Wireframe-to-3D Conversion

Convert 2D orthographic wireframe images to parametric 3D Blender models, exported as glTF 2.0 binary (.glb).

Overview

The skill drives a four-stage pipeline:

1. Analyze wireframe images locally with scripts/wireframe_analyzer.py (OpenCV → Bezier control points in JSON).
2. Generate Blender Python code that recreates the contours as parametric Bezier curves.
3. Execute code in Blender via mcp__blender__execute_blender_code, converting curves to meshes with PBR materials.
4. Export as optimized GLB (≤ 15 MB), validating size and topology.

You (Claude) are the orchestrator. The scripts/ directory contains the only standalone code (wireframe_analyzer.py); everything else is patterns you emit and run via MCP.

Prerequisites — check first

Before any wireframe work, verify the environment:

1. Blender MCP is reachable. Call mcp__blender__get_scene_info. If it errors with "Could not connect to Blender", stop and tell the user:

   "Blender's MCP addon isn't running. Start Blender, enable the BlenderMCP addon (port 9876), then re-run."

2. Python deps for the analyzer. Run:

   python3 -c "import cv2, numpy, scipy" 2>&1
   

   If it errors, run pip install opencv-python numpy scipy Pillow (or instruct the user to).

3. Image input. Confirm the user provided at least one PNG. Reasonable bounds: ≥ 400×400 px, black-on-white or white-on-black line art.

Decision flow

Q1: How many views?

• Single view → flat 2D extrusion only (warn the user; depth must be supplied or assumed).
• Front + side → full 3D reconstruction (silhouette × depth profile).
• Front + side + back → use back view for symmetry validation.

Q2: Detail level?

• preview — RDP epsilon = 4.0, target ~1–2k tris, < 1 MB GLB.
• production — RDP epsilon = 2.0, target ~5–8k tris, 2–4 MB GLB. Default.
• high — RDP epsilon = 1.0, target ~10–20k tris, may need Decimate to stay under 15 MB.

Q3: Geometry type?

• wires — frames, arms, hinges. Use bevel_depth on curves.
• surfaces — lenses, domes. Use lofted profiles or fill caps.
• hybrid — both. Default for glasses-like objects.

Q4: Real-world scale?

• If the user gave dimensions (e.g., "glasses are 140 mm wide"), use them.
• Otherwise infer from wireframe aspect ratio and assume a sensible default (140 mm width for glasses, 180 mm for helmets, etc.). Confirm with user if not obvious.

Stage 1 — Run the analyzer

Run the bundled analyzer once per view:

python3 ${CLAUDE_SKILL_DIR}/scripts/wireframe_analyzer.py <input.png> <output.json>

The script outputs JSON with this shape:

{
  "metadata": {"image_size": [W, H], "num_contours": N, "parameters": {...}},
  "contours": [[[x, y], ...], ...],
  "bezier_curves": [[[[P0], [P1], [P2], [P3]], ...], ...]
}

Tuning RDP epsilon (only if defaults fail):

• Output has too few/jagged contours → lower epsilon to 1.0–1.5.
• Output has too many noisy points → raise epsilon to 3.0–4.0.
• Pass via --rdp-epsilon (or edit the call in the script).

Read the JSON with Read. Do not pass huge JSON blobs to Blender — extract what you need first.

Stage 2 — Generate Blender code

Build code in small, self-contained chunks (each execute_blender_code call gets a fresh Python namespace; only bpy.data persists between calls). Always re-import what you need.

Pattern: create a Bezier curve from control points

import bpy

# Identify by stable name; bpy.data persists between calls.
name = 'GEO-lens-right'

curve_data = bpy.data.curves.new(name=name, type='CURVE')
curve_data.dimensions = '3D'
curve_data.resolution_u = 16    # tessellation resolution
curve_data.bevel_depth = 0.001  # 1 mm wire thickness (adjust for surfaces)
curve_data.use_fill_caps = True

obj = bpy.data.objects.new(name, curve_data)
bpy.context.collection.objects.link(obj)

# Control points come from the analyzer JSON (px → mm scaling done client-side).
control_points = [(0.0, 0.0, 0.0), (0.5, 1.0, 0.0), (1.5, 1.0, 0.0), (2.0, 0.0, 0.0)]

spline = curve_data.splines.new(type='BEZIER')
spline.bezier_points.add(len(control_points) - 1)
for i, (x, y, z) in enumerate(control_points):
    pt = spline.bezier_points[i]
    pt.co = (x, y, z)
    pt.handle_left_type = 'ALIGNED'   # C¹ smooth
    pt.handle_right_type = 'ALIGNED'

print(f"created:{name}")  # signal back via stdout

Pixel → world conversion (do this in the code you generate, before sending to Blender):

norm_x = px_x / img_width
norm_y = 1.0 - (px_y / img_height)   # flip Y; image origin is top-left
x_world = (norm_x - 0.5) * world_width_mm / 1000.0   # to metres
y_world = (norm_y - 0.5) * world_height_mm / 1000.0

Pattern: convert curves to mesh + cleanup

import bpy

name = 'GEO-lens-right'
obj = bpy.data.objects[name]

bpy.context.view_layer.objects.active = obj
bpy.ops.object.convert(target='MESH')

bpy.ops.object.mode_set(mode='EDIT')
bpy.ops.mesh.remove_doubles(threshold=0.0001)
bpy.ops.mesh.normals_make_consistent(inside=False)
bpy.ops.object.mode_set(mode='OBJECT')
bpy.ops.object.shade_smooth()

mesh = obj.data
print(f"mesh:{name} verts:{len(mesh.vertices)} polys:{len(mesh.polygons)}")

