blender-to-unity

# Blender → Unity Model Handoff Bring whatever model is currently in Blender into the open Unity scene. The seam is the local filesystem: Blender exports a file, Unity imports it. The two servers never talk directly. ## Preconditions - Both `mcp__blender__*` tools and MCP for Unity tools are connected. - A model exists in the Blender scene (confirm with `mcp__blender__get_scene_info` / `mcp__blender__get_object_info`). If empty, stop and tell the user — this skill does not generate models. - **`import_model_file` is in the `asset_gen` tool group, which is off by default** (only `core` loads). Enable it first with `manage_tools` (enable the `asset_gen` group), **or** call the C# handler straight through `batch_execute` — `{"tool":"import_model_file","params":{"sourcePath":...,"name":...,"outputFolder":...}}` (camelCase) — which dispatches by name regardless of group gating. ## Steps 1. **Resolve the Unity project path.** Read `mcpforunity://editor/state` for the project root (the editor dataPath's parent). Decide the export format: - **GLB (glTFast) when the model has a rig, animation, PBR (metallic/roughness), emission, or transparency** — glTFast carries all of these automatically, no post-processing (see [references/bridge-fidelity.md](references/bridge-fidelity.md)). Multi-material zones survive either format, so they alone don't force GLB. - **FBX otherwise** — when glTFast isn't installed, the model is plain geometry, or you specifically need the built-in importer's humanoid-avatar pipeline. FBX drops emission/metallic (Step 5 restores emission) and surfaces animation only with `animation_type` set (Step 3). 2. **Export from Blender to a temp path** via `mcp__blender__execute_blender_code`: ```python import bpy, os, tempfile out = os.path.join(tempfile.gettempdir(), "blender_to_unity.fbx") # Export the selection if any, else the whole scene: bpy.ops.export_scene.fbx(filepath=out, use_selection=bool(bpy.context.selected_objects), apply_unit_scale=True, bake_space_transform=True) print(out) ``` (glTF branch: `out_glb = os.path.join(tempfile.gettempdir(), "blender_to_unity.glb")`, then `bpy.ops.export_scene.gltf(filepath=out_glb, export_format='GLB', use_active_scene=True)` — its default `use_active_scene=False` can silently export a *different* open scene.) 3. **Import into Unity** with `import_model_file`: `import_model_file(source_path=<temp path>, name=<asset name>, target_size=<final size in meters>)`. For a **rigged/animated FBX**, also pass `animation_type="generic"` (or `"humanoid"`; `"legacy"` targets the old Animation-component system) — the importer defaults to `"none"`, which deliberately imports the mesh with **zero animation clips**. GLB ignores this (glTFast imports animation itself), so it's an FBX-only knob. It returns `{ asset_path, asset_guid }`. Pass `target_size` as the intended final size, but treat it only as a hint: it rescales at import solely when the project's **Auto-normalize** pref is on, and even then is unreliable for Blender FBX (see the **Scale** note). Step 4 does the reliable normalization. 4. **Place it in the scene, normalized to size.** Ensure the scene has a camera + directional light (`manage_scene` / `manage_gameobject`). Instantiate the model at the chosen position via `manage_gameobject(action="create", prefab_path=<asset_path>, name=<asset name>, position=[x,y,z])`. Then normalize its size deterministically — Blender FBX commonly imports ~100× too large — by measuring the placed model's world bounds and scaling so its largest dimension equals your target size. Run via `execute_code` (substitute your object name and target meters): ```csharp var go = GameObject.Find("<asset name>"); var rs = go.GetComponentsInChildren<Renderer>(); var b = rs[0].bounds; for (int i = 1; i < rs.Length; i++) b.Encapsulate(rs[i].bounds); float maxDim = Mathf.Max(b.size.x, Mathf.Max(b.size.y, b.size.z)); float target = 2f; // intended size in meters if (maxDim > 0.0001f) go.transform.localScale *= target / maxDim; ``` 5. **Restore emission FBX dropped (FBX path).