Reframe swallowed windows if depth doesn't match

X will not allow a window with ParentRelative background to be created
or reparented under a window with mismatching color depth.
Deal with this by destroying the container frame and creating a new one
with the right depth upon swallowing.
Defer destruction of the frame window until after the updated tree has
been rendered to avoid some distracting flickering.

Fixes #3297

include/x.h

@@ -49,6 +49,12 @@ void x_reinit(Con *con);
  */
 void x_con_kill(Con *con);
 
+/*
+ * Completely reinitializes the container's frame, without destroying the old window.
+ *
+ */
+void x_con_reframe(Con *con);
+
 /**
  * Returns true if the client supports the given protocol atom (like WM_DELETE_WINDOW)
  *

src/manage.c

@@ -355,8 +355,16 @@ void manage_window(xcb_window_t window, xcb_get_window_attributes_cookie_t cooki
             }
         }
     }
+    xcb_window_t old_frame = XCB_NONE;
     if (nc->window != cwindow && nc->window != NULL) {
         window_free(nc->window);
+        /* Match frame and window depth. This is needed because X will refuse to reparent a
+         * window whose background is ParentRelative under a window with a different depth. */
+        if (nc->depth != cwindow->depth) {
+            old_frame = nc->frame.id;
+            nc->depth = cwindow->depth;
+            x_con_reframe(nc);
+        }
     }
     nc->window = cwindow;
     x_reinit(nc);
@@ -647,6 +655,12 @@ void manage_window(xcb_window_t window, xcb_get_window_attributes_cookie_t cooki
 
     tree_render();
 
+    /* Destroy the old frame if we had to reframe the container. This needs to be done
+     * after rendering in order to prevent the background from flickering in its place. */
+    if (old_frame != XCB_NONE) {
+        xcb_destroy_window(conn, old_frame);
+    }
+
     /* Windows might get managed with the urgency hint already set (Pidgin is
      * known to do that), so check for that and handle the hint accordingly.
      * This code needs to be in this part of manage_window() because the window

src/x.c

@@ -249,11 +249,7 @@ void x_move_win(Con *src, Con *dest) {
     }
 }
 
-/*
- * Kills the window decoration associated with the given container.
- *
- */
-void x_con_kill(Con *con) {
+static void _x_con_kill(Con *con) {
     con_state *state;
 
     if (con->colormap != XCB_NONE) {
@@ -262,7 +258,6 @@ void x_con_kill(Con *con) {
 
     draw_util_surface_free(conn, &(con->frame));
     draw_util_surface_free(conn, &(con->frame_buffer));
-    xcb_destroy_window(conn, con->frame.id);
     xcb_free_pixmap(conn, con->frame_buffer.id);
     state = state_for_frame(con->frame.id);
     CIRCLEQ_REMOVE(&state_head, state, state);
@@ -275,6 +270,24 @@ void x_con_kill(Con *con) {
     focused_id = last_focused = XCB_NONE;
 }
 
+/*
+ * Kills the window decoration associated with the given container.
+ *
+ */
+void x_con_kill(Con *con) {
+    _x_con_kill(con);
+    xcb_destroy_window(conn, con->frame.id);
+}
+
+/*
+ * Completely reinitializes the container's frame, without destroying the old window.
+ *
+ */
+void x_con_reframe(Con *con) {
+    _x_con_kill(con);
+    x_con_init(con);
+}
+
 /*
  * Returns true if the client supports the given protocol atom (like WM_DELETE_WINDOW)
  *