Scaffold Shader

Scaffold a simple WGSL shader

Generate a minimal, correct WGSL file (plus optional JS wiring) for a mesh rendered through RenderPipeline + Mesh. The base shader is deliberately bare — vs/fs with the standard transform uniforms and a fragment that outputs the normal mapped to 0..1. No custom uniforms, no textures: those are modifications you layer on top after generating, per the task. The reference shape is examples/hellowebgpu/cube.wgsl (same conventions).

Conventions that are NOT optional (reflection-enforced)

These come from webgpu-utils reflection in RenderPipeline/Mesh — get one wrong and the pipeline silently shades garbage or fails construction:

• Uniform block MUST be @group(0) @binding(0) var<uniform> uniforms : Uniforms. Lowercase uniforms, struct typed (commonly Uniforms). RenderPipeline reads this.defs.uniforms.uniforms by that exact name.
• Vertex entry point MUST be vs, fragment MUST be fs. Hardcoded.
• Mesh.draw writes standard uniforms BY NAME into the struct — only the fields that exist are written. Available: projectionMatrix, viewMatrix, modelViewMatrix, modelMatrix, objectMatrix (inverse model), normalMatrix (mat3x3f), cameraPosition (vec3f), cameraQuaternion (vec4f), resolution (vec2f), time (f32). Declare only the subset the shader uses, spelled exactly. Custom uniforms (e.g. uScale, uAlpha) go after them and are set via mesh.uniforms.set({...}) — the Mesh owns the uniform values, not the pipeline.
• Vertex attribute @location is assigned by declaration ORDER in the geometry's data object, not by name. Standard primitives (@core/primitives Box/Sphere/…) emit position (loc 0), normal (loc 1), uv (loc 2). The Vertex struct must match that order.
• Texture uniforms are named t<Name> (e.g. tMap). Samplers keep descriptive names. Only add these if the shader actually samples a texture — a declared binding with no bind-group entry throws at pipeline creation.

Workflow

1. Ask/confirm only what changes the output (skip if obvious from the request):

   • Shader name / target file path (default: alongside the consuming JS, e.g. examples/<name>/<name>.wgsl, or ./<name>.wgsl next to the caller).
   • Does it need the JS pipeline wiring too, or just the .wgsl? Default: just the .wgsl unless they're clearly starting a new example.

2. Generate the base .wgsl by RUNNING the scaffold script — don't hand-write the boilerplate. The script emits a guaranteed-correct vs/fs skeleton with the bindings/struct/attribute order already right, so you spend your effort on the task-specific shading, not on re-deriving reflection rules:

   python .claude/skills/scaffold-shader/scripts/scaffold.py \
     --out examples/<name>/<name>.wgsl \
     # --std projectionMatrix,modelViewMatrix,normalMatrix,time  # override std fields
     # --force                   # overwrite an existing file

   It refuses to clobber an existing file unless --force. Run scaffold.py -h for the full flag list.

3. Layer the requested modifications ON TOP of the generated file with Edit — the script output is a bare starting point (normal→0..1 fragment), not the finished shader. This is where the user's actual intent lands: custom uniforms, textures, custom fragment math, extra varyings, displacement in the vertex stage, sampling logic, etc. Keep the reflection conventions intact while you edit:

   • custom uniforms go AFTER the standard fields in Uniforms, set via mesh.uniforms.set({...});
   • textures are t<Name> + a sampler at the next free @binding, and need a matching bind-group entry (see references/js-wiring.md).

4. Validate the WGSL without a browser — node scripts/validate-shaders.mjs <file> runs naga. The freshly-generated base always passes; run it again after your edits to catch syntax/type errors before the user loads the page. (If naga is absent the script exits 2 — brew install naga-cli, not naga.)

5. If JS wiring requested, write it from references/js-wiring.md (no-texture variant is the short path; texture variant adds the sampler/texture bind-group entries via pipeline.defs.samplers.* / pipeline.defs.textures.*).

6. Tell the user how to render it: new RenderPipeline(gpu, { code, vertexBuffers: geometry.bufferLayouts }) → new Mesh(gpu, { pipeline, geometry, bindGroups }) → mesh.setParent(scene). The Mesh REQUIRES a bindGroups factory (pipeline serves layouts only — see references/js-wiring.md). Custom uniforms set with mesh.uniforms.set({...}) (Mesh.draw uploads each frame).

7. Hot reload works automatically — every *.wgsl?raw import is an HMR boundary, so editing the new file reloads the pipeline live (ShaderReload).