Set the _NET_WM_STATE_HIDDEN atom on windows that are currently not visible due to being in the non-focused tab of a stacked or tabbed container.

fixes #1648

include/atoms.xmacro

@@ -5,6 +5,7 @@ xmacro(_NET_WM_MOVERESIZE)
 xmacro(_NET_WM_STATE_FULLSCREEN)
 xmacro(_NET_WM_STATE_DEMANDS_ATTENTION)
 xmacro(_NET_WM_STATE_MODAL)
+xmacro(_NET_WM_STATE_HIDDEN)
 xmacro(_NET_WM_STATE)
 xmacro(_NET_WM_WINDOW_TYPE)
 xmacro(_NET_WM_WINDOW_TYPE_NORMAL)

src/ewmh.c

@@ -234,6 +234,6 @@ void ewmh_setup_hints(void) {
     /* I’m not entirely sure if we need to keep _NET_WM_NAME on root. */
     xcb_change_property(conn, XCB_PROP_MODE_REPLACE, root, A__NET_WM_NAME, A_UTF8_STRING, 8, strlen("i3"), "i3");
 
-    /* only send the first 29 atoms (last one is _NET_CLOSE_WINDOW) increment that number when adding supported atoms */
-    xcb_change_property(conn, XCB_PROP_MODE_REPLACE, root, A__NET_SUPPORTED, XCB_ATOM_ATOM, 32, 29, supported_atoms);
+    /* only send the first 30 atoms (last one is _NET_CLOSE_WINDOW) increment that number when adding supported atoms */
+    xcb_change_property(conn, XCB_PROP_MODE_REPLACE, root, A__NET_SUPPORTED, XCB_ATOM_ATOM, 32, 30, supported_atoms);
 }

src/x.c

@@ -36,6 +36,7 @@ typedef struct con_state {
     bool mapped;
     bool unmap_now;
     bool child_mapped;
+    bool is_hidden;
 
     /** The con for which this state is. */
     Con *con;
@@ -611,6 +612,33 @@ void x_deco_recurse(Con *con) {
         x_draw_decoration(con);
 }
 
+/*
+ * Sets or removes the _NET_WM_STATE_HIDDEN property on con if necessary.
+ *
+ */
+static void set_hidden_state(Con *con) {
+    if (con->window == NULL) {
+        return;
+    }
+
+    con_state *state = state_for_frame(con->frame);
+    bool should_be_hidden = con_is_hidden(con);
+    if (should_be_hidden == state->is_hidden)
+        return;
+
+    unsigned int num = 0;
+    uint32_t values[1];
+    if (should_be_hidden) {
+        DLOG("setting _NET_WM_STATE_HIDDEN for con = %p\n", con);
+        values[num++] = A__NET_WM_STATE_HIDDEN;
+    } else {
+        DLOG("removing _NET_WM_STATE_HIDDEN for con = %p\n", con);
+    }
+
+    xcb_change_property(conn, XCB_PROP_MODE_REPLACE, con->window->id, A__NET_WM_STATE, XCB_ATOM_ATOM, 32, num, values);
+    state->is_hidden = should_be_hidden;
+}
+
 /*
  * This function pushes the properties of each node of the layout tree to
  * X11 if they have changed (like the map state, position of the window, …).
@@ -814,6 +842,8 @@ void x_push_node(Con *con) {
         fake_absolute_configure_notify(con);
     }
 
+    set_hidden_state(con);
+
     /* Handle all children and floating windows of this node. We recurse
      * in focus order to display the focused client in a stack first when
      * switching workspaces (reduces flickering). */