xwayland: Don't move window in response to geometry change if state changed

When we leave fullscreen or maximized mode we restore a saved window
position. This is expected, but that saved position was saved when window
geometry was set to have shadows rendered.

Since we restore a saved position that had shadow geometry, we don't want
to move the window when we set geometry again, or we'll move away from the
intended saved position.

I guess this is a counter-proposal to !614

Fixes #454

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>

libweston-desktop/xwayland.c

@@ -64,6 +64,7 @@ struct weston_desktop_xwayland_surface {
 	bool committed;
 	bool added;
 	enum weston_desktop_xwayland_surface_state state;
+	enum weston_desktop_xwayland_surface_state prev_state;
 };
 
 static void
@@ -150,8 +151,16 @@ weston_desktop_xwayland_surface_committed(struct weston_desktop_surface *dsurfac
 
 	if (surface->has_next_geometry) {
 		oldgeom = weston_desktop_surface_get_geometry(surface->surface);
-		sx -= surface->next_geometry.x - oldgeom.x;
+		/* If we're transitioning away from fullscreen or maximized
-		sy -= surface->next_geometry.y - oldgeom.y;
+		 * we've moved to old saved co-ordinates that were saved
+		 * with window geometry in place, so avoid adajusting by
+		 * the geometry in those cases.
+		 */
+		if (surface->state == surface->prev_state) {
+			sx -= surface->next_geometry.x - oldgeom.x;
+			sy -= surface->next_geometry.y - oldgeom.y;
+		}
+		surface->prev_state = surface->state;
 
 		surface->has_next_geometry = false;
 		weston_desktop_surface_set_geometry(surface->surface,