Add glfwGetKeyName

Fixes #464.

src/x11_window.c

@@ -1939,6 +1939,34 @@ void _glfwPlatformSetCursorMode(_GLFWwindow* window, int mode)
     }
 }
 
+const char* _glfwPlatformGetKeyName(int key, int scancode)
+{
+    KeySym keysym;
+    int extra;
+
+    if (!_glfw.x11.xkb.available)
+        return NULL;
+
+    if (key != GLFW_KEY_UNKNOWN)
+        scancode = _glfw.x11.nativeKeys[key];
+
+    if (!_glfwIsPrintable(_glfw.x11.publicKeys[scancode]))
+        return NULL;
+
+    keysym = XkbKeycodeToKeysym(_glfw.x11.display, scancode, 0, 0);
+    if (keysym == NoSymbol)
+      return NULL;
+
+    XkbTranslateKeySym(_glfw.x11.display, &keysym, 0,
+                       _glfw.x11.keyName, sizeof(_glfw.x11.keyName),
+                       &extra);
+
+    if (!strlen(_glfw.x11.keyName))
+        return NULL;
+
+    return _glfw.x11.keyName;
+}
+
 int _glfwPlatformCreateCursor(_GLFWcursor* cursor,
                               const GLFWimage* image,
                               int xhot, int yhot)