web-animation-design（网页动画设计）

Web Animation Design

⚠️ Creative Pack — NOT auto-apply

This skill is part of the creative pack. Use when the task explicitly involves animation, motion, or interaction feel. Do NOT load this for general UI building — the motion reference in design-review covers baseline motion quality.

Use when: user asks about animations, easing, springs, transitions, interaction feel, or "make it smooth." Skip when: building standard UI where the motion reference in design-review is sufficient.

A comprehensive guide for creating animations that feel right, based on Emil Kowalski's "Animations on the Web" course.

Initial Response

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

I'm ready to help you with animations based on Emil Kowalski's animations.dev course.

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

Review Format (Required)

When reviewing animations, you MUST use a markdown table. Do NOT use a list with "Before:" and "After:" on separate lines. Always output an actual markdown table like this:

Wrong format (never do this):

Before: transform: scale(0)
After: transform: scale(0.95)
────────────────────────────
Before: 400ms duration
After: 200ms

Correct format: A single markdown table with | Before | After | columns, one row per issue.

Decision Tree: What Tool Do I Use?

Does this involve layout changes, shared transitions, or exit animations in React?
├── Yes → Framer Motion (layout animations, AnimatePresence, layoutId)
│         Import from "motion/react" (NOT "framer-motion")
└── No
    ├── Is it a simple enter/exit or hover? → CSS transitions/keyframes
    ├── Is it performance-critical (heavy page, many elements)? → CSS (hardware-accelerated)
    ├── Does it need spring physics or interruptibility? → Framer Motion
    ├── Does it need gesture tracking (drag, cursor follow)? → FM motion values
    └── Is it a constant-speed loop? → CSS keyframes

Always check prefers-reduced-motion. No exceptions.

Quick Start

Every animation decision starts with these questions:

1. Is this element entering or exiting? → Use ease-out
2. Is an on-screen element moving? → Use ease-in-out
3. Is this a hover/color transition? → Use ease
4. Will users see this 100+ times daily? → Don't animate it

The Easing Blueprint

ease-out (Most Common)

Use for user-initiated interactions: dropdowns, modals, tooltips, any element entering or exiting the screen.

/* Sorted weak to strong */
--ease-out-quad: cubic-bezier(0.25, 0.46, 0.45, 0.94);
--ease-out-cubic: cubic-bezier(0.215, 0.61, 0.355, 1);
--ease-out-quart: cubic-bezier(0.165, 0.84, 0.44, 1);
--ease-out-quint: cubic-bezier(0.23, 1, 0.32, 1);
--ease-out-expo: cubic-bezier(0.19, 1, 0.22, 1);
--ease-out-circ: cubic-bezier(0.075, 0.82, 0.165, 1);

Why it works: Acceleration at the start creates an instant, responsive feeling. The element "jumps" toward its destination then settles in.

ease-in-out (For Movement)

Use when elements already on screen need to move or morph. Mimics natural motion like a car accelerating then braking.

/* Sorted weak to strong */
--ease-in-out-quad: cubic-bezier(0.455, 0.03, 0.515, 0.955);
--ease-in-out-cubic: cubic-bezier(0.645, 0.045, 0.355, 1);
--ease-in-out-quart: cubic-bezier(0.77, 0, 0.175, 1);
--ease-in-out-quint: cubic-bezier(0.86, 0, 0.07, 1);
--ease-in-out-expo: cubic-bezier(1, 0, 0, 1);
--ease-in-out-circ: cubic-bezier(0.785, 0.135, 0.15, 0.86);

ease (For Hover Effects)

Use for hover states and color transitions. The asymmetrical curve (faster start, slower end) feels elegant for gentle animations.

transition: background-color 150ms ease;

linear (Avoid in UI)

Only use for:

• Constant-speed animations (marquees, tickers)
• Time visualization (hold-to-delete progress indicators)

Linear feels robotic and unnatural for interactive elements.

ease-in (Almost Never)

Avoid for UI animations. Makes interfaces feel sluggish because the slow start delays visual feedback.

Paired Elements Rule

Elements that animate together must use the same easing and duration. Modal + overlay, tooltip + arrow, drawer + backdrop—if they move as a unit, they should feel like a unit.

/* Both use the same timing */
.modal {
  transition: transform 200ms ease-out;
}
.overlay {
  transition: opacity 200ms ease-out;
}

Timing and Duration

Duration Guidelines

Rules:

• UI animations should stay under 300ms
• Larger elements animate slower than smaller ones
• Exit animations can be ~20% faster than entrance
• Match duration to distance - longer travel = longer duration

The Frequency

Determine how often users will see the animation:

• 100+ times/day → No animation (or drastically reduced)
• Occasional use → Standard animation
• Rare/first-time → Can be more special

Example: Raycast never animates because users open it hundreds of times a day.

