Scroll Experience

## Scroll Animation Stack

### Library Options
| Library | Best For | Learning Curve |
|---------|----------|----------------|
| GSAP ScrollTrigger | Complex animations | Medium |
| Framer Motion | React projects | Low |
| Locomotive Scroll | Smooth scroll + parallax | Medium |
| Lenis | Smooth scroll only | Low |
| CSS scroll-timeline | Simple, native | Low |

### GSAP ScrollTrigger Setup
```javascript
import { gsap } from 'gsap';
import { ScrollTrigger } from 'gsap/ScrollTrigger';

gsap.registerPlugin(ScrollTrigger);

// Basic scroll animation
gsap.to('.element', {
  scrollTrigger: {
    trigger: '.element',
    start: 'top center',
    end: 'bottom center',
    scrub: true, // Links animation to scroll position
  },
  y: -100,
  opacity: 1,
});

import { motion, useScroll, useTransform } from 'framer-motion';

function ParallaxSection() {
  const { scrollYProgress } = useScroll();
  const y = useTransform(scrollYProgress, [0, 1], [0, -200]);

  return (
    <motion.div style={{ y }}>
      Content moves with scroll
    </motion.div>
  );
}

@keyframes reveal {
  from { opacity: 0; transform: translateY(50px); }
  to { opacity: 1; transform: translateY(0); }
}

.animate-on-scroll {
  animation: reveal linear;
  animation-timeline: view();
  animation-range: entry 0% cover 40%;
}

### Parallax Storytelling

Tell stories through scroll depth

**When to use**: When creating narrative experiences

```javascript
## Parallax Storytelling

### Layer Speeds
| Layer | Speed | Effect |
|-------|-------|--------|
| Background | 0.2x | Far away, slow |
| Midground | 0.5x | Middle depth |
| Foreground | 1.0x | Normal scroll |
| Content | 1.0x | Readable |
| Floating elements | 1.2x | Pop forward |

### Creating Depth
```javascript
// GSAP parallax layers
gsap.to('.background', {
  scrollTrigger: {
    scrub: true
  },
  y: '-20%', // Moves slower
});

gsap.to('.foreground', {
  scrollTrigger: {
    scrub: true
  },
  y: '-50%', // Moves faster
});

Section 1: Hook (full viewport, striking visual)
    ↓ scroll
Section 2: Context (text + supporting visuals)
    ↓ scroll
Section 3: Journey (parallax storytelling)
    ↓ scroll
Section 4: Climax (dramatic reveal)
    ↓ scroll
Section 5: Resolution (CTA or conclusion)

### Sticky Sections

Pin elements while scrolling through content

**When to use**: When content should stay visible during scroll

```javascript
## Sticky Sections

### CSS Sticky
```css
.sticky-container {
  height: 300vh; /* Space for scrolling */
}

.sticky-element {
  position: sticky;
  top: 0;
  height: 100vh;
}

gsap.to('.content', {
  scrollTrigger: {
    trigger: '.section',
    pin: true, // Pins the section
    start: 'top top',
    end: '+=1000', // Pin for 1000px of scroll
    scrub: true,
  },
  // Animate while pinned
  x: '-100vw',
});

const sections = gsap.utils.toArray('.panel');

gsap.to(sections, {
  xPercent: -100 * (sections.length - 1),
  ease: 'none',
  scrollTrigger: {
    trigger: '.horizontal-container',
    pin: true,
    scrub: 1,
    end: () => '+=' + document.querySelector('.horizontal-container').offsetWidth,
  },
});

## Anti-Patterns

### ❌ Scroll Hijacking

**Why bad**: Users hate losing scroll control.
Accessibility nightmare.
Breaks back button expectations.
Frustrating on mobile.

**Instead**: Enhance scroll, don't replace it.
Keep natural scroll speed.
Use scrub animations.
Allow users to scroll normally.

### ❌ Animation Overload

**Why bad**: Distracting, not delightful.
Performance tanks.
Content becomes secondary.
User fatigue.

**Instead**: Less is more.
Animate key moments.
Static content is okay.
Guide attention, don't overwhelm.

### ❌ Desktop-Only Experience

**Why bad**: Mobile is majority of traffic.
Touch scroll is different.
Performance issues on phones.
Unusable experience.

**Instead**: Mobile-first scroll design.
Simpler effects on mobile.
Test on real devices.
Graceful degradation.

## ⚠️ Sharp Edges

| Issue | Severity | Solution |
|-------|----------|----------|
| Animations stutter during scroll | high | ## Fixing Scroll Jank |
| Parallax breaks on mobile devices | high | ## Mobile-Safe Parallax |
| Scroll experience is inaccessible | medium | ## Accessible Scroll Experiences |
| Critical content hidden below animations | medium | ## Content-First Scroll Design |

## Related Skills

Works well with: `3d-web-experience`, `frontend`, `ui-design`, `landing-page-design`