apple-design

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---
name: apple-design
description: Apple's approach to interface design and fluid, physical motion, translated for the web. Use when building or reviewing gesture-driven UI, spring animations, drag/swipe/sheet interactions, momentum and interruptible transitions, translucent materials and depth, typography (optical sizing, tracking, leading), reduced-motion, or the design foundations (feedback, spatial consistency, restraint) behind Apple-style interfaces.
---

# Apple Design

## Initial Response

When this skill is first invoked without a specific question, respond only with:

> I'm ready to help you build fluid, Apple-style interfaces on the web, my knowledge comes from Apple's WWDC design talks, translated for the web.

Do not provide any other information until the user asks a question.

How Apple builds interfaces that stop feeling like a computer and start feeling like an extension of you. This knowledge comes from Apple's WWDC design talks — chiefly *Designing Fluid Interfaces* (WWDC 2018) — distilled and translated into the web platform (CSS, Pointer Events, `requestAnimationFrame`, spring libraries like Motion/Framer Motion).

The through-line: **an interface feels alive when motion starts from the current on-screen value, inherits the user's velocity, projects momentum forward, and can be grabbed and reversed at any instant.** Springs are the tool that makes all of this natural, because they are inherently interruptible and velocity-aware.

## The Core Idea

> "When we align the interface to the way we think and move, something magical happens — it stops feeling like a computer and starts feeling like a seamless extension of us."

An interface is fluid when it behaves like the physical world: things respond instantly, move continuously, carry momentum, resist at boundaries, and can be redirected mid-motion. Everything below is a way to get closer to that.

Apple frames design as serving four human needs: **safety/predictability, understanding, achievement, and joy.** Every rule here serves one of them.

## 1. Response — kill latency

The moment lag appears, the feeling of directness "falls off a cliff." Response is the foundation everything else is built on.

- **Respond on pointer-down, not on release.** Highlight a button the instant it's pressed. Waiting for `click`/touch-up to show feedback feels dead.
- **Be vigilant about every latency.** Audit debounces, artificial timers, transition waits, and the ~300ms tap delay. Anything on the input path that isn't essential is a regression.
- **Feedback must be continuous *during* the interaction, not just at the end.** For a drag, slider, or drawer, update the UI 1:1 with the pointer the whole way through — never animate only when the gesture completes.

```css
/* Feedback lives on the press, and it's instant */
.button:active {
  transform: scale(0.97);
  transition: transform 100ms ease-out;
}
```

## 2. Direct manipulation — 1:1 tracking

> "Touch and content should move together."

When the user drags something, it must stay glued to the finger — and respect the offset from *where they grabbed it*. Snapping to the element's center on grab breaks the illusion immediately.

- Use Pointer Events with `setPointerCapture` so tracking continues even when the pointer leaves the element's bounds.
- Track a short **velocity/position history** (last few `pointermove` events), not just the current point — you'll need velocity at release.

```js
el.addEventListener('pointerdown', (e) => {
  el.setPointerCapture(e.pointerId);
  const grabOffset = e.clientY - el.getBoundingClientRect().top; // respect where they grabbed
  // ...track position + timestamp history for velocity
});
```

## 3. Interruptibility — the single most important principle

> "The thought and the gesture happen in parallel."

Every animation must be interruptible and redirectable at any moment. A user must be able to grab a moving element mid-flight and reverse it without waiting for the animation to finish.