--- name: css-animations description: CSS animation adapter patterns for HyperFrames. Use when authoring CSS keyframes, animation-delay based timing, animation-fill-mode, animation-play-state, or CSS-only motion that HyperFrames must seek deterministically during preview and rendering. --- # CSS Animations for HyperFrames HyperFrames can seek CSS keyframe animations through its `css` runtime adapter. Use this for simple repeated motifs, background motion, shimmer, glow, masks, and non-sequenced decoration. For scene choreography, GSAP is usually clearer. CSS animations work best when the motion belongs to one element and has a fixed duration. ## Contract - Put the animated element in the DOM before runtime initialization finishes. - Give timed elements a `data-start` value so local animation time matches the clip. - Use finite `animation-duration` and `animation-iteration-count` because the negative-delay fallback cannot represent unbounded duration in environments without WAAPI-backed CSS animations. - Prefer `animation-fill-mode: both` so seeked states hold before and after active motion. - Avoid wall-clock JavaScript, hover-triggered state, and class toggles that depend on user events. The adapter discovers elements with computed `animation-name`, seeks their browser `Animation` handles when available, and falls back to pausing with negative `animation-delay`. ## Basic Pattern ```html

``` ## Stagger Pattern Use CSS custom properties to avoid duplicating keyframes: ```html

``` ## Good Uses - Decorative loops with a known repeat count. - Mask, glow, shimmer, grain, and subtle parallax layers. - Simple one-element entrances where a full JS timeline would be excessive. ## Avoid - Infinite CSS animations unless you have verified the browser exposes seekable WAAPI-backed CSS animation handles. Prefer a finite iteration count covering the visible duration. - Animating layout properties like `top`, `left`, `width`, or `height` when transforms work. - Relying on hover, focus, scroll, or media queries to trigger render-critical motion. - Changing animation classes after startup unless another deterministic timeline controls that change. ## Validation After editing CSS animation compositions: ```bash npx hyperframes lint npx hyperframes validate ``` ## Credits And References - HyperFrames adapter source: `packages/core/src/runtime/adapters/css.ts`. - MDN CSS animation documentation: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/animation - MDN `animation-fill-mode`: https://developer.mozilla.org/en-US/docs/Web/CSS/animation-fill-mode

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