Canvas
Display HTML content on connected Bitterbot nodes (Mac app, iOS, Android).
Overview
The canvas tool lets you present web content on any connected node's canvas view. Great for:
- Displaying games, visualizations, dashboards
- Showing generated HTML content
- Interactive demos
How It Works
Architecture
┌─────────────────┐ ┌──────────────────┐ ┌─────────────┐ │ Canvas Host │────▶│ Node Bridge │────▶│ Node App │ │ (HTTP Server) │ │ (TCP Server) │ │ (Mac/iOS/ │ │ Port 18793 │ │ Port 18790 │ │ Android) │ └─────────────────┘ └──────────────────┘ └─────────────┘
- Canvas Host Server: Serves static HTML/CSS/JS files from
canvasHost.rootdirectory - Node Bridge: Communicates canvas URLs to connected nodes
- Node Apps: Render the content in a WebView
Tailscale Integration
The canvas host server binds based on gateway.bind setting:
| Bind Mode | Server Binds To | Canvas URL Uses |
|---|---|---|
loopback | 127.0.0.1 | localhost (local only) |
lan | LAN interface | LAN IP address |
tailnet | Tailscale interface | Tailscale hostname |
auto | Best available | Tailscale > LAN > loopback |
Key insight: The canvasHostHostForBridge is derived from bridgeHost. When bound to Tailscale, nodes receive URLs like:
http://<tailscale-hostname>:18793/__bitterbot__/canvas/<file>.html
This is why localhost URLs don't work - the node receives the Tailscale hostname from the bridge!
Actions
| Action | Description |
|---|---|
present | Show canvas with optional target URL |
hide | Hide the canvas |
navigate | Navigate to a new URL |
eval | Execute JavaScript in the canvas |
snapshot | Capture screenshot of canvas |
Configuration
In ~/.bitterbot/bitterbot.json:
json{ "canvasHost": { "enabled": true, "port": 18793, "root": "/Users/you/bitterbot/canvas", "liveReload": true }, "gateway": { "bind": "auto" } }
Live Reload
When liveReload: true (default), the canvas host:
- Watches the root directory for changes (via chokidar)
- Injects a WebSocket client into HTML files
- Automatically reloads connected canvases when files change
Great for development!
Workflow
1. Create HTML content
Place files in the canvas root directory (default ~/bitterbot/canvas/):
bashcat > ~/bitterbot/canvas/my-game.html << 'HTML' <!DOCTYPE html> <html> <head><title>My Game</title></head> <body> <h1>Hello Canvas!</h1> </body> </html> HTML
2. Find your canvas host URL
Check how your gateway is bound:
bashcat ~/.bitterbot/bitterbot.json | jq '.gateway.bind'
Then construct the URL:
- loopback:
http://127.0.0.1:18793/__bitterbot__/canvas/<file>.html - lan/tailnet/auto:
http://<hostname>:18793/__bitterbot__/canvas/<file>.html
Find your Tailscale hostname:
bashtailscale status --json | jq -r '.Self.DNSName' | sed 's/\.$//'
3. Find connected nodes
bashbitterbot nodes list
Look for Mac/iOS/Android nodes with canvas capability.
4. Present content
canvas action:present node:<node-id> target:<full-url>
Example:
canvas action:present node:mac-63599bc4-b54d-4392-9048-b97abd58343a target:http://peters-mac-studio-1.sheep-coho.ts.net:18793/__bitterbot__/canvas/snake.html
5. Navigate, snapshot, or hide
canvas action:navigate node:<node-id> url:<new-url> canvas action:snapshot node:<node-id> canvas action:hide node:<node-id>
Debugging
White screen / content not loading
Cause: URL mismatch between server bind and node expectation.
Debug steps:
- Check server bind:
cat ~/.bitterbot/bitterbot.json | jq '.gateway.bind' - Check what port canvas is on:
lsof -i :18793 - Test URL directly:
curl http://<hostname>:18793/__bitterbot__/canvas/<file>.html
Solution: Use the full hostname matching your bind mode, not localhost.
"node required" error
Always specify node:<node-id> parameter.
"node not connected" error
Node is offline. Use bitterbot nodes list to find online nodes.
Content not updating
If live reload isn't working:
- Check
liveReload: truein config - Ensure file is in the canvas root directory
- Check for watcher errors in logs
URL Path Structure
The canvas host serves from /__bitterbot__/canvas/ prefix:
http://<host>:18793/__bitterbot__/canvas/index.html → ~/bitterbot/canvas/index.html http://<host>:18793/__bitterbot__/canvas/games/snake.html → ~/bitterbot/canvas/games/snake.html
The /__bitterbot__/canvas/ prefix is defined by CANVAS_HOST_PATH constant.
Tips
- Keep HTML self-contained (inline CSS/JS) for best results
- Use the default index.html as a test page (has bridge diagnostics)
- The canvas persists until you
hideit or navigate away - Live reload makes development fast - just save and it updates!
- A2UI JSON push is WIP - use HTML files for now
