Fix incorrect behavior of modifier keys on the right side of the keyboard

src/InputStream.c

@@ -561,14 +561,46 @@ int LiSendKeyboardEvent(short keyCode, char keyAction, char modifiers) {
         return -1;
     }
 
-    // Any keyboard event with the META modifier flag is dropped by all known GFE versions.
+    // For proper behavior, the MODIFIER flag must not be set on the modifier key down event itself
-    // This prevents us from sending shortcuts involving the meta key (Win+X, Win+Tab, etc).
+    // for the extended modifiers on the right side of the keyboard. If the MODIFIER flag is set,
-    // The catch is that the meta key event itself would actually work if it didn't set its
+    // GFE will synthesize an errant key down event for the non-extended key, causing that key to be
-    // own modifier flag, so we'll clear that here. This should be safe even if a new GFE
+    // stuck down after the extended modifier key is raised. For non-extended keys, we must set the
-    // release comes out that stops dropping events with MODIFIER_META flag.
+    // MODIFIER flag for correct behavior.
-    if ((keyCode & 0x00FF) == 0x5B || // VK_LWIN
+    switch (keyCode & 0xFF) {
-        (keyCode & 0x00FF) == 0x5C) { // VK_RWIN
+    case 0x5B: // VK_LWIN
+    case 0x5C: // VK_RWIN
+        // Any keyboard event with the META modifier flag is dropped by all known GFE versions.
+        // This prevents us from sending shortcuts involving the meta key (Win+X, Win+Tab, etc).
+        // The catch is that the meta key event itself would actually work if it didn't set its
+        // own modifier flag, so we'll clear that here. This should be safe even if a new GFE
+        // release comes out that stops dropping events with MODIFIER_META flag.
         modifiers &= ~MODIFIER_META;
+        break;
+
+    case 0xA0: // VK_LSHIFT
+        modifiers |= MODIFIER_SHIFT;
+        break;
+    case 0xA1: // VK_RSHIFT
+        modifiers &= ~MODIFIER_SHIFT;
+        break;
+
+    case 0xA2: // VK_LCONTROL
+        modifiers |= MODIFIER_CTRL;
+        break;
+    case 0xA3: // VK_RCONTROL
+        modifiers &= ~MODIFIER_CTRL;
+        break;
+
+    case 0xA4: // VK_LMENU
+        modifiers |= MODIFIER_ALT;
+        break;
+    case 0xA5: // VK_RMENU
+        modifiers &= ~MODIFIER_ALT;
+        break;
+
+    default:
+        // No fixups
+        break;
     }
 
     holder->packetLength = sizeof(NV_KEYBOARD_PACKET);