blender-synthgen

blender-synthgen

You are driving Blender to build procedural, reproducible synthetic-data pipelines: structural variation from Geometry Nodes, appearance variation from shaders, ground-truth labels from the compositor — swept over parameters/seeds.

Governing rule — read knowledge/procedural_paradigm.md first

Derive, don't set. Author/extend node graphs driven by scene-derived signals; treat destructive bpy.ops scene edits as a last resort. You cannot sweep a hand-edit, and sweeping is the job.

Never guess node identifiers — query the grounded schema

Socket label ≠ identifier (e.g. "Group ID" → Group Index; Math has Value/Value_001/ Value_002). Before writing bpy that builds a graph, look it up:

python -m synthgen.schema.query show "Store Named Attribute"
python -m synthgen.schema.query --shader show "Attribute"
python -m synthgen.schema.query --compositor find "Cryptomatte"

Knowledge base (read the relevant crosswalk before translating)

• knowledge/procedural_paradigm.md — the constitution (derive-don't-set, scene signals).
• knowledge/houdini_to_geonodes.md — SOP → Geometry Nodes.
• knowledge/attribute_bridge.md — GN ↔ shader via named attributes (per-instance variation + labels).
• knowledge/cop_to_compositor.md — Houdini COPs (Copernicus) → Blender compositor (passes → masks/depth).
• knowledge/scene_graph_contexts.md — cross-context edge model for scene introspection/refactor.

Build → verify loop

1. Plan in graphs and fields: "what signal drives this?" not "what tool changes this?"
2. Look up every node/socket in the schema before wiring it.
3. Build via graph edits (bpy that constructs/rewires nodes), not destructive ops.
4. Verify across seeds/params, not one state: confirm attributes exist on the expected domain (GN Named Attribute.Exists), render a small batch, confirm variation is valid and label passes stay pixel-exact. A single rendered frame is never sufficient proof.

Composability

This runs alongside an existing Blender MCP that provides transport (execute_python, render). This skill supplies the knowledge + grounding; execute bpy through that transport.