Blender NPR Cycles

Create a Cycles-compatible object-outline mask with Blender 5.2's Shader Raycast node. This is a shader workflow, not Geometry Nodes.

Suite Authority

Follow ../blender-production-router/references/production-protocol.md and ../blender-production-router/references/native-component-contract.md. The Router owns route, stage, budgets, rollback, and pauses. This skill owns Cycles raycast shading and outline evidence only; it cannot reroute, restart analysis, or use NPR to conceal geometry defects.

System Choice And Asset Boundary

Read ../blender-production-router/references/system-choice-contract.md. A requested stylized, shader, or compositor candidate may be discovered by blender-local-asset-library, but this Skill owns whether it is compatible with Cycles and the four-raycast outline method. Do not import an Eevee-only Shader to RGB graph or a Geometry Nodes outline merely because it comes from a local asset library.

Require passed formal topology, Structural Forms, Transition Forms, connection, silhouette, and real-bevel gates first. Raycast outlines may stylize an accepted surface; they are not evidence of a valid contour, welded shell, manufactured radius, or clean intersection.

Availability Gate

• Require Blender 5.2 or newer.
• Require Cycles and ShaderNodeRaycast.
• Never substitute Eevee-only Shader to RGB.
• If the Blender version lacks Shader Raycast, route to inverted hull, Line Art, Freestyle, or compositor line extraction and record the fallback.

Raycast Method

For each camera-plane offset +X, -X, +Y, and -Y:

1. Transform the offset vector from Camera space to World space.
2. Scale it by the requested outline width.
3. Add it to Geometry Position to create the ray origin.
4. Multiply Geometry Incoming by -1 to point toward the camera.
5. Run Shader Raycast with a bounded ray length.
6. Read Is Hit.

Multiply the four hit masks. A point that remains covered in all four shifted tests is interior; a point that fails at least one test becomes outline. Use the result to mix a dark outline shader with a Cycles-compatible base shader.

Use scripts/build_cycles_npr.py to build:

• one reusable ray-sample shader group;
• one four-direction outline-and-toon shader group;
• one owned material on explicitly selected mesh objects.

The script defaults to local-object ray tests so nearby objects do not contaminate the silhouette. Scene-aware ray tests must be an intentional choice.

Hard Rules

• Do not reset the scene or World.
• Do not replace an existing user material without explicit approval.
• Do not use Shader to RGB in Cycles.
• Do not implement this method as Geometry Nodes.
• Do not use unlimited ray distance or an unbounded width.
• Do not assume world-space width is screen-space constant. Test near and far cameras.
• Do not silently enable scene-aware ray tests; neighboring geometry can create false outlines.
• Account for four additional shader-ray queries per shaded point when setting render samples, subdivision, and resolution.
• Disable the outline and verify neutral clay plus wireframe before accepting the NPR result.

Validation Gate

Check all of the following:

• Cycles is active and Blender is at least 5.2.
• The sample group contains Camera-to-World vector transform, scaled offset, shifted position, reversed Incoming direction, and Shader Raycast.
• The look group contains exactly four ray-sample instances with +X/-X/+Y/-Y offsets.
• Three multiply operations combine all four Is Hit values.
• Local-only behavior matches the requested interaction policy.
• Front, profile, three-quarter, near, and far renders show a coherent outline.
• Neighboring-object, concavity, thin-part, transparency, displacement, and animation tests have been reviewed.
• Render cost and unique review-image paths are reported.

Read references/cycles-raycast-outline.md for the reconstructed graph, limitations, fallbacks, and official Blender documentation.