backend/x11: correctly update keyboard modifiers

backend/meson.build

@@ -51,6 +51,7 @@ endif
 
 if conf_data.get('WLR_HAS_X11_BACKEND', false)
 	backend_files += files('x11/backend.c')
+	backend_deps += xcb_xkb
 endif
 
 if conf_data.get('WLR_HAS_ELOGIND', false)

backend/x11/backend.c

@@ -16,6 +16,7 @@
 #include <wlr/util/log.h>
 #include <X11/Xlib-xcb.h>
 #include <xcb/xcb.h>
+#include <xcb/xkb.h>
 #ifdef __linux__
 #include <linux/input-event-codes.h>
 #elif __FreeBSD__
@@ -30,6 +31,10 @@ static const struct wlr_backend_impl backend_impl;
 static const struct wlr_output_impl output_impl;
 static const struct wlr_input_device_impl input_device_impl = { 0 };
 
+// TODO: remove global state
+static uint8_t xkb_base_event;
+static uint8_t xkb_base_error;
+
 static uint32_t xcb_button_to_wl(uint32_t button) {
 	switch (button) {
 	case XCB_BUTTON_INDEX_1: return BTN_LEFT;
@@ -157,6 +162,12 @@ static bool handle_x11_event(struct wlr_x11_backend *x11, xcb_generic_event_t *e
 		break;
 	}
 	default:
+		if (event->response_type == xkb_base_event) {
+			xcb_xkb_state_notify_event_t *ev =
+				(xcb_xkb_state_notify_event_t *)event;
+			wlr_keyboard_notify_modifiers(&x11->keyboard, ev->baseMods,
+				ev->latchedMods, ev->lockedMods, ev->lockedGroup);
+		}
 		break;
 	}
 
@@ -225,6 +236,28 @@ static bool wlr_x11_backend_start(struct wlr_backend *backend) {
 		x11->screen->root, 0, 0, 1024, 768, 1, XCB_WINDOW_CLASS_INPUT_OUTPUT,
 		x11->screen->root_visual, mask, values);
 
+	const xcb_query_extension_reply_t *reply =
+		xcb_get_extension_data(x11->xcb_conn, &xcb_xkb_id);
+	if (reply->present) {
+		xkb_base_event = reply->first_event;
+		xkb_base_error = reply->first_error;
+
+		xcb_xkb_use_extension_cookie_t cookie = xcb_xkb_use_extension(
+			x11->xcb_conn, XCB_XKB_MAJOR_VERSION, XCB_XKB_MINOR_VERSION);
+		xcb_xkb_use_extension_reply_t *reply =
+			xcb_xkb_use_extension_reply(x11->xcb_conn, cookie, NULL);
+		if (reply && reply->supported) {
+			xcb_xkb_select_events(x11->xcb_conn,
+				XCB_XKB_ID_USE_CORE_KBD,
+				XCB_XKB_EVENT_TYPE_STATE_NOTIFY,
+				0,
+				XCB_XKB_EVENT_TYPE_STATE_NOTIFY,
+				0,
+				0,
+				0);
+		}
+	}
+
 	output->surf = wlr_egl_create_surface(&x11->egl, &output->win);
 	if (!output->surf) {
 		wlr_log(L_ERROR, "Failed to create EGL surface");

meson.build

@@ -85,6 +85,7 @@ if get_option('enable_x11_backend') or get_option('enable_xwayland')
 	xcb            = dependency('xcb')
 	xcb_composite  = dependency('xcb-composite')
 	xcb_xfixes     = dependency('xcb-xfixes')
+	xcb_xkb        = dependency('xcb-xkb') # TODO: make this optional
 	xcb_image      = dependency('xcb-image')
 	xcb_render     = dependency('xcb-render')
 	x11_xcb        = dependency('x11-xcb')