer's foliage from stacking in the same cell.

What I've implemented in my tests

I've added a unpackDoodadGating(rootChunk) helper that returns two flat, 64-entry, row-major arrays (index = row * 8 + col):

• noEffectDoodad[i] : 0 or 1, from BigInt bit i of the packed field.
• predTex[i] : 0–3, from (lowQualityTextureMap[row] >> (col * 2)) & 0x3.

And written both into each chunk's tex_<tile>_<chunk>.json (e.g. as noEffectDoodad and predTex properties). Applied in both export paths:

• src/js/3D/exporters/ADTExporter.js (current split-alpha path).
• src/js/modules/legacy_tab_maps.js (legacy split path).

Orientation gotcha (document this for consumers)

The alpha PNG is written bottom-up (the exporter flips rows, v = 1 - row), but these gating arrays are written in raw header order (index 0 = MCAL row 0 = top). A consumer sampling the alpha texture and the gating grid with the same UV must vertically flip the cell row for the gating lookup (cell_row = 7 - floor(v * 8)). Columns are not flipped. Failing to do this mirrors the gate and blanks the wrong cells.

Optional: Alpha Textures export along side Terrain Textures

In my tests, I've added an opt-in "Foliage Alpha Textures" checkbox (gated on 1K to 16K Terrain Textures choice) that writes the per-chunk alpha weights as standalone tex_<tile>_<chunk>_alpha.png images. This is convenient for tools that want the alpha weights as plain image data rather than re-deriving them, but it is independent of the gating data above.

Blender Addon

Philosophy

The Blender Foliage addon I've vibe coded consumes the exported data :

• Read the exported terrain' alpha textures tex_<tile>_<chunk>_alpha.png and foliage/<effectID>.json rows.
• For each terrain layer, scatter that layer's doodads with Geometry Nodes, using the alpha weight as density and the per-cell gating (noEffectDoodad + predTex) as an on/off mask.