According to the Xlib specification, if the window is WM-managed, the XLowerWindow() function just sends ConfigureRequest event to the WM and "no further processing is performed".

I've got a test that creates three windows: 2 usual window (f1 and f2) and one window (d1) that has the XA_WM_TRANSIENT_FOR property set pointing to the f1 window (see the test code below). Clicking the client area of any of these windows invokes the XLowerWindow() function on that window. Clicking the f2 window does work correctly (the f2 window goes back). Clicking the d1 window does invokes the XLowerWindow() function, but no effect is visible (both f1 and d1 (above the f1 as a transient-for window) stay in the same z-order position not going back under the f2 window). It means that Metacity does not process the ConfigureRequest event properly for windows with XA_WM_TRANSIENT_FOR property set.

The behavior is observed with any Metacity version 2.x including the latest stable one (2.16). However, running the test under any other WM (notably the KWin of KDE) produces correct results (any clicked window goes back (and d1 also pushes the f1 back as well as a transient-for window) according to the XLowerWindow() specification).

The test code:


#include <X11/X.h>
#include <X11/Xlib.h>
#include <X11/Xos.h>
#include <X11/Xutil.h>

#include <stdio.h>

Display *display;
int screen_num;
Window root;

Window create_window(char * name, int x, int y, int width, int height) 
{
    XSizeHints sh;
    XWMHints wmh;
    Window win = XCreateSimpleWindow(display, root, x, y, width, height,
                                     2, // border width
                              BlackPixel(display, screen_num),
                              WhitePixel(display, screen_num));                 
    XStoreName(display, win, name);
    XSelectInput(display, win, ButtonPressMask | KeyPressMask);
    
    sh.width = width;
    sh.height = height;
    sh.x = x;
    sh.y = y;
    sh.flags = USPosition | USSize;
    XSetWMNormalHints(display, win, &sh);

    return win;
}

int main(int argc, char **argv)
{
  Window f1, f2, d1;
  XEvent ev;
  XButtonEvent bev;

  int i, k;

  char *display_name = NULL;
  if ((display = XOpenDisplay(display_name)) == NULL)
  {
    fprintf(stderr, "Couldn't open %s\n", XDisplayName(display_name));
    return -1;
  }
  screen_num = DefaultScreen(display);
  root = RootWindow(display, screen_num);

  f1 = create_window("Frame 1", 100, 100, 200, 200);
  XMapWindow(display, f1);

  f2 = create_window("Frame 2", 400, 100, 200, 200);
  XMapWindow(display, f2);

  d1 = create_window("Dialog 1", 200, 100, 150, 150);
  XMapWindow(display, d1);

  XFlush(display);
  XSync(display, False);

  XSetTransientForHint(display, d1, f1);

  XFlush(display);
  XSync(display, False);

  while (1)
  {
    XNextEvent(display, &ev);
    if (ev.type == ButtonPress)
    {
      bev = ev.xbutton;
      XLowerWindow(display, bev.window);
      XFlush(display);
      XSync(display, True);
    }
  }
}