rplace

A collaborative pixel art canvas inspired by Reddit's r/place. Place pixels, create art together in real-time.

Features

• 4096×4096 canvas with a 256-color palette (16-step grayscale + 240-hue HSL wheel)
• Real-time updates via WebSocket (Cloudflare Durable Objects)
• Batch pixel placement up to 2048 pixels per request
• Rate limit — 1 request per second per user (batch size independent)
• Zoom/pan with mouse wheel + drag (desktop) and pinch-zoom + drag (mobile)
• Long-press to place on touch devices
• Image importer — upload, dither, and auto-paint images onto the canvas

Tech Stack

Layer	Technology
Frontend	Svelte 5 (runes) + HTML5 Canvas
Backend	Hono on Cloudflare Workers
Real-time	WebSocket via Cloudflare Durable Objects
Storage	Upstash Redis (BITFIELD for canvas, SET NX EX for rate limiting)
Build	Vite

Architecture

Browser (Svelte SPA + WebSocket)
  |  GET  /api/canvas  → full canvas binary (16MB raw, ~5MB gzip)
  |  POST /api/place   → batch pixel placement
  |  WS   /api/ws      → Durable Object broadcast room
  v
Cloudflare Worker (Hono)
  ├── Canvas API (read/write pixels via Redis BITFIELD)
  ├── Rate Limiter (SET NX EX — atomic per-user cooldown)
  └── Durable Object (WebSocket broadcast to all clients)
        ↕
Upstash Redis
  ├── STRING "canvas:v2" (1 byte per pixel, 4096×4096 = 16 MB)
  └── STRING "cooldown:{userId}" (1s TTL, blocks repeat requests)

Getting Started

Prerequisites

• Node.js 18+
• Cloudflare account (free tier works)
• Upstash Redis database (free tier works)

Setup

# Clone and install
git clone <repo-url>
cd rplace
npm install

# Configure environment
cp .env.example .env
# Edit .env with your Upstash Redis credentials

# For wrangler (Cloudflare Workers CLI)
npx wrangler secret put UPSTASH_REDIS_REST_URL
npx wrangler secret put UPSTASH_REDIS_REST_TOKEN

Development

# Run worker locally (serves both API and frontend)
npm run dev

# Or run frontend and worker separately
npm run dev:client   # Vite dev server on :5173 (proxies /api to :8787)
npm run dev          # Wrangler dev server on :8787

Deploy

npm run deploy   # Builds frontend + deploys worker to Cloudflare

Project Structure

src/
├── worker.js                          # Hono API entry point
├── durable-objects/
│   └── canvas-room.js                 # WebSocket broadcast room
├── lib/
│   ├── constants.js                   # Config, palette, limits (shared)
│   ├── redis-client.js                # Upstash Redis factory
│   ├── canvas-storage.js              # BITFIELD read/write
│   ├── canvas-decoder.js              # Raw bytes → RGBA (client-side; u8 = identity indices)
│   ├── rate-limiter.js                # SET NX EX cooldown
│   ├── image-uploader.js              # Browser-side batched uploader
│   └── get-user-id.js                 # IP-based identity
├── client/
│   ├── main.js                        # Svelte mount
│   ├── App.svelte                     # Root + WebSocket
│   ├── app.css                        # Global styles
│   └── components/
│       ├── CanvasRenderer.svelte      # Canvas + zoom/pan + touch
│       ├── ColorPicker.svelte         # Favorites strip + 256-color grid + custom picker
│       ├── CanvasControls.svelte      # Zoom buttons + coordinates
│       ├── DrawToolbar.svelte         # Paint / submit / undo / redo
│       └── ImageImporter.svelte       # Image-to-canvas uploader
└── index.html                         # Vite entry

API

GET /api/canvas

Returns the full canvas as raw binary (1 byte per pixel, 16 MB — Cloudflare gzips it on the edge).

POST /api/place

Place pixels on the canvas.

{
  "pixels": [
    { "x": 100, "y": 200, "color": 27 }
  ]
}

Response: { "ok": true }

Errors:

• 400 — invalid pixel data or batch > 2048
• 413 — request body too large
• 429 — rate limited (includes retryAfter seconds)

WS /api/ws

WebSocket for real-time pixel updates. Messages are JSON:

{ "type": "pixels", "pixels": [{ "x": 100, "y": 200, "color": 27 }] }

Configuration

Key constants in src/lib/constants.js:

Constant	Default	Description
CANVAS_WIDTH	4096	Canvas width in pixels
CANVAS_HEIGHT	4096	Canvas height in pixels
MAX_COLORS	256	Number of palette entries
BITS_PER_PIXEL	8	Byte-aligned (storage = W × H bytes)
MAX_BATCH_SIZE	2048	Max pixels per placement request
REQUEST_COOLDOWN_SEC	1	Minimum seconds between requests per user

Credits & References

• Reddit on Building & Scaling r/place (Fastly)
• Engineering Behind r/place (Sai Kumar Chintada)
• Redis Place: Building r/place with 9 Redis Data Structures (Mehdi Amrane)
• Redis Pixel War (Alfredo Salzillo)
• Redis BITFIELD Command
• reddit-plugin-place-opensource
• rPlace by anthonytedja
• redis-place by mehdiamrane
• redis-challenge by alfredosalzillo
• place by dynastic
• rplace.live — original 32-color palette reference (since superseded by our 256-color HSL wheel)

License

MIT