reference-to-3d

MCP backend

Use when: User supplies reference images/templates/texture atlases/orthographic views and wants a model matching them, or repeated visual mismatch feedback requires a reference-locked corrective loop.

Before the first Blender call, read ../text-to-blender/references/mcp-backends.md. Prefer official MCP for shared capabilities; preserve the selected backend for the whole task. Tool names in recipes are client/legacy examples: map them through that reference and its agent-host guide.

Reference-to-3D Reconstruction

This skill is for source-locked modeling: the reference asset is the contract. Do not generate a plausible object from memory and then decorate it. Extract measurements, part counts, silhouettes, and UV regions from the supplied files first, then build the Blender model to satisfy those measurements.

1:1 reconstruction upgrade

When the user requires true 1:1 matching, chain these skills instead of attempting another plausible modeling pass:

1. reference-analysis-validator for manifest, masks, part counts, overlay gates.
2. orthographic-registration for front/side/back/top coordinate agreement.
3. contour-to-mesh for silhouette-derived structural meshes.
4. atlas-uv-fitting for per-part texture/UV fitting.
5. mascot-logo-reconstruction as the full orchestrator for brand mascot/logo work.

Do not export a final asset until the validation JSON and overlay render pass the manifest thresholds.

Triggered failure mode

If the user says the output does not match the templates/textures/wireframes, stop regular text-to-blender generation and enter this workflow. Repeated plausible-but-wrong renders usually mean the missing step is reference analysis, not another modeling iteration.

Source-of-truth hierarchy

1. Front template / front wireframe: primary silhouette, visible part count, face/feature positions, brand read.
2. Texture atlas: exact part shapes, color/material boundaries, decals, lightmap/aura intent.
3. Side/back/top views: depth, stacking order, thickness, backside forms. They must not change the locked front projection.
4. User feedback: hard constraints; promote it into validation gates.

Mandatory preflight checklist

Before Blender modeling, write a small reference_manifest.json with:

{
  "source_files": [],
  "primary_view": "front",
  "expected_primary_parts": {"count": null, "labels": []},
  "structural_parts": [],
  "decorative_parts": [],
  "texture_regions": [],
  "validation_thresholds": {
    "front_mask_iou_min": 0.90,
    "bbox_center_tolerance_px": 12,
    "part_count_exact": true
  }
}

If the expected part count is unclear, derive it from the reference sheet with the analyzer and show the user the uncertainty instead of guessing.

Pipeline

1. Inventory and classify sources

Classify each provided asset:

• front_template: hero brand image or front wireframe.
• side_view, back_view, top_view: orthographic depth references.
• texture_atlas: basecolor / albedo atlas containing pieces.
• decal: transparent face/expression or detail layer.
• emissive, roughness, bump, normal, lightmap: material maps.
• aura/background: optional visual context, not structural body geometry.

2. Analyze images locally

Use scripts/template_analyzer.py for first-pass component extraction:

python3 ${CLAUDE_SKILL_DIR}/scripts/template_analyzer.py   --image /path/to/front_reference.png   --out /tmp/front_analysis.json   --mode edges  # use bright_on_dark/dark_on_bright/alpha when cleaner

The analyzer returns components with area, perimeter-derived score, bbox, centroid, contour, and approximate class hints. Use --mode edges for faint grey wireframes and Otsu modes for clean masks/atlases. Treat this as measurement input, not final authority.

3. Lock the front reference in Blender

Create a front reference plane or Image Empty in the same orthographic camera used for validation. Prefix it REF_ and exclude it from export. Official Blender docs describe Image Empties as reference images/blueprints and support front/back depth, opacity, orthographic-only display, and axis-aligned display.

4. Build geometry from source contours

For each structural part:

1. Convert the 2D contour to front-view X/Z coordinates.
2. Generate a quad strip/grid inside that contour.
3. Assign Project-from-View-style UVs based on front X/Z bounds or exact atlas region.
4. Add only shallow Y-depth/crown/extrusion after the front silhouette is locked.
5. Keep part names semantic: GEO-subject_part_top, GEO-subject_face_shell, etc.

