add xorg PutWindowBelow.

internal/desktop/xorg.go

@@ -113,3 +113,7 @@ func (manager *DesktopManagerCtx) GetKeyboardModifiers() types.KeyboardModifiers
 func (manager *DesktopManagerCtx) GetCursorImage() *types.CursorImage {
 	return xorg.GetCursorImage()
 }
+
+func (manager *DesktopManagerCtx) PutWindowBelow(window uint32) {
+	xorg.PutWindowBelow(window)
+}

internal/desktop/xorg/xorg.c

@@ -136,3 +136,46 @@ XFixesCursorImage *XGetCursorImage(void) {
   Display *display = getXDisplay();
   return XFixesGetCursorImage(display);
 }
+
+void XPutWindowBelow(Window window) {
+  Display *display = getXDisplay();
+  Window root = RootWindow(display, 0);
+
+  // The WM_TRANSIENT_FOR property is defined by the [ICCCM] for managed windows.
+  // This specification extends the use of the property to override-redirect windows.
+  // If an override-redirect is a pop-up on behalf of another window, then the Client
+  // SHOULD set WM_TRANSIENT_FOR on the override-redirect to this other window.
+  //
+  // As an example, a Client should set WM_TRANSIENT_FOR on dropdown menus to the
+  // toplevel application window that contains the menubar.
+
+  // Remove WM_TRANSIENT_FOR
+  Atom WM_TRANSIENT_FOR = XInternAtom(display, "WM_TRANSIENT_FOR", 0);
+  XDeleteProperty(display, window, WM_TRANSIENT_FOR);
+
+  // Add _NET_WM_STATE_BELOW
+  XClientMessageEvent clientMessageEvent;
+  memset(&clientMessageEvent, 0, sizeof(clientMessageEvent));
+
+  // window  = the respective client window
+  // message_type = _NET_WM_STATE
+  // format = 32
+  // data.l[0] = the action, as listed below
+  //   _NET_WM_STATE_REMOVE  0 // remove/unset property
+  //   _NET_WM_STATE_ADD     1 // add/set property
+  //   _NET_WM_STATE_TOGGLE  2 // toggle property 
+  // data.l[1] = first property to alter
+  // data.l[2] = second property to alter
+  // data.l[3] = source indication
+  // other data.l[] elements = 0
+
+  clientMessageEvent.type         = ClientMessage;
+  clientMessageEvent.window       = window;
+  clientMessageEvent.message_type = XInternAtom(display, "_NET_WM_STATE", 0);
+  clientMessageEvent.format       = 32;
+  clientMessageEvent.data.l[0]    = 1;
+  clientMessageEvent.data.l[1]    = XInternAtom(display, "_NET_WM_STATE_BELOW", 0);
+  clientMessageEvent.data.l[3]    = 1;
+
+  XSendEvent(display, root, 0, SubstructureRedirectMask | SubstructureNotifyMask, (XEvent *)&clientMessageEvent);
+}

internal/desktop/xorg/xorg.go

@@ -244,6 +244,13 @@ func GetCursorImage() *types.CursorImage {
 	}
 }
 
+func PutWindowBelow(window uint32) {
+	mu.Lock()
+	defer mu.Unlock()
+
+	C.XPutWindowBelow(C.Window(window))
+}
+
 //export goCreateScreenSize
 func goCreateScreenSize(index C.int, width C.int, height C.int, mwidth C.int, mheight C.int) {
 	ScreenConfigurations[int(index)] = types.ScreenConfiguration{

internal/desktop/xorg/xorg.h

@@ -28,3 +28,5 @@ short XGetScreenRate();
 void XSetKeyboardModifier(int mod, int on);
 char XGetKeyboardModifiers();
 XFixesCursorImage *XGetCursorImage(void);
+
+void XPutWindowBelow(Window window);