# GSAP Scroll Animations Guide

GSAP scroll-driven animations for photographs and content. Animations are controlled by scroll position—scrolling down plays forward, scrolling up plays backward.

## Quick Start

```markdown
{% gsapScrollAnim {
  "animationType": "fadeIn",
  "scrollStart": "top 80%"
} %}
[{
  "src": "/path/to/image.jpg",
  "alt": "Image description",
  "caption": "Optional caption"
}]
{% endgsapScrollAnim %}
```

## Configuration Options

All parameters are optional with sensible defaults:

```javascript
{
  "animationType": "fadeIn",      // Animation preset (see below)
  "scrollStart": "top 80%",       // When animation starts
  "scrollEnd": "bottom 20%",      // When animation completes
  "scrub": true,                  // Tied to scroll position (bidirectional)
  "containerClass": "gsap-container", // CSS class for wrapper
  "pin": false,                   // Pin element during animation
  "markers": false                // Show debug markers (dev only)
}
```

### Animation Presets

- **fadeIn** - Fade in from below (opacity + translate Y)
- **fadeInUp** - Fade in from further below
- **fadeInDown** - Fade in from above
- **scaleIn** - Scale up with fade in (with bounce effect)
- **slideInLeft** - Slide in from left side
- **slideInRight** - Slide in from right side
- **parallax** - Subtle vertical parallax effect
- **stagger** - Sequential animation for multiple items

## Image Format

Images are defined as JSON array inside the paired shortcode:

```json
[{
  "src": "/path/to/image.jpg",
  "alt": "Required alt text",
  "caption": "Optional caption text"
}, {
  "src": "/path/to/image2.jpg",
  "alt": "Second image",
  "caption": "Another caption"
}]
```

Images are automatically optimized via Eleventy Image plugin (WebP/JPEG, responsive sizes).

## Examples

### Single Image with Fade In

```markdown
{% gsapScrollAnim {
  "animationType": "fadeIn"
} %}
[{
  "src": "/images/photo.jpg",
  "alt": "Description"
}]
{% endgsapScrollAnim %}
```

### Multiple Images with Stagger

```markdown
{% gsapScrollAnim {
  "animationType": "stagger",
  "scrollStart": "top 70%"
} %}
[{
  "src": "/images/photo1.jpg",
  "alt": "First photo",
  "caption": "Photo 1"
}, {
  "src": "/images/photo2.jpg",
  "alt": "Second photo",
  "caption": "Photo 2"
}]
{% endgsapScrollAnim %}
```

### Parallax Effect

```markdown
{% gsapScrollAnim {
  "animationType": "parallax",
  "scrub": true
} %}
[{
  "src": "/images/background.jpg",
  "alt": "Background scene"
}]
{% endgsapScrollAnim %}
```

### Custom Container Class

```markdown
{% gsapScrollAnim {
  "animationType": "scaleIn",
  "containerClass": "gsap-container featured-image"
} %}
[{
  "src": "/images/hero.jpg",
  "alt": "Hero image"
}]
{% endgsapScrollAnim %}
```

## ScrollTrigger Settings

### scrollStart / scrollEnd

Control when the animation begins and ends relative to viewport:

- `"top bottom"` - Element's top enters viewport bottom
- `"top 80%"` - Element's top at 80% viewport height
- `"center center"` - Element center aligns with viewport center
- `"bottom top"` - Element bottom exits viewport top

Default: `scrollStart: "top 80%"`, `scrollEnd: "bottom 20%"`

### scrub

When `true` (default), animation progress is tied directly to scroll position, enabling bidirectional playback.

When `false`, animation plays once when scroll position crosses `scrollStart` threshold.

## CSS Customization

Default wrapper class: `.gsap-container`

Generated structure:
```html
<div class="gsap-container" data-gsap-scroll-anim='{...}'>
  <div class="gsap-item">
    <figure class="gsap-image-wrapper">
      <picture>
        <img class="gsap-image" src="..." alt="...">
      </picture>
      <figcaption>...</figcaption>
    </figure>
  </div>
</div>
```

Add custom styles in your CSS:
```css
.gsap-container.featured-image {
  max-width: 1200px;
  margin: 0 auto;
}

.gsap-item {
  margin-bottom: 2rem;
}
```

## Accessibility

- Respects `prefers-reduced-motion` - animations disabled automatically
- All images require `alt` text
- ScrollTrigger callbacks maintain proper ARIA states

## Turbo Drive Compatibility

Animations are automatically cleaned up and re-initialized on Turbo navigation:
- Contexts reverted before page change
- ScrollTrigger instances killed
- Re-initialized after new page loads

## Debugging

Enable debug markers to visualize scroll trigger points:

```markdown
{% gsapScrollAnim {
  "animationType": "fadeIn",
  "markers": true
} %}
[...]
{% endgsapScrollAnim %}
```

This shows colored markers in viewport indicating trigger start/end positions.

## Performance

- Animations use GPU-accelerated properties (`transform`, `opacity`)
- `will-change` applied for optimization
- ScrollTrigger efficiently batches calculations
- Contexts properly cleaned up on navigation

## Files Modified

- **Shortcode**: `src/_config/shortcodes/gsap.js`
- **Initializer**: `src/assets/scripts/bundle/gsap-shortcode-init.js`
- **CSS**: `src/assets/css/global/utilities/gsap-animations.css`
- **Config**: Registered in `eleventy.config.js` as paired shortcode