When to Animate

Do animate:

• Enter/exit transitions for spatial consistency
• State changes that benefit from visual continuity
• Responses to user actions (feedback)
• Rarely-used interactions where delight adds value

Don't animate:

• Keyboard-initiated actions
• Hover effects on frequently-used elements
• Anything users interact with 100+ times daily
• When speed matters more than smoothness

Marketing vs. Product:

• Marketing: More elaborate, longer durations allowed
• Product: Fast, purposeful, never frivolous

Spring Animations

Springs feel more natural because they don't have fixed durations—they simulate real physics.

When to Use Springs

• Drag interactions with momentum
• Elements that should feel "alive" (Dynamic Island)
• Gestures that can be interrupted mid-animation
• Organic, playful interfaces

Configuration

Apple's approach (recommended):

// Duration + bounce (easier to understand)
{ type: "spring", duration: 0.5, bounce: 0.2 }

Traditional physics:

// Mass, stiffness, damping (more complex)
{ type: "spring", mass: 1, stiffness: 100, damping: 10 }

Bounce Guidelines

• Avoid bounce in most UI contexts
• Use bounce for drag-to-dismiss, playful interactions
• Keep bounce subtle (0.1-0.3) when used

Interruptibility

Springs maintain velocity when interrupted—CSS animations restart from zero. This makes springs ideal for gestures users might change mid-motion.

Layout Animations (Framer Motion)

The most powerful FM feature. Lets you animate properties CSS can't: flex-direction, justify-content, position changes.

The layout Prop

Add layout to any motion.* element to auto-animate layout changes:

<motion.div layout className="element" />

When this element's size or position changes (due to state, content, siblings), FM animates it smoothly. No manual measurement needed.

Shared Layout Animations (layoutId)

Connect two separate elements so one morphs into the other:

// Tab highlight — only rendered for active tab
{activeTab === tab ? (
  <motion.div layoutId="tab-indicator" className="highlight" />
) : null}

Use cases: tab highlights, card → modal expansion, button → popover morph, trash interaction (images move between containers).

Creative trick: layoutId creates illusions. The feedback popover's "placeholder" is actually a <span> with a shared layoutId — not a real textarea placeholder. It morphs from button text to popover text.

Dynamic Height Animation

FM can't animate auto to auto. Use react-use-measure:

import useMeasure from "react-use-measure";
const [ref, bounds] = useMeasure();

<motion.div animate={{ height: bounds.height }}>
  <div ref={ref}>{dynamicContent}</div>
</motion.div>

AnimatePresence (Deep)

Modes

• "sync" (default) — enter and exit play simultaneously
• "wait" — exit completes before enter starts (copy/check icon swap)
• "popLayout" — removes exiting element from layout flow immediately (often the right choice for morphing UIs)

Direction-Aware Transitions

Use the custom prop to pass dynamic data to exiting components (whose state is stale):

<AnimatePresence mode="popLayout" custom={direction}>
  <motion.div
    key={step}
    custom={direction}
    initial="enter"
    animate="center"
    exit="exit"
    variants={{
      enter: (dir) => ({ x: dir > 0 ? 100 : -100, opacity: 0 }),
      center: { x: 0, opacity: 1 },
      exit: (dir) => ({ x: dir > 0 ? -100 : 100, opacity: 0 }),
    }}
  />
</AnimatePresence>

Key Rules

• Always add key prop on animated elements inside AnimatePresence
• Use initial={false} to skip mount animation (icon swaps, button states)
• Known bug: rapid switching can show both elements — pin to FM v11.0.10 if hit

Motion Values & Hooks

Motion values update outside React's render cycle — no re-renders, 60fps.

useMotionValue — Instant updates (gestures)

const x = useMotionValue(0);
// Update via x.set(newValue), read via x.get()
<motion.div style={{ x }} />

Use for: direct gesture tracking (drag distance → scale), any 1:1 mapping where spring lag would feel disconnected.

useSpring — Animated updates (follow-behind)

const x = useSpring(0, { mass: 0.1, damping: 16, stiffness: 71 });
// x.set(newValue) animates to it with spring physics

Use for: cursor followers, momentum effects, anything that should trail behind input.

useTransform — Map one value to another

// Range mapping: y position [0, 300] → scale [1, 1.5]
const scale = useTransform(y, [0, 300], [1, 1.5]);

// Function form: format a value
const display = useTransform(angle, v => `${Math.round(v)}°`);

Use for: scroll-linked effects, cursor-distance effects, value formatting.

useMotionTemplate — String interpolation with motion values

const clipPath = useMotionTemplate`inset(0px ${percent}% 0px 0px)`;
<motion.div style={{ clipPath }} />

MotionConfig — Default transitions for a subtree

<MotionConfig transition={{ type: "spring", duration: 0.5, bounce: 0.2 }}>
  {/* All children use this transition unless overridden */}
</MotionConfig>

Orchestration (Stagger & Sequencing)

Staggered entrance animations create a wave effect. Trial and error until it feels right — no formula.

