xkb is a compile-time option: a run-time option would also be possible, but the fallback XKeycodeToKeysym is deprecated on many platforms, and is preferably disabled if not necessary

CMakeLists.txt

@@ -238,12 +238,16 @@ if (_GLFW_X11)
         list(APPEND glfw_LIBRARIES Xxf86vm)
     endif()
 
+    option(GLFW_USE_XKB "Use the X keyboard extension" ON)
+    if(GLFW_USE_XKB)
         # Check for Xkb (X keyboard extension)
         if (NOT X11_Xkb_FOUND)
-        message(FATAL_ERROR "The X keyboard extension headers were not found")
-    endif() 
-
+            message("The X keyboard extension headers were not found")
+        else()
             list(APPEND glfw_INCLUDE_DIR ${X11_Xkb_INCLUDE_PATH})
+            set(_GLFW_USE_XKB 1)
+        endif()
+    endif()
 
     find_library(RT_LIBRARY rt)
     mark_as_advanced(RT_LIBRARY)

src/glfw_config.h.in

@@ -68,6 +68,8 @@
 #cmakedefine _GLFW_HAS_GLXGETPROCADDRESSEXT
 // Define this to 1 if dlopen is available
 #cmakedefine _GLFW_HAS_DLOPEN
+// Define this to 1 if Xkb is available
+#cmakedefine _GLFW_USE_XKB
 
 // Define this to 1 if glfwInit should change the current directory
 #cmakedefine _GLFW_USE_CHDIR

src/x11_init.c

@@ -44,6 +44,7 @@ static int translateKey(int keyCode)
     if (keyCode < 8 || keyCode > 255)
         return GLFW_KEY_UNKNOWN;
 
+#if defined(_GLFW_USE_XKB)
     // Try secondary keysym, for numeric keypad keys
     // Note: This way we always force "NumLock = ON", which is intentional
     // since the returned key code should correspond to a physical
@@ -72,6 +73,10 @@ static int translateKey(int keyCode)
     // should not be layout dependent (i.e. US layout and international
     // layouts should give the same result).
     keySym = XkbKeycodeToKeysym(_glfw.x11.display, keyCode, 0, 0);
+#else
+    keySym = XKeycodeToKeysym(_glfw.x11.display, keyCode, 0);
+#endif
+
     switch (keySym)
     {
         case XK_Escape:         return GLFW_KEY_ESCAPE;
@@ -216,7 +221,9 @@ static int translateKey(int keyCode)
 //
 static void updateKeyCodeLUT(void)
 {
-    int i, keyCode, keyCodeGLFW;
+    int keyCode, keyCodeGLFW;
+#if defined(_GLFW_USE_XKB)
+    int i;
     char name[XkbKeyNameLength + 1];
     XkbDescPtr descr;
 
@@ -302,6 +309,7 @@ static void updateKeyCodeLUT(void)
 
     // Free the keyboard description
     XkbFreeKeyboard(descr, 0, True);
+#endif
 
     // Translate the un-translated key codes using traditional X11 KeySym
     // lookups
@@ -481,6 +489,7 @@ static GLboolean initExtensions(void)
     }
 
     // Check if Xkb is supported on this display
+#if defined(_GLFW_USE_XKB)
     _glfw.x11.xkb.versionMajor = 1;
     _glfw.x11.xkb.versionMinor = 0;
     if (!XkbQueryExtension(_glfw.x11.display,
@@ -508,6 +517,7 @@ static GLboolean initExtensions(void)
                         "X11: Detectable key repeat is not supported");
         return GL_FALSE;
     }
+#endif
 
     // Update the key code LUT
     // FIXME: We should listen to XkbMapNotify events to track changes to

src/x11_platform.h

@@ -45,7 +45,9 @@
 #include <X11/extensions/XInput2.h>
 
 // The Xkb extension provides improved keyboard support
-#include <X11/XKBlib.h>
+#if defined(_GLFW_USE_XKB)
+ #include <X11/XKBlib.h>
+#endif
 
 #if defined(_GLFW_GLX)
  #define _GLFW_X11_CONTEXT_VISUAL window->glx.visual