X11: handle XI device hotplugging

Fixes #9370

glfw/x11_init.c

@@ -148,7 +148,7 @@ static void detectEWMH(void)
     XFree(supportedAtoms);
 }
 
-static void
+void
 read_xi_scroll_devices(void) {
 #define xi _glfw.x11.xi
     xi.num_scroll_devices = 0;
@@ -512,6 +512,19 @@ static bool initExtensions(void)
     _glfw.x11.xi.LIBINPUT_SCROLL_METHOD_ENABLED = XInternAtom(_glfw.x11.display, "libinput Scroll Method Enabled", False);
     read_xi_scroll_devices();
 
+    // Select XI_HierarchyChanged events to detect device add/remove
+    if (_glfw.x11.xi.available) {
+        XIEventMask em;
+        unsigned char mask[XIMaskLen(XI_HierarchyChanged)] = { 0 };
+
+        em.deviceid = XIAllDevices;
+        em.mask_len = sizeof(mask);
+        em.mask = mask;
+        XISetMask(mask, XI_HierarchyChanged);
+
+        XISelectEvents(_glfw.x11.display, _glfw.x11.root, &em, 1);
+    }
+
     // The compositing manager selection name contains the screen number
     {
         char name[32];

glfw/x11_platform.h

@@ -498,3 +498,5 @@ void _glfwInputErrorX11(int error, const char* message);
 
 void _glfwGetSystemContentScaleX11(float* xscale, float* yscale, bool bypass_cache);
 void _glfwPushSelectionToManagerX11(void);
+void read_xi_scroll_devices(void);
+

glfw/x11_window.c

@@ -58,7 +58,6 @@
 
 #define _GLFW_XDND_VERSION 5
 
-
 // Wait for data to arrive using poll
 // This avoids blocking other threads via the per-display Xlib lock that also
 // covers GLX functions
@@ -1388,6 +1387,20 @@ static void processEvent(XEvent *event)
                         }
                     }
                 }
+                // Handle XI_HierarchyChanged for device hotplug
+                else if (event->xcookie.evtype == XI_HierarchyChanged)
+                {
+                    XIHierarchyEvent* he = (XIHierarchyEvent*)event->xcookie.data;
+                    // Check if any devices were added or removed
+                    for (int i = 0; i < he->num_info; i++) {
+                        if (he->info[i].flags & (XISlaveAdded | XISlaveRemoved |
+                                                  XIMasterAdded | XIMasterRemoved)) {
+                            // Re-read scroll devices when devices are added or removed
+                            read_xi_scroll_devices();
+                            break;
+                        }
+                    }
+                }
                 XFreeEventData(_glfw.x11.display, &event->xcookie);
             }
         }