CSS stagger (no library):

.item { animation: fadeSlideIn 400ms ease-out both; }
.item:nth-child(1) { animation-delay: 0ms; }
.item:nth-child(2) { animation-delay: 50ms; }
.item:nth-child(3) { animation-delay: 100ms; }
/* etc. */

FM stagger:

const container = {
  animate: { transition: { staggerChildren: 0.05 } }
};
const item = {
  initial: { opacity: 0, y: 20 },
  animate: { opacity: 1, y: 0 }
};

Rules:

• Keep delays small (30-80ms between items)
• Cap total sequence time — 10 items at 80ms each = 800ms, too slow
• Marketing pages can be more elaborate; product UI should be fast

Brand Expression Through Animation Speed

Animation timing IS brand identity:

• Speed brand (Vercel): instant or very fast, minimal easing. "We don't waste your time."
• Premium brand (Stripe): slower, more deliberate. ease curve (not ease-out) for elegance.
• Playful brand (Family): springs with subtle bounce, fluid morphing.
• Product UI should generally feel fast regardless of brand.
• Marketing pages are where you express brand personality through motion.

Fluid Interfaces (Aspirational)

The north star: nothing "appears" or "disappears" — everything morphs. Family (iOS) is the gold standard.

• Shared layout animations are the web's closest tool to native fluidity
• Fluid motion improves perceived performance (feels faster even with same load time)
• Think about animations BEFORE designing the UI — position elements to enable seamless transitions
• Currently hard on web, but the direction everything is heading
• Text morphing (e.g., button label changes) highlights state changes subtly

Performance

The Golden Rule

Only animate transform and opacity. These skip layout and paint stages, running entirely on the GPU.

Avoid animating:

• padding, margin, height, width (trigger layout)
• blur filters above 20px (expensive, especially Safari)
• CSS variables in deep component trees

Optimization Techniques

/* Force GPU acceleration */
.animated-element {
  will-change: transform;
}

React-specific:

• Animate outside React's render cycle when possible
• Use refs to update styles directly instead of state
• Re-renders on every frame = dropped frames

Framer Motion:

// Hardware accelerated (transform as string)
<motion.div animate={{ transform: "translateX(100px)" }} />

// NOT hardware accelerated (more readable)
<motion.div animate={{ x: 100 }} />

CSS vs. JavaScript

• CSS animations run off main thread (smoother under load)
• JS animations (Framer Motion, React Spring) use requestAnimationFrame
• CSS better for simple, predetermined animations
• JS better for dynamic, interruptible animations
• Combine both: CSS for simple/perf-critical animations, FM for complex/layout/springs

CSS Variables Gotcha

CSS variables are inheritable — changing one causes style recalc for ALL children. In deep component trees (20+ items), this kills drag/scroll performance.

// BAD — recalculates all children
const style = { "--swipe-amount": `${distance}px` };

// GOOD — updates only this element
const style = { transform: `translateY(${distance}px)` };

Transform Shift Fix

GPU/CPU handoff can cause 1px shift at animation start/end:

.element { will-change: transform; }

Accessibility

Animations can cause motion sickness or distraction for some users.

prefers-reduced-motion

Whenever you add an animation, also add a media query to disable it:

.modal {
  animation: fadeIn 200ms ease-out;
}

@media (prefers-reduced-motion: reduce) {
  .modal {
    animation: none;
  }
}

Reduced Motion Guidelines

Reduced motion ≠ no motion. Animations help users understand UI. Removing all motion hurts comprehension.

• Remove: transform-based movement, scaling, sliding, parallax
• Keep: opacity fades, color transitions, background changes
• Replace: slide-in → fade-in, scale → opacity, complex → simple
• Disable autoplay on videos/animated images; show play buttons instead
• For looping hero animations: pause on a good frame via animation-delay: -0.4s

Framer Motion Implementation

Option 1: Per-component hook

import { useReducedMotion } from "motion/react";

function Component() {
  const shouldReduceMotion = useReducedMotion();
  const closedX = shouldReduceMotion ? 0 : "-100%";

  return (
    <motion.div animate={{
      opacity: isOpen ? 1 : 0,
      x: isOpen ? 0 : closedX
    }} />
  );
}

Option 2: App-wide wrapper (recommended)

import { MotionConfig } from "motion/react";

// Wraps your entire app — FM auto-reduces to opacity/backgroundColor only
<MotionConfig reducedMotion="user">{children}</MotionConfig>

Note: default is "never" — you must set this yourself.

Touch Device Considerations

/* Disable hover animations on touch devices */
@media (hover: hover) and (pointer: fine) {
  .element:hover {
    transform: scale(1.05);
  }
}

Touch devices trigger hover on tap, causing false positives.

Practical Tips

Quick reference for common scenarios. See PRACTICAL-TIPS.md for detailed implementations.

Easing Decision Flowchart

Is the element entering or exiting the viewport? ├── Yes → ease-out └── No ├── Is it moving/morphing on screen? │ └── Yes → ease-in-out └── Is it a hover change? ├── Yes → ease └── Is it constant motion? ├── Yes → linear └── Default → ease-out

Reference Files

• PRACTICAL-TIPS.md - Detailed implementations for common animation scenarios