Pattern: PBR material (Principled BSDF — the only shader glTF exports cleanly)

import bpy

mat = bpy.data.materials.get('MAT-frame-metal') or bpy.data.materials.new('MAT-frame-metal')
mat.use_nodes = True
bsdf = mat.node_tree.nodes['Principled BSDF']
bsdf.inputs['Base Color'].default_value = (0.08, 0.08, 0.10, 1.0)
bsdf.inputs['Metallic'].default_value = 1.0
bsdf.inputs['Roughness'].default_value = 0.25

obj = bpy.data.objects['GEO-frame']
if obj.data.materials:
    obj.data.materials[0] = mat
else:
    obj.data.materials.append(mat)
print('material:assigned')

Material presets (use these unless the user specifies):

• MAT-frame-metal — (0.08, 0.08, 0.10) base, metallic=1.0, roughness=0.25 (brushed steel)
• MAT-lens-mirror — (0.05, 0.08, 0.15) base, metallic=0.8, roughness=0.05, IOR=1.5 (mirror glass)
• MAT-pad-silicone — (0.65, 0.63, 0.60) base, metallic=0.0, roughness=0.7 (matte silicone)

Pattern: export to GLB

import bpy, os

filepath = '/tmp/wireframe_output.glb'
bpy.ops.export_scene.gltf(
    filepath=filepath,
    export_format='GLB',
    export_materials='EXPORT',
    export_uv=True,
    export_normals=True,
    export_animations=False,
    export_yup=True,
)
size_mb = os.path.getsize(filepath) / (1024 * 1024)
print(f"export:{filepath} size_mb:{size_mb:.2f}")

If size_mb > 15: apply Decimate and re-export (see error recovery).

Stage 3 — Validate

After the full pipeline, validate before declaring success:

1. mcp__blender__get_scene_info — confirm expected objects exist.
2. For paired parts (left/right lens), call mcp__blender__get_object_info on each and compare bounding box widths. Tolerance: 1 mm.
3. Triangle count: get via get_object_info. If a part exceeds budget, plan Decimate.
4. File size: must be ≤ 15 MB hard cap, ideally ≤ 8 MB.

Error recovery

Symptom	Likely cause	Fix
Code execution error: ... from MCP	Bad Python in generated code	Re-emit code in smaller chunks; trace the line from the error message
Could not connect to Blender	Addon not running	Tell the user to start Blender + addon
Timeout waiting for Blender response	Code chunk too large or slow	Break into smaller execute_blender_code calls
Variables undefined across calls	Each call gets a fresh namespace	Re-import modules; refer to objects by bpy.data.objects['name']
Analyzer outputs 0 contours	Image too low contrast	Re-run with --gaussian-kernel 7 --canny-t1 30
Asymmetric lenses	Original drawing asymmetric, or contour detection inconsistent	Warn the user; do not auto-mirror unless asked
GLB too large	High poly count or embedded textures	Apply DECIMATE modifier with ratio 0.6–0.8; re-export
Mesh has holes	Curve resolution too low	Raise curve_data.resolution_u to 24 or 32; reconvert
Material missing in GLB	Used non-Principled-BSDF nodes	Rebuild material using only Principled BSDF

Decimate code pattern (when GLB > 15 MB)

import bpy

obj = bpy.data.objects['GEO-frame']
bpy.context.view_layer.objects.active = obj

mod = obj.modifiers.new(name='Decimate', type='DECIMATE')
mod.ratio = 0.7
mod.use_collapse_degenerate = True
bpy.ops.object.modifier_apply(modifier=mod.name)
print(f"decimated:{obj.name} verts:{len(obj.data.vertices)}")

Output to user

When done, report:

• Output path of the GLB file
• File size in MB (vs 15 MB cap)
• Triangle count per part (vs 30 000 cap)
• Material slots assigned
• Any warnings (asymmetry, decimation applied, fallbacks used)

Example:

✓ Exported /tmp/wireframe_output.glb (2.4 MB)
Triangles: 5 200 (3 parts: GEO-frame, GEO-lens-right, GEO-lens-left)
Materials: MAT-frame-metal, MAT-lens-mirror
Warnings: none

When to load deeper references

The body above covers the 80% case. For the long tail, load these on demand:

• references/algorithms.md — image-processing pipeline theory (Canny, RDP, least-squares Bezier fitting), 2D-to-3D reconstruction principles, ISO 128 orthographic standards. Load when the analyzer output looks wrong and you need to tune parameters.
• references/blender-patterns.md — exhaustive Blender Python patterns (lofting, surface revolution, custom modifier stacks). Load when the user requests non-standard geometry (curved surfaces, complex bridges, articulated parts).
• references/best-practices.md — performance optimization (foreach_set, batch ops, context caching), naming conventions (Blender Studio standards), modifier stack ordering. Load when builds are slow or output topology is poor.

Constraints

• Blender ≥ 4.0 (5.x preferred). The Principled BSDF node and glTF exporter are stable across these versions.
• glTF embedded only (no .bin + textures sidecar; no KTX2/Draco compression — Three.js needs extra loaders we haven't vendored).
• PNG textures only (max 1024×1024). Prefer flat PBR colours; textures only when essential.
• No bone animations in the GLB. Idle motion is driven in JS by the consumer site.

Tip

If the user just says "convert this wireframe", default to: view_type=auto-detect, detail_level=production, geometry_type=hybrid, world_width_mm=auto. Only ask for clarification if multiple interpretations are plausible.