Marcos Paulo
80 lines
2.4 KiB
Markdown
80 lines
2.4 KiB
Markdown
---
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name: motion
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description:
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Add or review animation on the ai-for-dummies site — transitions, state
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changes, view transitions. Use when any element moves, fades, or transforms,
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or when auditing existing motion for performance and reduced-motion support.
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---
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# Motion
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This is an editorial-print design. Motion is punctuation. Read
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[`../../rules/animation.md`](../../rules/animation.md) — it is binding; this is
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the procedure.
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## Decide it should move
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Answer out loud: **what does this motion tell the user that the static state
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does not?** Valid answers: something changed, attention needs directing to what
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changed, a layout shift needs smoothing. "It feels more polished" is not an
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answer — on this design it reads as generic.
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If there is no answer, ship it static. That is a legitimate, common outcome.
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## Build it
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```css
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.panel {
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transition:
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opacity 180ms cubic-bezier(0.2, 0, 0, 1),
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transform 180ms cubic-bezier(0.2, 0, 0, 1);
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}
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.panel[data-state='entering'] {
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opacity: 0;
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transform: translateY(6px);
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}
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```
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- **`transform` and `opacity` only.** Animating `width`/`height`/`top`/`left`
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forces layout every frame and shows up as a failed INP (budget: 200ms).
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- 150–250ms for UI feedback; up to 400ms for a page transition.
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- One thing moves at a time. No staggered card cascades.
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- `will-change` only immediately before animating, removed after.
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- No animation library. This site's thesis is having no runtime dependencies.
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## Reduced motion is not optional
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```css
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@media (prefers-reduced-motion: reduce) {
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* {
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animation-duration: 0.01ms !important;
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animation-iteration-count: 1 !important;
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transition-duration: 0.01ms !important;
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scroll-behavior: auto !important;
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}
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}
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```
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Then **test it**: DevTools → Rendering → Emulate
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`prefers-reduced-motion: reduce`. The end state must still be correct and the UI
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still usable. Reduced, not broken.
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## Page transitions
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Astro's `<ClientRouter />` is the only sanctioned motion dependency. Before
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enabling it, verify:
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- JS disabled → full navigation still works
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- browser back/forward still works
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- the review desk's query-param deep links survive
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- `prefers-reduced-motion` is honoured
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## Audit an existing animation
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```bash
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grep -rn "transition\|animation\|@keyframes\|transform" src/ --include="*.astro" --include="*.css"
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```
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For each hit ask: does it animate a layout property? does it respect reduced
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motion? is there a stated purpose? Three questions, three possible fixes.
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