[client] input: add support for evdev keyboard capture mode

The new configuration option `input:evdev` accepts a comma separated
list of `/dev/input/` keyboard devices to use for input when in capture
mode. This makes it possible to capture only a specific keyboard instead
of all keyboards.

client/include/app.h

@@ -59,8 +59,8 @@ void app_handleButtonPress(int button);
 void app_handleButtonRelease(int button);
 void app_handleWheelMotion(double motion);
 void app_handleKeyboardTyped(const char * typed);
-void app_handleKeyPress(int scancode, int charcode);
-void app_handleKeyRelease(int scancode, int charcode);
+void app_handleKeyPress(int scancode);
+void app_handleKeyRelease(int scancode);
 void app_handleKeyboardModifiers(bool ctrl, bool shift, bool alt, bool super);
 void app_handleKeyboardLEDs(bool numLock, bool capsLock, bool scrollLock);
 void app_handleEnterEvent(bool entered);

client/include/evdev.h

@@ -0,0 +1,46 @@
+/**
+ * Looking Glass
+ * Copyright © 2017-2025 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include <stdbool.h>
+
+/**
+ * initialize configuration options
+ */
+void evdev_earlyInit(void);
+
+/**
+ * start the evdev layer
+ */
+bool evdev_start(void);
+
+/**
+ * stop the evdev layer
+ */
+void evdev_stop(void);
+
+/**
+ * grab the keyboard for exclusive access
+ */
+void evdev_grabKeyboard(void);
+
+/**
+ * ungrab the keyboard
+ */
+void evdev_ungrabKeyboard(void);

client/include/interface/displayserver.h

@@ -183,6 +183,9 @@ struct LG_DisplayServerOps
   void (*capturePointer)(void);
   void (*uncapturePointer)(void);
 
+  /* get the character code for the provided scancode */
+  int (*getCharCode)(int sc);
+
   /* exiting = true if the warp is to leave the window */
   void (*warpPointer)(int x, int y, bool exiting);
 
@@ -253,6 +256,7 @@ struct LG_DisplayServerOps
   DEBUG_ASSERT((x)->ungrabPointer      ); \
   DEBUG_ASSERT((x)->capturePointer     ); \
   DEBUG_ASSERT((x)->uncapturePointer   ); \
+  DEBUG_ASSERT((x)->getCharCode        ); \
   DEBUG_ASSERT((x)->warpPointer        ); \
   DEBUG_ASSERT((x)->realignPointer     ); \
   DEBUG_ASSERT((x)->isValidPointerPos  ); \