Do not radial-duplicate a mascot unless the reference is truly radial. Logos often have occlusion, intentional asymmetry, and a fixed visible part count.

5. Multi-view registration

• Front X/Z is locked first.
• Side view controls Y/Z depth envelope only.
• Top view controls X/Y spread only.
• Back view controls hidden/backside geometry and validation, not front silhouette.

If views disagree, keep the front brand read and document the conflict.

6. UV and texture mapping

Chain-load blender-uv-texturing when any texture pack is provided. For atlas-driven parts:

• crop or map per atlas region; do not project the whole atlas onto every part;
• front-facing hero surfaces use front-projected UVs;
• side/back surfaces use side/back UV islands, procedural fill, or baked colors;
• alpha decals need transparent material settings and must not introduce black planes;
• lightmaps are optional realtime helpers and should not be connected as emission unless specified.

7. Validation gates before export

Always produce:

• front_preview.png
• front_overlay_reference.png
• front_mask_validation.json
• side_preview.png
• back_preview.png
• top_preview.png

Use scripts/silhouette_validator.py:

python3 ${CLAUDE_SKILL_DIR}/scripts/silhouette_validator.py   --reference /tmp/reference_mask.png   --render /tmp/render_mask.png   --out /tmp/validation.json

Refuse final export if:

• primary part count differs from manifest;
• front-mask IoU is below threshold;
• face/feature centroid is outside tolerance;
• optional aura/decorations are included in the base GLB by mistake.

Blender code patterns

Reference plane in front-view X/Z

import bpy

def create_reference_plane(name, image_path, width, height, y=0.2, alpha=0.35):
    img = bpy.data.images.load(image_path, check_existing=True)
    mat = bpy.data.materials.new('MAT-' + name)
    mat.use_nodes = True
    nodes = mat.node_tree.nodes
    bsdf = nodes.get('Principled BSDF')
    tex = nodes.new('ShaderNodeTexImage')
    tex.image = img
    mat.node_tree.links.new(tex.outputs['Color'], bsdf.inputs['Base Color'])
    mat.node_tree.links.new(tex.outputs['Alpha'], bsdf.inputs['Alpha'])
    bsdf.inputs['Alpha'].default_value = alpha
    mat.blend_method = 'BLEND'
    verts = [(-width/2,y,-height/2),(width/2,y,-height/2),(width/2,y,height/2),(-width/2,y,height/2)]
    mesh = bpy.data.meshes.new(name + 'Mesh')
    mesh.from_pydata(verts, [], [(0,1,2,3)])
    mesh.update()
    uv = mesh.uv_layers.new(name='UV')
    for li, uvco in zip(mesh.polygons[0].loop_indices, [(0,0),(1,0),(1,1),(0,1)]):
        uv.data[li].uv = uvco
    obj = bpy.data.objects.new('REF-' + name, mesh)
    bpy.context.collection.objects.link(obj)
    obj.data.materials.append(mat)
    obj.hide_render = True
    return obj

Validation print contract

print('VALIDATE expected_primary_parts=', expected, 'actual=', actual)
print('VALIDATE front_locked=True reference_overlay_rendered=True')
if actual != expected:
    raise RuntimeError('Part-count mismatch; refusing export')

When to stop and ask for human input

Ask for a correction only after generating evidence, e.g. an overlay image or JSON showing ambiguity. Do not ask vaguely. Example: “The analyzer finds N prominent structural components plus M faint background/decorative shapes. Should the GLB include only the structural components?”

Sources distilled

• Blender Manual: Image Empties for reference images/blueprints; front/back display, opacity, orthographic and axis-aligned controls.
• Blender Manual: Trace Image to Grease Pencil works best from manually prepared black/white images and controlled resolution.
• Blender Manual: Shrinkwrap moves vertices to a target surface and is useful after silhouette lock for conforming secondary details.
• Blender Manual: UV/Image Texture and Project-from-View-style workflows require UV maps and material nodes for renders/exports.
• OpenCV docs: contour moments, area, perimeter, bounding boxes, template matching.
• scikit-image docs: SSIM for image similarity when pixel-MSE is not perceptually meaningful.