generate-3d

name	generate-3d
description	Generate one atomic 3D asset via fal Tripo P1 (textured, PBR auto-included, $0.50). Polycount tuned per object class — sweet spot 5,000-15,000 faces. No fallback (Trellis 2 quality is worse for stylised cases; retry P1 with a better reference plate instead).

Codex adaptation

Use the available Codex shell and file tools. In this migrated skill, $1 means world slug and $2 means object id.

Generate exactly one 3D asset for worlds/$1/assets/$2.glb.

Inputs

• $1 = world slug
• $2 = object id (from plan.objects[].id)
• The object's name, scale_hint, priority, and (new) face_limit come from worlds/$1/plan.json.

Procedure

1. Pick the face_limit for this object. Tripo P1 generates clean meshes in the 5,000-15,000 face range. Anything below = blocky, above = wasted detail you'll never see in a stylised scene. Match to the object class:

   Object class	face_limit	Why
   Hero structural (tiki hut, treasure chest, beach hut, lantern post)	12,000-15,000	Visible silhouette, multiple read-at-distance parts
   Hero organic (tall palm, big rock, bent palm, statue)	10,000-13,000	Smooth curves need a bit more geometry to read cleanly
   Mid-detail (medium rock, barrel, conch shell, starfish)	7,000-9,000	Recognisable shape, no microdetail
   Filler (pebble, small shell, twig, debris)	5,000-6,000	Generic prop — won't be looked at closely

   If the plan already specifies a face_limit, use that. Otherwise pick from the table by scale_hint + priority.

   Never request face_limit > 15,000. The wrapper clamps to [5,000, 15,000] regardless — but the prompt should match the budget so you don't waste a generation on detail the clamp will discard.

2. Build the generation prompt. Combine object.name + plan.style.anchor + plan.style.level_of_stylization:

   "{name}, {anchor} cartoon art style, {level_of_stylization} stylisation, vibrant saturated palette ({palette[0]}, {palette[2]}), isolated on white background, centred, no shadows, single object only, simple readable silhouette, no microdetail."

   The "simple readable silhouette, no microdetail" tail is important — biases the reference image (and thus the Tripo output) toward shapes that fit the 5-15k face budget.

3. Generate the reference plate (image input to Tripo). Use nano-banana text-to-image at $0.039:

   node .claude/scripts/asset-pipeline/nano-banana-edit.mjs \
     --prompt "<the prompt above>" \
     --output-dir worlds/$1/assets \
     --output-slug $2-ref
   

   This produces worlds/$1/assets/$2-ref.png — a clean, white-bg reference of the object.

4. Generate the 3D asset via Tripo P1 textured ($0.50, includes PBR in the pbr_model output URL):

   node .claude/scripts/asset-pipeline/tripo-p1.mjs \
     --image worlds/$1/assets/$2-ref.png \
     --output-dir worlds/$1/assets \
     --output-slug $2 \
     --texture true \
     --face-limit <picked-from-table>
   

5. If the result is poor — retry with a better reference plate. Read the preview (Tripo includes one in the request metadata). If the mesh / texture clearly fails (mangled silhouette, wrong colours, broken topology), do NOT fall back to a different model. Instead:

   • Regenerate the reference plate with a tightened nano-banana prompt (add "single object, white background, no shadows, centred, no clipping, full object visible").
   • Re-run Tripo P1 with a different --seed.
   • Cap at 2 retries per object. After that, escalate to the user with the failed preview attached.

   Why no Trellis 2 fallback: stylised scenes degrade visibly when half the assets are from a lower-quality model. The project default is to fail explicitly rather than silently swap in a mid-tier result.

6. Update plan.json. Add the asset path + cost + face_limit to the object entry:

   "objects": [
     {
       "id": "$2",
       ...
       "asset_path": "worlds/$1/assets/$2.glb",
       "pbr_asset_path": "worlds/$1/assets/$2-pbr.glb",   // optional — present when texture=true
       "cost_usd": 0.50,
       "face_limit": 10000,
       "provider": "tripo3d/p1"
     }
   ]
   

7. Log cost. Append to worlds/$1/cost.json. Reconciler runs once at end-of-Phase-2.

Returns

• Path to the generated .glb
• (Optional) path to the PBR variant
• Cost in USD
• Face limit used
• Provider used (tripo3d/p1 or fal-ai/trellis-2)
• If a fallback happened, the reason

What you must NOT do

• Do NOT request face_limit > 15_000 — wasted detail, wasted tokens explaining it.
• Do NOT use quality: "high" — that's not a real Tripo P1 param; the wrapper would silently drop it.
• Do NOT generate the same object id twice — check worlds/$1/assets/$2.glb exists before kicking the gen.

Parallelisation note

Designed to be invoked N times in parallel from build-world. fal handles parallel queues; the only contention is the local cost.json file — read-modify-write with a small file lock, or rebuild from request-metadata records at the end of Phase 2.