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). 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:

   pythonCopy code
   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):

   csharpCopy code
   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:

   pythonCopy code
   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 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.