# Contours

A topographic map: contour lines over slowly drifting hills.

## Installation

```sh
pnpm add astro-dither
```

Or copy the source into your project:

```sh
npx astro-dither add effect
```

## Usage

```astro
---
import { DitherEffect } from "astro-dither";
---

<DitherEffect effect="contours" />
```

Fractal height sliced into contour bands, with the hillshade kept under the lines. `scale` zooms the terrain and `lines` sets how many elevation bands the map draws.

The props group like this:

Terrain: `scale`, `lines`.

## Examples

### Flat land

Few `lines` read like a calm, low-relief map.

```astro
<DitherEffect effect="contours" params={{"lines":4}} />
```

### Alps

More `lines` at a bigger `scale` give dense alpine ridges.

```astro
<DitherEffect effect="contours" params={{"scale":3.5,"lines":24}} />
```

## Props

| Prop | Type | Default | Description |
| --- | --- | --- | --- |
| `scale` | `number` | 2 | Terrain zoom. 0.5 to 6. |
| `lines` | `number` | 10 | Contour bands drawn. 2 to 30. |
| `palette` | `string[]` | the effect's | 2 to 8 colours, paper first, brightest last. `transparent` works. |
| `cell` | `number` | 2 | Size of one dither cell in CSS pixels. Rounded to whole device pixels so cells stay even. |
| `matrix` | `2 | 4 | 8 | "noise"` | 8 | The Bayer threshold size, or noise for a random look. |
| `speed` | `number` | 1 | Playback speed. 0 draws one still frame. |
| `stillTime` | `number` | the effect's | The moment drawn when motion is off or reduced, in seconds. |
| `levels` | `number` | 0 (all) | Tones the field snaps to before dithering. Low values give hard, posterised steps. |
| `bloom` | `number` | 0 | Bloom around lit cells, 0 to 1. Set a positive prop to create the overlay before overriding it with CSS `--dither-bloom`. |
| `bloomRadius` | `number` | 10 | Bloom blur in CSS pixels. CSS `--dither-bloom-radius` overrides it. |
| `class` | `string` | undefined | Classes on the surface element, for size and position. |

## Notes

* Decorative and `aria-hidden`. Put real text on top, not inside it.
* With reduced motion it draws one still frame (at 5s) and stops.
* It pauses when scrolled out of view or when the tab is hidden.
* Shares one WebGL context with every other ordered effect on the page.