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https://github.com/heygen-com/hyperframes.git
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Miguel Ángel
bdd0084c2a
* docs: clarify root composition duration is compile-time, not script/--variables parameterizable * chore: regenerate skills-manifest for hyperframes-core docs change
58 lines
5.5 KiB
Markdown
58 lines
5.5 KiB
Markdown
# Determinism, Animation Runtime, and Layout
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HyperFrames seeks compositions frame-by-frame. Every frame must be reproducible from its time value alone — same input time → same pixels. Three contracts enforce this: the **animation runtime contract**, the **determinism rules**, and the **layout contract**.
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## Animation Runtime Contract
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GSAP is the primary runtime. The core requirement is generic: animation state must be seekable from HyperFrames time.
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For GSAP:
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- Create the timeline **synchronously** during page initialization.
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- Use `gsap.timeline({ paused: true })`.
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- Register it on `window.__timelines["<composition-id>"]`.
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- The key must match `data-composition-id` on the composition root.
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- **Do not** call `tl.play()` for render-critical motion.
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- **Do not** build timelines inside `async`, `Promise`, `setTimeout`, or event handlers — the renderer can sample before they finish.
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- **Do not** create empty tweens only to set duration; use `data-duration` on the clip instead.
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- **Do not** `gsap.set()` clip elements from later scenes — they are not in the DOM at page load. Use `tl.set(selector, vars, time)` inside the timeline at or after the clip's `data-start`.
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Use the `hyperframes-animation` skill for tween syntax, position parameters, eases, and performance rules.
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## Determinism Rules
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Rendered frames must be reproducible from the requested time. Do **not** use any of the following for visual state:
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- `Date.now()`, `performance.now()`, or any render-time clock.
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- Unseeded `Math.random()`. Use a seeded PRNG if random-looking placement is needed.
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- Render-time network fetches for required assets. Inline or pre-bundle them.
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- Hover, scroll, pointer, or focus state. The renderer has no input events.
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- Infinite loops such as `repeat: -1`. Compute a finite count: `repeat: Math.max(0, Math.floor(duration / cycleDuration) - 1)` — **`floor`, not `ceil`** (`ceil` overshoots `data-duration` and trips the `gsap_repeat_ceil_overshoot` lint; `max(0, …)` avoids a negative repeat = infinite).
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Also avoid:
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- Animating anything outside the visual-property allowlist: `opacity`, `x`, `y`, `scale`, `rotation`, `color`, `backgroundColor`, `borderRadius`, transforms. Never animate `display` or `visibility` — use opacity/transforms and timed clip visibility instead.
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- Animating the same property on the same element from multiple timelines at the same time — GSAP's overwrite behavior is order-dependent and can flip between renders.
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## Layout Contract
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Build the visible end-state in static HTML and CSS first, then animate from/to that state.
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- The composition root has fixed pixel frame dimensions.
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- **The root composition's total duration (render length / frame count) is fixed at compile time**, read once from the static root `data-duration` before scripts run, like `data-width` / `data-height`. A script or `--variables` value that rewrites the root `data-duration` afterward is ignored. To vary render length per output, author the root `data-duration` directly. (A _clip's_ own `data-duration` is re-read from the live DOM, so scripts/variables can still drive clip lengths. Only when the root omits `data-duration` does the renderer probe the live DOM / timeline for total length.)
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- Scene containers should fill the scene with `width: 100%; height: 100%; box-sizing: border-box`.
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- Use padding, flex, grid, and `max-width` for layout. Avoid positioning main content with hardcoded `top`/`left` offsets when a layout container can do it.
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- Use `position: absolute` for layers and decorative elements, not as the default content-layout strategy.
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- Prefer transforms and opacity for animation.
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- Keep text inside its intended container. For dynamic text, use `max-width`, wrapping, or `window.__hyperframes.fitTextFontSize(text, { maxWidth, fontFamily, fontWeight })`.
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- For text measurement without DOM reflow, use `window.__hyperframes.pretext`: `pretext.prepare(text, font)` then `pretext.layout(prepared, maxWidth, lineHeight)`. Pure arithmetic, ~0.0002 ms per call — safe for per-frame text reflow, shrinkwrap containers, and computing layout before render. `fitTextFontSize` is built on it.
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- **Do not** use `<br>` in body text. Forced breaks ignore the actual rendered font width and produce an extra break when the line already wraps naturally, causing overlap. Let text wrap via `max-width`. Exception: short display titles where each word is deliberately on its own line.
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- **Transformed elements must be block-level + sized.** `transform`/`scaleX`/`scaleY` is a no-op on an inline `<span>`, and scaling an auto-width (0px) element shows nothing → invisible bars/fills. Give them `display: block`/`inline-block`/flex-item **and** a real `width`/`height` (e.g. `width: 100%` inside a sized parent). _(silent — lint/inspect miss it.)_
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- **Absolutely-positioned decoratives that pulse or overshoot** (`yoyo` scale, `back.out`) need clearance at their **peak** size and must not straddle an `overflow: hidden` edge — else they overlap a neighbor or get clipped. Position for the largest frame, not the resting one. _(silent.)_
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## Why This Matters
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The renderer takes a time value and produces a pixel buffer. There is no notion of "playback" — every frame is a fresh seek. Any state that depends on having reached this frame _through_ a prior frame (timers, accumulated state, event-driven animations) will desync when the renderer samples out of order or in parallel.
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If you find yourself reaching for `setTimeout`, `requestAnimationFrame`, or `addEventListener` to drive a visual, rebuild it as a tween on the timeline instead.
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