# GSAP Animation System (Punch animations)

This project uses GSAP for scroll-driven punch animations (zoom in/out effects) via shortcodes. The system is intentionally minimal and focused on high-quality image reveals.

## Architecture Overview

The animation system is split into two main parts:

1. **Animations Library** ([`gsap-animations.js`](../src/assets/scripts/bundle/gsap-animations.js))
  - Reusable zoom presets: `punchIn`, `punchOut`
  - Default variables with simple override merging
  - `shouldAnimate()` utility respecting `prefers-reduced-motion`

2. **Content Animations** ([`gsap-shortcode-init.js`](../src/assets/scripts/bundle/gsap-shortcode-init.js))
  - Scroll-triggered animations in markdown/blog posts
  - Paired shortcode reads JSON config and passes it through. The shortcode also passes arguments for a Tailwind class name.
  - We must remember that this is the only function of Tailwind that we use and that we should consult files in ([`our design tokens`](../src/assets/css/global/global.css)), and be mindful of the fact that these animations will exist as containers of ([`prose.css`](../src/assets/css/global/blocks/prose.css)).

---

# For Content Authors

See [GSAP_USAGE.md](./GSAP_USAGE.md) for shortcode usage.

## Quick Start

### Punch In Animation

```markdown
{% gsapScrollAnim { "animationType": "punchIn", "focalX": 75, "focalY": 25, "startZoom": 1, "endZoom": 2.5 } %}
[{ "src": "/images/detail-photo.jpg", "alt": "Macro photography showing fine detail" }]
{% endgsapScrollAnim %}
```

---

# For Developers

## Configuration Options

All parameters are optional with sensible defaults and fully passed through:

```javascript
{
  "animationType": "punchIn",      // punchIn or punchOut
  "scrollStart": "top 80%",       // Timeline start
  "scrollEnd": "bottom 20%",      // Timeline end
  "scrub": true,                   // Tie progress to scroll
  "containerClass": "gsap-container",
  "spillingInto": false,           // false | true | 'prose' | 'bleed'
  "pin": true,
  "markers": false,
  // Punch-specific overrides
  "focalX": 50,                    // 0-100 (% from left)
  "focalY": 50,                    // 0-100 (% from top)
  "startZoom": 1,                  // 1 for punchIn, 2.5 for punchOut
  "endZoom": 2.5,                  // 2.5 for punchIn, 1 for punchOut
  "ease": "power2.inOut"
}
```

## 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).

## Example

### Zoom In to Focal Point

Draw attention to a specific detail in a high-resolution photograph:

```markdown
{% gsapScrollAnim {
  "animationType": "zoomIn",
  "focalX": 75,
  "focalY": 25,
  "startZoom": 1,
  "endZoom": 2.5
} %}
[{
  "src": "/images/detail-photo.jpg",
  "alt": "Macro photography showing fine detail"
}]
{% endgsapScrollAnim %}
```

**Zoom Parameters:**
- `focalX` (0-100): Horizontal focal point percentage from left (default: 50)
- `focalY` (0-100): Vertical focal point percentage from top (default: 50)
- `startZoom`: Initial scale (default: 1 = 100%)
- `endZoom`: Final scale (default: 2.5 = 250%)

**zoomIn**: Starts with full image visible, zooms into the focal point
**zoomOut**: Starts zoomed into focal point, pulls back to show full image

High-resolution images (up to 3200px) are automatically loaded for zoom animations to preserve detail when scaled.

## 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

- Library: `src/assets/scripts/bundle/gsap-animations.js`
- Shortcode initializer: `src/assets/scripts/bundle/gsap-shortcode-init.js`
- Shortcode: `src/_config/shortcodes/gsap.js`
- CSS: `src/assets/css/global/utilities/gsap-animations.css`