restack: Add ewmh restacking strategy

Positions the bar window above the _NET_SUPPORTING_WM_CHECK window

The generic restacking strategy now first tries the ewmh strategy, the
the bottom strategy.

include/utils/restack.hpp

@@ -11,8 +11,10 @@ namespace restack_util {
   using params = std::pair<xcb_window_t, xcb_stack_mode_t>;
 
   void restack_relative(connection& conn, xcb_window_t win, xcb_window_t sibling, xcb_stack_mode_t stack_mode);
+  string stack_mode_to_string(xcb_stack_mode_t mode);
   bool are_siblings(connection& conn, xcb_window_t win, xcb_window_t sibling);
   params get_bottom_params(connection& conn, xcb_window_t bar_window);
+  params get_ewmh_params(connection& conn);
   params get_generic_params(connection& conn, xcb_window_t bar_window);
 }
 

include/x11/ewmh.hpp

@@ -53,6 +53,9 @@ namespace ewmh_util {
   void set_wm_window_opacity(xcb_window_t win, unsigned long int values);
 
   vector<xcb_window_t> get_client_list(int screen = 0);
+
+  xcb_window_t get_supporting_wm_check(xcb_window_t win);
+  xcb_window_t get_ewmh_meta_window(xcb_window_t root);
 } // namespace ewmh_util
 
 POLYBAR_NS_END

src/components/bar.cpp

@@ -501,7 +501,9 @@ void bar::restack_window() {
   xcb_stack_mode_t stack_mode = XCB_STACK_MODE_ABOVE;
 
   if (wm_restack == "generic") {
-    std::tie(restack_sibling, stack_mode) = restack_util::get_bottom_params(m_connection, bar_window);
+    std::tie(restack_sibling, stack_mode) = restack_util::get_generic_params(m_connection, bar_window);
+  } else if (wm_restack == "ewmh") {
+    std::tie(restack_sibling, stack_mode) = restack_util::get_ewmh_params(m_connection);
   } else if (wm_restack == "bottom") {
     std::tie(restack_sibling, stack_mode) = restack_util::get_bottom_params(m_connection, bar_window);
   } else if (wm_restack == "bspwm") {
@@ -520,6 +522,8 @@ void bar::restack_window() {
 
   if (restack_sibling != XCB_NONE) {
     try {
+      m_log.info("bar: Restacking bar window relative to %s with stacking mode %s", m_connection.id(restack_sibling),
+          restack_util::stack_mode_to_string(stack_mode));
       restack_util::restack_relative(m_connection, bar_window, restack_sibling, stack_mode);
       m_log.info("Successfully restacked bar window");
     } catch (const exception& err) {

src/utils/restack.cpp

@@ -22,6 +22,23 @@ void restack_relative(connection& conn, xcb_window_t win, xcb_window_t sibling,
   conn.configure_window_checked(win, value_mask, value_list.data());
 }
 
+string stack_mode_to_string(xcb_stack_mode_t mode) {
+  switch (mode) {
+    case XCB_STACK_MODE_ABOVE:
+      return "ABOVE";
+    case XCB_STACK_MODE_BELOW:
+      return "BELOW";
+    case XCB_STACK_MODE_TOP_IF:
+      return "TOP_IF";
+    case XCB_STACK_MODE_BOTTOM_IF:
+      return "BOTTOM_IF";
+    case XCB_STACK_MODE_OPPOSITE:
+      return "OPPOSITE";
+  }
+
+  return "UNKNOWN";
+}
+
 /**
  * @return true iff the two given windows are sibings (are different windows and have same parent).
  */
@@ -40,7 +57,7 @@ bool are_siblings(connection& conn, xcb_window_t win, xcb_window_t sibling) {
  *
  * Moves the bar window to the bottom of the window stack
  */
-std::pair<xcb_window_t, xcb_stack_mode_t> get_bottom_params(connection& conn, xcb_window_t bar_window) {
+params get_bottom_params(connection& conn, xcb_window_t bar_window) {
   auto children = conn.query_tree(conn.root()).children();
   if (children.begin() != children.end() && *children.begin() != bar_window) {
     return {*children.begin(), XCB_STACK_MODE_BELOW};
@@ -49,19 +66,42 @@ std::pair<xcb_window_t, xcb_stack_mode_t> get_bottom_params(connection& conn, xc
   return NONE_PARAMS;
 }
 
+/**
+ * EWMH restack strategy.
+ *
+ * Moves the bar window above the WM meta window (_NET_SUPPORTING_WM_CHECK).
+ * This window is generally towards the bottom of the window stack, but still above other windows that could interfere.
+ *
+ * @see ewmh_util::get_ewmh_meta_window
+ */
+params get_ewmh_params(connection& conn) {
+  if (auto meta_window = ewmh_util::get_ewmh_meta_window(conn.root())) {
+    return {meta_window, XCB_STACK_MODE_ABOVE};
+  }
+
+  return NONE_PARAMS;
+}
+
 /**
  * Generic restack stratgey.
  *
  * Tries to provide the best WM-agnostic restacking.
  *
  * Currently tries to the following stratgies in order:
+ * * ewmh
  * * bottom
  */
-std::pair<xcb_window_t, xcb_stack_mode_t> get_generic_params(connection& conn, xcb_window_t bar_window) {
-  auto [sibling, mode] = get_bottom_params(conn, bar_window);
+params get_generic_params(connection& conn, xcb_window_t bar_window) {
+  auto ewmh_params = get_ewmh_params(conn);
 
-  if (are_siblings(conn, bar_window, sibling)) {
-    return {sibling, mode};
+  if (are_siblings(conn, bar_window, ewmh_params.first)) {
+    return ewmh_params;
+  }
+
+  auto bottom_params = get_bottom_params(conn, bar_window);
+
+  if (are_siblings(conn, bar_window, bottom_params.first)) {
+    return bottom_params;
   }
 
   return NONE_PARAMS;

src/x11/ewmh.cpp

@@ -193,6 +193,39 @@ namespace ewmh_util {
   }
   return {};
 }
+
+/**
+ * Retrieves the _NET_SUPPORTING_WM_CHECK atom on the given window
+ *
+ * @return The _NET_SUPPORTING_WM_CHECK window id or XCB_NONE in case of an error
+ */
+xcb_window_t get_supporting_wm_check(xcb_window_t win) {
+  auto& conn = initialize();
+  xcb_window_t result{};
+  if (xcb_ewmh_get_supporting_wm_check_reply(conn, xcb_ewmh_get_supporting_wm_check(conn, win), &result, nullptr)) {
+    return result;
+  }
+  return XCB_NONE;
+}
+
+/**
+ * Searches for the meta window spawned by the WM to indicate a compliant WM is active.
+ *
+ * The window has the following properties:
+ * * It's pointed to by the root window's _NET_SUPPORTING_WM_CHECK atom
+ * * Its own _NET_SUPPORTING_WM_CHECK atom is set and points to itself
+ *
+ * @return The meta window id or XCB_NONE if it wasn't found
+ */
+xcb_window_t get_ewmh_meta_window(xcb_window_t root) {
+  xcb_window_t wm_meta_window = ewmh_util::get_supporting_wm_check(root);
+
+  if (wm_meta_window != XCB_NONE && ewmh_util::get_supporting_wm_check(wm_meta_window) == wm_meta_window) {
+    return wm_meta_window;
+  }
+
+  return XCB_NONE;
+}
 } // namespace ewmh_util
 
 POLYBAR_NS_END