** Blender scenes commonly store their color/glow in *material emission* (and other Principled-node inputs). FBX carries base/diffuse color but **not emission**, so neon / "Tron" scenes import as dark bodies with black accents. If the import looks flat vs. Blender, restore it: a. Dump the emissive materials from Blender via `execute_blender_code`: ```python import bpy, json out = {} for m in bpy.data.materials: if not (m.use_nodes and m.node_tree): continue col, s = (0, 0, 0), 0.0 p = next((n for n in m.node_tree.nodes if n.type == 'BSDF_PRINCIPLED'), None) es = next((k for k in ('Emission Color', 'Emission') if p and k in p.inputs), None) # 4.x / 3.x name if es: col = tuple(p.inputs[es].default_value)[:3] s = float(p.inputs['Emission Strength'].default_value) e = next((n for n in m.node_tree.nodes if n.type == 'EMISSION'), None) if e and s == 0: col = tuple(e.inputs['Color'].default_value)[:3]; s = float(e.inputs['Strength'].default_value) if s > 0 and sum(col) > 0.01: out[m.name] = [round(col[0], 3), round(col[1], 3), round(col[2], 3), round(s, 3)] print(json.dumps(out)) ``` b. In Unity (`execute_code`): extract the FBX's materials so they're editable (`AssetDatabase.ExtractAsset` per `Material`, then `ImportAsset(fbx, ForceUpdate)`), then for each dumped name set `_EmissionColor = color * Mathf.Clamp(strength*0.45f, 1.5f, 5f)`, `EnableKeyword("_EMISSION")`, and `globalIlluminationFlags = RealtimeEmissive`. Match names **case-insensitively** — FBX mangles case and can split one material into variants (`EdgeCyan` → `EdgeCyan` + `EDGE_CYAN`); set every match. Add a global Bloom volume and enable the camera's `renderPostProcessing` so the emission actually glows. 6. **Verify** with `manage_camera(action="screenshot", include_image=true)` and report the asset path + a screenshot. ## Notes - **Scale.** Models from Blender almost always arrive at the wrong scale — its FBX unit handling makes them land ~100× too large in Unity. `import_model_file`'s `target_size` only rescales at import when the project's Auto-normalize pref is enabled, and its importer-level normalization is unreliable for Blender FBX (it can over- or under-shoot, e.g. a `target_size=2` model measured 200 m). The robust fix is the Step 4 measure-bounds-then-set-`localScale` routine, which hits the target size deterministically regardless of the import scale or the Auto-normalize pref. - **Materials & emission.** FBX carries base/diffuse color and transforms fine, but **drops emission and any node-based color** — so Blender neon / "Tron" scenes (color stored in emission) import as dark bodies with black accents. Two fixes: **(a) prefer glTF/GLB when glTFast is installed** — glTF's PBR model carries `emissiveFactor` + `KHR_materials_emissive_strength` natively, so emission survives with no post-step (`bpy.ops.export_scene.gltf(filepath=out, export_format='GLB', use_active_scene=True)`); **(b) with FBX, run Step 5** to dump Blender's emission and reapply it. Also check the mesh for a `color_attributes` (vertex color) layer — the *data* survives FBX, but URP Lit won't *display* it; that needs a vertex-color-reading shader, not `_EmissionColor`. - FBX is the default because glTFast is optional in MCP for Unity. If the import errors with "GLB import requires glTFast", re-export as FBX (or install glTFast from the Dependencies tab). - **Format fidelity.** [references/bridge-fidelity.md](references/bridge-fidelity.md) is a tested matrix of what each format carries. Summary: **GLB (glTFast)** keeps textures, metallic/roughness, emission, transparency, and animation automatically; **FBX** drops metallic + emission, needs `ModelImporter.animationType = Generic` to surface transform animation, and needs material/texture extraction to assign an embedded texture. Both bake modifiers and carry geometry + vertex-color *data* (URP Lit won't *display* vertex colors). Neither carries procedural/node materials — bake them to image textures in Blender first. - **Animation doesn't auto-play.** An imported clip won't move the model until an `AnimatorController` drives it — the placed model has an `Animator` with a **null controller**, so it looks frozen. Build one with `manage_animation` (`controller_create` → add the clip as a looping state → `controller_assign` onto the instance) rather than hand-rolling `execute_code`. See bridge-fidelity gotcha #7. - **Multi-material zones survive.** A mesh split into material slots in Blender (e.g. skin/shirt/pants regions) imports as submeshes with one material each — base colors carry over GLB natively — so you can "dress" a model with material zones and it arrives intact. - Keep one model per handoff; for batches, repeat the loop with distinct names. - This skill never sends API keys or file bytes over the MCP bridge — Unity reads the file from disk. - `import_model_file` copies only the single source file; for multi-file exports (a text `.gltf` with an external `.bin`, or an `.obj` with a sibling `.mtl`/textures), zip them first and pass the `.zip` — a bare `.gltf`/`.obj` will lose its sidecars.