compositor-x11: Use XKB StateNotify to synchronise state

Make sure that we always have the exact same view of the keyboard state
as the host server by using XKB StateNotify events to update our state
exactly rather than relying on key events.  In particular, this fixes
key state during grabs, where we either miss modifiers completely or get
them stuck permanently, depending on the nature of the grab and the
implementation of the X window manager/compositor.

The downside, however, is that Weston wakes up on every modifier change,
regardless of whether or not it has focus.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>

src/compositor-x11.c

@@ -149,6 +149,7 @@ x11_compositor_setup_xkb(struct x11_compositor *c)
 #else
 	const xcb_query_extension_reply_t *ext;
 	xcb_generic_error_t *error;
+	xcb_void_cookie_t select;
 	xcb_xkb_per_client_flags_cookie_t pcf;
 	xcb_xkb_per_client_flags_reply_t *pcf_reply;
 
@@ -162,6 +163,20 @@ x11_compositor_setup_xkb(struct x11_compositor *c)
 	}
 	c->xkb_event_base = ext->first_event;
 
+	select = xcb_xkb_select_events(c->conn,
+				       XCB_XKB_ID_USE_CORE_KBD,
+				       XCB_XKB_EVENT_TYPE_STATE_NOTIFY,
+				       0,
+				       XCB_XKB_EVENT_TYPE_STATE_NOTIFY,
+				       0,
+				       0,
+				       NULL);
+	error = xcb_request_check(c->conn, select);
+	if (error) {
+		weston_log("error: failed to select for XKB state events\n");
+		return;
+	}
+
 	pcf = xcb_xkb_per_client_flags(c->conn,
 				       XCB_XKB_ID_USE_CORE_KBD,
 				       XCB_XKB_PER_CLIENT_FLAG_DETECTABLE_AUTO_REPEAT,
@@ -595,6 +610,51 @@ x11_compositor_find_output(struct x11_compositor *c, xcb_window_t window)
 	return NULL;
 }
 
+#ifdef HAVE_XCB_XKB
+static uint32_t
+get_xkb_mod_mask(struct x11_compositor *c, uint32_t in)
+{
+	struct weston_xkb_info *info = &c->base.seat->xkb_info;
+	uint32_t ret = 0;
+
+	if ((in & ShiftMask) && info->shift_mod != XKB_MOD_INVALID)
+		ret |= (1 << info->shift_mod);
+	if ((in & LockMask) && info->caps_mod != XKB_MOD_INVALID)
+		ret |= (1 << info->caps_mod);
+	if ((in & ControlMask) && info->ctrl_mod != XKB_MOD_INVALID)
+		ret |= (1 << info->ctrl_mod);
+	if ((in & Mod1Mask) && info->alt_mod != XKB_MOD_INVALID)
+		ret |= (1 << info->alt_mod);
+	if ((in & Mod2Mask) && info->mod2_mod != XKB_MOD_INVALID)
+		ret |= (1 << info->mod2_mod);
+	if ((in & Mod3Mask) && info->mod3_mod != XKB_MOD_INVALID)
+		ret |= (1 << info->mod3_mod);
+	if ((in & Mod4Mask) && info->super_mod != XKB_MOD_INVALID)
+		ret |= (1 << info->super_mod);
+	if ((in & Mod5Mask) && info->mod5_mod != XKB_MOD_INVALID)
+		ret |= (1 << info->mod5_mod);
+
+	return ret;
+}
+
+static void
+update_xkb_state(struct x11_compositor *c, xcb_xkb_state_notify_event_t *state)
+{
+	struct weston_compositor *ec = &c->base;
+	struct wl_seat *seat = &ec->seat->seat;
+
+	xkb_state_update_mask(c->base.seat->xkb_state.state,
+			      get_xkb_mod_mask(c, state->baseMods),
+			      get_xkb_mod_mask(c, state->latchedMods),
+			      get_xkb_mod_mask(c, state->lockedMods),
+			      0,
+			      0,
+			      state->group);
+
+	notify_modifiers(seat, wl_display_next_serial(c->base.wl_display));
+}
+#endif
+
 static void
 x11_compositor_deliver_button_event(struct x11_compositor *c,
 				    xcb_generic_event_t *event, int state)
@@ -755,6 +815,7 @@ x11_compositor_handle_event(int fd, uint32_t mask, void *data)
 				   weston_compositor_get_time(),
 				   key_press->detail - 8,
 				   WL_KEYBOARD_KEY_STATE_PRESSED,
+				   c->has_xkb ? STATE_UPDATE_NONE :
 						STATE_UPDATE_AUTOMATIC);
 			break;
 		case XCB_KEY_RELEASE:
@@ -769,7 +830,7 @@ x11_compositor_handle_event(int fd, uint32_t mask, void *data)
 				   weston_compositor_get_time(),
 				   key_release->detail - 8,
 				   WL_KEYBOARD_KEY_STATE_RELEASED,
-				   STATE_UPDATE_AUTOMATIC);
+				   STATE_UPDATE_NONE);
 			break;
 		case XCB_BUTTON_PRESS:
 			x11_compositor_deliver_button_event(c, event, 1);
@@ -840,6 +901,16 @@ x11_compositor_handle_event(int fd, uint32_t mask, void *data)
 			break;
 		}
 
+#ifdef HAVE_XCB_XKB
+		if (c->has_xkb &&
+		    (event->response_type & ~0x80) == c->xkb_event_base) {
+			xcb_xkb_state_notify_event_t *state =
+				(xcb_xkb_state_notify_event_t *) event;
+			if (state->xkbType == XCB_XKB_STATE_NOTIFY)
+				update_xkb_state(c, state);
+		}
+#endif
+
 		count++;
 		if (prev != event)
 			free (event);