Shader Extract

Capture one GPU-rendered surface and rebuild it as a verified, runnable local effect module. The governing principle — inherited from the vendored engine this skill wraps — is evidence before implementation: capture what the page's GPU pipeline actually does (shaders, uniforms, pass order, textures, timing) and match it, rather than eyeballing the visual and hand-tuning a lookalike. A lookalike drifts; a capture-matched baseline is faithful and honest about its gaps.

This skill = intake adapter + a vendored evidence-gated engine

The heavy machinery lives in vendor/web-shader-extractor/ — an evidence-gated state machine (surface lock → source/runtime trace → capture → verified baseline → projectize) by lixiaolin94 (MIT; see ATTRIBUTION.md). Do not reimplement it. This wrapper does two things the vendored engine assumes were done elsewhere:

1. Intake — accept a pre-locked surface from the clone-site coordinator so you skip straight to capture instead of re-scouting the whole page.
2. Capture backends — make the concrete, research-verified capture tools explicit (references/capture-backends.md): Spector.js for WebGL1/2 and WebGPU Inspector for WebGPU. These are what actually recover a frame; the vendored policy files describe the discipline, these describe the tools.

Router: how you were invoked

Driven by clone-site (common): you receive a locked surface — selector, bounding box, guessed driver (three.js / unicorn-studio / spline / regl / raw WebGL), and an output dir like output/<host>/effects/<surface-id>/. The surface is already attributed, so skip scouting. Go straight to:

1. Read vendor/web-shader-extractor/SKILL.md and its references/replay-policy.md — that is the operating manual for capture → baseline → projectize.
2. Pick the capture backend by surface type (references/capture-backends.md): WEBGL1/2 → Spector.js; WEBGPU → WebGPU Inspector.
3. Run the vendored state flow from CAPTURE_MINIMUM_TRUTH onward, writing evidence and the baseline into the given output dir.
4. Return a mount-contract module (see below) plus the honesty label.

Standalone (user hands you a URL): you must lock the surface first. Run the full vendored flow from INTAKE (read vendor/web-shader-extractor/SKILL.md). The clone-site script scripts/surface-map.js is a fast way to enumerate and classify canvases if you want a head start, but the vendored TARGET_LOCK gate is authoritative.

Non-negotiables (carried from the vendored engine)

• Honest labels. Every implementation-critical fact is SOURCE, PARTIAL, or GUESS; unlabeled = GUESS. The final module carries a fidelity verdict. Never quietly upgrade a BEHAVIOR_REBUILD (lookalike) to sound like a source replay.
• No compensation tuning. Don't nudge brightness, speed, offsets, noise scale, or color to mask missing pipeline evidence. A visible gap gets recorded in known-gaps.md, not fudged away.
• Baseline before projectize. Get a faithful, verified capture-baseline running first; only then refactor it into an editable module. Don't overwrite a verified baseline for cleanup.
• Cross-origin honesty. If the canvas is cross-origin/tainted and pixel or shader readback is blocked, say so and fall back to a captured poster frame — don't invent a shader you couldn't read.

Output contract (so clone-site can mount it)

Beyond the vendored output/ layout (capture-baseline, editable-project, qa-report, known-gaps), expose the effect through the mount lifecycle the coordinator composites against:

export function mount(canvasEl, opts) { /* start renderer + rAF loop */ return handle }
export function unmount(handle)        { /* cancel rAF, loseContext, free GPU */ }
export function resize(handle, w, h, dpr) { /* resize drawing buffer + viewport */ }

Also emit a poster frame (a captured still) as a fallback for reduced-motion and for the case where reconstruction only reached poster fidelity. Report the fidelity label so the coordinator carries it into the final clone report unchanged.

Where to read next

• references/capture-backends.md — Spector.js (WebGL) and WebGPU Inspector (WebGPU): what each captures, how to drive it, what's reliable vs guesswork.
• vendor/web-shader-extractor/SKILL.md — the full state machine + reference router (surface discovery, target lock, evidence policy, replay policy, QA, Three.js/TSL reconstruction, Unicorn Studio / shaders.com adapters).
• ATTRIBUTION.md — upstream authorship and MIT license.