NebulaBrowser/README-STEAM.md

Converting extracted AppImage (squashfs-root) into a distributable AppDir for Steam

If your environment lacks rsync, use cp -a to copy the extracted AppImage into a clean AppDir and prepare it for upload to Steam.

1. Copy the extracted AppImage to an AppDir folder

cp -a squashfs-root/ nebula-appdir

2. Unpack app.asar to edit or include app sources (optional; requires npx asar)

cd nebula-appdir/resources
npx asar extract app.asar app
# keep a backup if you want
mv app app.orig && rm app.asar
cd ../../

3. Add/verify launcher (we added nebula-appdir/Nebula):

chmod +x nebula-appdir/Nebula

Run locally:

cd nebula-appdir
./Nebula

4. Ensure binary & permissions are correct

chmod +x nebula-appdir/nebula

5. Package or upload to Steam

• Create a tarball to upload as game files, or upload the AppDir contents as the depot.

tar -czf nebula-appdir.tar.gz -C nebula-appdir .

• In Steamworks, set the launch command to ./Nebula (or ./nebula).

Notes

• --no-sandbox reduces Chromium sandboxing; prefer fixing chrome-sandbox and enabling sandboxing when possible.
• Using the AppDir avoids AppImage/FUSE dependency on target systems.
• Test on a clean SteamOS/Deck image before publishing.

Big Picture auto-start (SteamOS Gaming Mode)

• If Nebula is launched from SteamOS Gaming Mode, it will auto-start in Big Picture Mode.
• To force/disable via Steam Launch Options: --big-picture or --no-big-picture.

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Built-in Controller Support (Steam Deck / Game Mode)

Nebula has native gamepad support that signals to Steam that the application is consuming controller input. This prevents Steam from applying Desktop mouse/keyboard emulation when running in Game Mode.

How It Works

Steam Deck only stops applying Desktop mouse emulation when:

1. The application actively reads controller/gamepad input, OR
2. Steam Input is enabled (which requires explicit configuration)

If an app does not read controller input at all, Steam assumes the user needs mouse emulation.

Nebula solves this by:

1. Preload Gamepad Handler: The preload script (preload.js) continuously polls navigator.getGamepads() from the moment any window loads. This signals to Steam that the app is consuming gamepad events and should not apply mouse emulation.
2. Big Picture Mode: Full controller-friendly UI with:
   • D-pad / Left stick: Navigate menus
   • A button: Select/activate
   • B button: Back
   • X button: Backspace (in keyboard)
   • Y button: Space / Open search
   • LB/RB: Navigate webview history
   • Right stick: Virtual cursor (in browse mode)
   • Triggers: Left/right click (in browse mode)
   • Start: Toggle settings/sidebar
   • Select: Toggle fullscreen webview

Gamepad API (for Developers)

The gamepad handler exposes an API via window.gamepadAPI:

// Check if gamepad handler is initialized
if (gamepadAPI.isAvailable()) {
  console.log('Gamepad handler is running');
}

// Check if a gamepad is connected
if (gamepadAPI.isConnected()) {
  console.log('Gamepad connected!');
}

// Get list of connected gamepads
const gamepads = gamepadAPI.getConnected();
// Returns: [{ id, index, mapping, buttons, axes }, ...]
console.log(gamepads);

// Get active gamepad's current state (buttons and axes)
const active = gamepadAPI.getActive();
if (active) {
  console.log('Active gamepad:', active.id);
  console.log('Buttons:', active.buttons);
  console.log('Axes:', active.axes);
}

// Get handler state for debugging
const state = gamepadAPI.getState();
console.log('Handler state:', state);
// Returns: { initialized, connectedCount, activeGamepadIndex, isPolling }

// Listen for gamepad events (via CustomEvent on window)
window.addEventListener('nebula-gamepad-button', (e) => {
  const { button, pressed, value } = e.detail;
  console.log(`Button ${button}: ${pressed ? 'pressed' : 'released'}`);
});

window.addEventListener('nebula-gamepad-connect', (e) => {
  console.log('Gamepad connected:', e.detail.id);
});

window.addEventListener('nebula-gamepad-disconnect', (e) => {
  console.log('Gamepad disconnected:', e.detail.id);
});

window.addEventListener('nebula-gamepad-axis', (e) => {
  const { axis, value } = e.detail;
  console.log(`Axis ${axis}: ${value}`);
});

// Enable debug logging
gamepadAPI.setDebug(true);

Troubleshooting

If Steam is still applying mouse emulation:

1. Configure Steam Input per-game (most reliable fix):

   • In Steam, right-click Nebula → Properties → Controller
   • Set "Override for Nebula" to "Disable Steam Input"
   • This completely disables Steam's input emulation for this app

2. Verify gamepad polling is active: Open DevTools (F12) and run gamepadAPI.getState() - check that isPolling is true

3. Check gamepad connection: Run gamepadAPI.getConnected() to see detected gamepads

4. Press a button first: On Linux, the gamepadconnected event may not fire until the first button press

5. Enable debug mode: Run gamepadAPI.setDebug(true) to see detailed logs

6. Restart the app: Close Nebula completely and relaunch from Steam

Steam Launch Options

Add these to your Steam launch options (Right-click game → Properties → Launch Options):

# Disable Steam Input completely (recommended for native controller support)
SDL_GAMECONTROLLER_ALLOW_STEAM_VIRTUAL_GAMEPAD=0 %command%

# Force native gamepad without Steam's emulation layer
STEAM_INPUT_ENABLE_VIRTUAL_GAMEPAD=0 %command%

# Combined - full native controller mode with Big Picture UI
SDL_GAMECONTROLLER_ALLOW_STEAM_VIRTUAL_GAMEPAD=0 STEAM_INPUT_ENABLE_VIRTUAL_GAMEPAD=0 %command% --big-picture

# If you need to debug controller issues
SDL_GAMECONTROLLER_ALLOW_STEAM_VIRTUAL_GAMEPAD=0 %command% --big-picture 2>&1 | tee ~/nebula-debug.log

Steam Deck Recommended Setup

For the best experience on Steam Deck:

1. Add Nebula as a Non-Steam Game (if not using Steamworks version)
2. Controller Settings:
   • Right-click Nebula → Properties → Controller
   • Set to "Disable Steam Input"
3. Launch Options:

   SDL_GAMECONTROLLER_ALLOW_STEAM_VIRTUAL_GAMEPAD=0 STEAM_INPUT_ENABLE_VIRTUAL_GAMEPAD=0 %command% --big-picture
   

4. Shortcuts (optional):
   • Configure gamepad shortcuts in Steam for Steam button actions (screenshots, etc.)

Why This Is Needed

Steam Deck / SteamOS Game Mode applies "Desktop Configuration" mouse/keyboard emulation to apps that don't appear to handle controller input. Even though Nebula polls navigator.getGamepads() continuously, Steam's input layer initializes before the app can signal its intent.

The solution is two-fold:

1. Environment variables (SDL_GAMECONTROLLER_*) signal to Steam's SDL-based input layer early
2. Steam Input settings ("Disable Steam Input") bypasses the emulation entirely

Force Big Picture Mode

# Via command line
./Nebula --big-picture

# Via environment
NEBULA_BIG_PICTURE=1 ./Nebula

# Disable Big Picture Mode  
./Nebula --no-big-picture
NEBULA_NO_BIG_PICTURE=1 ./Nebula