Automatically detect Xkb at run-time.

Uses XGetKeyboardMapping as a fallback.  Fixes #282.

README.md

@@ -78,6 +78,7 @@ The following dependencies are needed by the examples and test programs:
                    the error callback
  - [Win32] Bugfix: Some keys were reported based on the current layout instead
                    of their physical location
+ - [X11] Added run-time support for systems lacking the XKB extension
  - [X11] Made GLX 1.3 the minimum supported version
  - [X11] Bugfix: The case of finding no usable CRTCs was not detected
  - [X11] Bugfix: Detection of broken Nvidia RandR gamma support did not verify

src/x11_init.c

@@ -40,11 +40,15 @@
 static int translateKey(int keyCode)
 {
     int keySym;
+    int keysyms_per_keycode_return;
+    KeySym *keysyms;
 
     // Valid key code range is  [8,255], according to the XLib manual
     if (keyCode < 8 || keyCode > 255)
         return GLFW_KEY_UNKNOWN;
 
+    if(_glfw.x11.xkb.available)
+    {
         // 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
@@ -73,6 +77,18 @@ 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
+    {
+        keysyms =
+        XGetKeyboardMapping(_glfw.x11.display,
+                            keyCode,
+                            1,
+                            &keysyms_per_keycode_return);
+        keySym = keysyms[0];
+        XFree(keysyms);
+    }
+
     switch (keySym)
     {
         case XK_Escape:         return GLFW_KEY_ESCAPE;
@@ -217,7 +233,8 @@ static int translateKey(int keyCode)
 //
 static void updateKeyCodeLUT(void)
 {
-    int i, keyCode, keyCodeGLFW;
+    int keyCode;
+    int keyCodeGLFW, i;
     char name[XkbKeyNameLength + 1];
     XkbDescPtr descr;
 
@@ -225,6 +242,8 @@ static void updateKeyCodeLUT(void)
     for (keyCode = 0;  keyCode < 256;  keyCode++)
         _glfw.x11.keyCodeLUT[keyCode] = GLFW_KEY_UNKNOWN;
 
+    if(_glfw.x11.xkb.available)
+    {
         // Use XKB to determine physical key locations independently of the current
         // keyboard layout
 
@@ -303,6 +322,7 @@ static void updateKeyCodeLUT(void)
 
         // Free the keyboard description
         XkbFreeKeyboard(descr, 0, True);
+    }
 
     // Translate the un-translated key codes using traditional X11 KeySym
     // lookups
@@ -496,30 +516,27 @@ static GLboolean initExtensions(void)
     // Check if Xkb is supported on this display
     _glfw.x11.xkb.versionMajor = 1;
     _glfw.x11.xkb.versionMinor = 0;
-    if (!XkbQueryExtension(_glfw.x11.display,
+    _glfw.x11.xkb.available =
+        XkbQueryExtension(_glfw.x11.display,
                           &_glfw.x11.xkb.majorOpcode,
                           &_glfw.x11.xkb.eventBase,
                           &_glfw.x11.xkb.errorBase,
                           &_glfw.x11.xkb.versionMajor,
-                           &_glfw.x11.xkb.versionMinor))
+                          &_glfw.x11.xkb.versionMinor);
-    {
-        _glfwInputError(GLFW_PLATFORM_ERROR,
-                        "X11: The keyboard extension is not available");
-        return GL_FALSE;
-    }
 
+    if(_glfw.x11.xkb.available)
+    {
         if (!XkbSetDetectableAutoRepeat(_glfw.x11.display, True, &supported))
         {
-        _glfwInputError(GLFW_PLATFORM_ERROR,
+            // X11: Failed to set detectable key repeat
-                        "X11: Failed to set detectable key repeat");
+            _glfw.x11.xkb.available = GL_FALSE;
-        return GL_FALSE;
         }
 
         if (!supported)
         {
-        _glfwInputError(GLFW_PLATFORM_ERROR,
+            // X11: Detectable key repeat is not supported
-                        "X11: Detectable key repeat is not supported");
+            _glfw.x11.xkb.available = GL_FALSE;
-        return GL_FALSE;
+        }
     }
 
     // Update the key code LUT

src/x11_platform.h

@@ -175,6 +175,7 @@ typedef struct _GLFWlibraryX11
     } randr;
 
     struct {
+        GLboolean   available;
         int         majorOpcode;
         int         eventBase;
         int         errorBase;