# Depth field · Light and distance

Independent observation study. Domain: website consumer / Motion and Design Engineering. This is an unaffiliated learning example.

A deterministic point projection links size and trace length to depth. A stationary frame is useful before playback, and the same phase can be revisited with a native range control.

## Observation and original-source boundary

Observed public listing: [ATC shader](https://21st.dev/@xordev/components/atc-shader). Observed demo URL: https://cdn.21st.dev/larsen66/atc-shader/default/bundle.1756885507225.html.

The two ATC frames show a dark field of bright points and traces with different positions after time elapsed. They do not establish the original formula, exact speed, easing, loop length or input response.

Original source acquired: false. Original source acquisition status: unresolved. The supplied Stage 3 record says: 원래 게시자 license 빈값; 정확한 ATC 구현의 재사용 허락 미확인. That status is preserved, not re-investigated or replaced by this implementation's license.

The projection formula, green-and-amber palette, editorial lettering, initial still frame, frame slider, trail switch, pause control and reduced-motion policy are independently authored learning features.

The new copy, artwork, code and documentation are covered by the bundled MIT notice. No original source file, asset, distinctive copy, screenshot or brand is included. The evidence revision does not grant a license for the observed original.

## Evidence identity

sourceRevision: 0443ba9dca9ebd8fb0155c7370a07074c5366ed5939fc380a3e77d30fd5fc86c

The revision is SHA-256 of the JSON sourceEvidence object in the manifest. It binds the complete Stage 3 index and SceneBook hashes, this record's observation, and its named PNG and metadata hashes. It identifies actual research evidence, not an original Git checkout or a runtime result.

- Stage 3 index: artifacts/full-import/21st-author-sources/stage3/index.json, SHA-256 a9bd0da9712ea0a24e26b3612bfc87a09e13ee5cbb318eb97fe375d8c18d8c08.
- SceneBook: artifacts/full-import/21st-author-sources/stage3/SCENEBOOK.md, SHA-256 140b65a2248332fd415c9a4f42879cc060004f290ea83232af68558f2011e564.
- Relevant frame names: atc-initial, atc-later.

The initial PNG for this record was directly viewed during implementation as explicitly requested. Other states follow the Stage 3 transcription; their bytes and metadata hashes were checked, not claimed as newly observed interactions.

## Running and editing

Open index.html directly. The page contains its CSS, JavaScript and original SVG artwork and makes no outside requests. A content-security policy restricts runtime content to inline script/styles and data/blob images. There is no browser storage or remote write.

[styles.css](styles.css) and [script.js](script.js) are exact reference copies of the inline code. To edit a downloaded page, change its inline code or create your own build step. Editing only those companion copies does not change index.html. For repository generation, use StyleGallery/site as the working directory. The authoring modules are vendor/21st-studies/scenes.mjs and models.mjs; run node scripts/build-21st-studies.mjs there. Canonical Markdown lives in the parent StyleGallery checkout, so a binding such as motion/accessible-motion.md resolves as ../motion/accessible-motion.md from the site directory. Generation needs that parent corpus and the private research packet; running the download does not. A rebuild overwrites generated files.

Initial state: phase 0.36; playback stopped; traces shown; system reduced-motion preference applied during initialization.

## Interaction and sizing contract

The initial composition targets 640 × 420 CSS pixels. The field starts stationary; Play is explicit, a preference change stops it, and leaving the document pauses it without automatic resume. A native frame slider retains inspection without playback. At 320 pixels the controls wrap and the document owns scrolling. No horizontal pan or wheel interception is used. These are implementation contracts to check in the rendered page, not conformance results.

## Verification boundary

The generator verifies evidence bytes against recorded hashes, three-ID membership, unresolved source status, canonical Markdown anchors and hashes, named authored functions, JavaScript parsing, semantic landmarks, ID/label relationships, inline-copy equality, and forbidden runtime destinations/storage. This record's model checks cover finite projection, playback-to-pause frame revisit at matching tenth-percent precision, and preference invariants. These are source/model checks, not rendered interaction checks.

[KNOWLEDGE.json](KNOWLEDGE.json) holds actionable checks with status not_executed. runtime_verified: false. Browser interaction, full keyboard paths, screen-reader output, comfort and performance remain unverified. In the site checkout, research/full-import/preview-posters.md is the central SG initial-render report, artifacts/full-import/preview-posters/index.json owns capture receipts, and artifacts/full-import/preview-posters/visual-review.json owns frame observations. These private reports are not bundled in the download. Initial-render evidence does not change the interaction boundary.

consumer_reference: consumer-reference/agent-native/registry.json