@scratcher.js/svelte

Svelte 5 bindings for scratcher.js — a A lightweight library for building expressive Scratch interactions.

Documentation

Full docs, API reference, and examples - Scratcher.js | Docs

Install

npm i @scratcher.js/svelte

Requires svelte >= 5 as a peer dependency.

Quick start

<script lang="ts">
  import { Scratcher } from '@scratcher.js/svelte';

  const config = {
    width: 400,
    height: 240,
    brushSize: 30,
    cover: '#ccc',
    completionThreshold: 0.5,
    onProgress: (snap) => console.log('Progress:', snap.progress),
    onComplete: () => alert('Scratching complete!'),
  };
</script>

<Scratcher {...config}>
  <div class="reward">You found it!</div>
</Scratcher>

Configuration

All ScratcherConfig options from @scratcher.js/core are accepted as props.

| Prop | Type | Required | Description | Default | | --------------------- | ---------------------------- | :------: | --------------------------------------------------------- | ----------- | | width | number | ✓ | Canvas width (px). Drawing-buffer size; also the wrapper's display width (or max width when responsive). | — | | height | number | ✓ | Canvas height (px). Drawing-buffer size; ignored for display when responsive (computed from aspect-ratio). | — | | brushSize | number | ✓ | Brush diameter (px) | — | | cellSize | number | | Grid cell size (px) for progress tracking. Lower = finer. | 16 | | completionThreshold | number (0~1) | | Progress at which onComplete fires | 0.5 | | revealOnCompletion | boolean | | Auto-clear the cover when threshold is reached | false | | cover | string | | Cover color or image URL | '#b9c2ce' | | responsive | boolean | | Shrink to fit narrower parents while preserving aspect ratio — see Responsive sizing. | false | | area | RectArea \| ImageArea | | Restrict progress measurement to a region | — | | callbacks | ScratchControllerCallbacks | | Event handlers (see below) | — | | mapPoint | function | | Custom pointer → canvas coordinate mapper | built-in | | renderAtPoint | function | | Custom brush-stroke renderer | built-in | | renderCover | function | | Custom cover-layer renderer | built-in |

Callbacks

All callbacks receive ScratchSnapshot — { scratchedCells, totalCells, progress, area? }.

| Callback | Signature | Triggered | | ---------------- | --------------------------- | --------------------------- | | onScratchStart | (point, snapshot) => void | Pointer down on the canvas | | onScratchMove | (point, snapshot) => void | Pointer move while drawing | | onScratchEnd | (snapshot) => void | Pointer up / leave / cancel | | onReset | (snapshot) => void | reset() called | | onProgress | (snapshot) => void | Any progress change | | onComplete | (snapshot) => void | Threshold first reached |

Responsive sizing

By default the wrapper renders at a fixed width × height. Pass responsive to make it shrink to fit narrower parents while preserving its aspect ratio:

<Scratcher {...config} responsive>
  <div class="reward">You found it!</div>
</Scratcher>

When responsive is enabled, the wrapper renders with width: ${width}px; max-width: 100%; min-width: 0; aspect-ratio: ${width} / ${height}:

• Parent ≥ width: rendered at the exact width × height (same as the fixed-size default).
• Parent < width: shrinks proportionally to the parent's width.

Pointer coordinates are scaled internally by the core engine regardless of responsive, so scratches stay aligned with the cursor even when the canvas is CSS-scaled (whether via this prop or your own styles).

If you place custom overlays (e.g. area markers) inside a responsive wrapper, prefer percentage coordinates (left: 18.75%) over pixels so they scale with the canvas.

Svelte-specific props

| Prop | Type | Description | | ------------------ | ------------------------------------ | --------------------------------------------------- | | class | string | Class on the wrapper <div> | | canvasClass | string | Class on the inner <canvas> | | rewardClass | string | Class on the reward layer | | onScratcherReady | (scratcher: CoreScratcher) => void | Receive the underlying engine instance once mounted | | children | Snippet | Rendered as the reveal layer below the cover |

License

MIT