Add grave modifier support for hotkeys

Implements support for using the grave key (`) as a hotkey modifier
in Barrier, enabling hotkey combinations like Grave+1, Grave+2, etc.

Key changes:
- Add XK_grave case to getModifierBitForKeySym() for XKB support
- Add fallback mapping for grave modifier to Mod4 in XKB path
- Include KeyModifierGrave in allowed modifiers for hotkey registration
- Add setup documentation for required X11 modifier mapping

Requires running: xmodmap -e "add mod4 = grave"

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

GRAVE_MODIFIER_SETUP.md

@@ -0,0 +1,48 @@
+# Grave Modifier Setup for Barrier
+
+## Overview
+This implementation adds support for using the grave key (`) as a hotkey modifier in Barrier, similar to Control, Alt, and Shift.
+
+## Required Setup
+
+### 1. Code Changes
+The following code changes have been implemented:
+
+- **XWindowsUtil.cpp**: Added `case XK_grave: return kKeyModifierBitGrave;` to `getModifierBitForKeySym()`
+- **XWindowsKeyState.cpp**: Added fallback mapping for grave modifier to Mod4 in `updateKeysymMapXKB()`
+- **key_types.cpp**: Already included grave modifier in `kModifierNameMap`
+
+### 2. X11 Modifier Mapping (REQUIRED)
+The grave key must be mapped to an X11 modifier for hotkeys to work. Run this command:
+
+```bash
+xmodmap -e "add mod4 = grave"
+```
+
+### 3. Make it Permanent
+To make the X11 mapping persistent across reboots, add this line to `~/.xsessionrc`:
+
+```bash
+echo 'xmodmap -e "add mod4 = grave"' >> ~/.xsessionrc
+```
+
+## Usage
+Once setup is complete, you can use grave modifier hotkeys in your Barrier configuration:
+
+```
+keystroke(Grave+1) = switchToScreen(screen1,960,540)
+keystroke(Grave+2) = switchToScreen(screen2,960,540)
+```
+
+## Verification
+To verify the setup:
+
+1. Check modifier mapping: `xmodmap -pm`
+   - Should show `grave (0x31)` in the mod4 line
+2. Test hotkeys: Press and hold grave, then press a number key
+3. Check Barrier logs for successful hotkey registration
+
+## Troubleshooting
+- If hotkeys don't work, verify grave is mapped to mod4: `xmodmap -pm`
+- If mapping is lost after reboot, ensure `~/.xsessionrc` contains the xmodmap command
+- Restart Barrier server after making X11 mapping changes

src/lib/platform/XWindowsKeyState.cpp

@@ -317,6 +317,7 @@ XWindowsKeyState::updateKeysymMap(barrier::KeyMap& keyMap)
     m_modifierToX[KeyModifierShift]    = ShiftMask;
     m_modifierToX[KeyModifierCapsLock] = LockMask;
     m_modifierToX[KeyModifierControl]  = ControlMask;
+    m_modifierToX[KeyModifierGrave]    = Mod4Mask;
 
     // prepare map from KeyID to KeyCode
     m_keyCodeFromKey.clear();
@@ -779,6 +780,16 @@ XWindowsKeyState::updateKeysymMapXKB(barrier::KeyMap& keyMap)
         }
     }
 
+    // Add fallback for grave modifier if not found during XKB discovery
+    if (m_modifierToX.find(KeyModifierGrave) == m_modifierToX.end()) {
+        LOG((CLOG_DEBUG1 "XKB: Adding fallback mapping for grave modifier to Mod4"));
+        m_modifierToX[KeyModifierGrave] = Mod4Mask;
+        // Also update the reverse mapping for consistency
+        if (m_modifierFromX.size() > 3) {  // Mod4 is bit 3
+            m_modifierFromX[3] |= KeyModifierGrave;
+        }
+    }
+
     // change all modifier masks to barrier masks from X masks
     keyMap.foreachKey(&XWindowsKeyState::remapKeyModifiers, this);
 

src/lib/platform/XWindowsScreen.cpp

@@ -528,7 +528,7 @@ XWindowsScreen::registerHotKey(KeyID key, KeyModifierMask mask)
 {
 	// only allow certain modifiers
 	if ((mask & ~(KeyModifierShift | KeyModifierControl |
-				  KeyModifierAlt   | KeyModifierSuper)) != 0) {
+				  KeyModifierAlt   | KeyModifierSuper | KeyModifierGrave)) != 0) {
 		LOG((CLOG_DEBUG "could not map hotkey id=%04x mask=%04x", key, mask));
 		return 0;
 	}

src/lib/platform/XWindowsUtil.cpp

@@ -1646,6 +1646,9 @@ XWindowsUtil::getModifierBitForKeySym(KeySym keysym)
     case XK_Scroll_Lock:
         return kKeyModifierBitScrollLock;
 
+    case XK_grave:
+        return kKeyModifierBitGrave;
+
     default:
         return kKeyModifierBitNone;
     }