XReparentWindow works sporadically

问题

I'm experimenting with XReparentWindow with the end goal to aggregate windows of multiple processes into one "cockpit" simulating process. Experiments with XReparentWindow works sporadically~~; sometimes the window is reparented successfully, sometimes not~~. When unsuccessfully reparented the ~~(not)~~ grabbed window flickers for a second and then proceedes as usual, and the grabber show undefined window content. It is successfull every other time (tempted to brute-force the problem away by always trying two times).

Edit 1: Checking output of XQueryTree right after XReparentWindow shows the grabbed window is properly reparented, but would appear to keep its frame origin where grabbed from on display rather than being moved to the grabber window.

The grabbed window is from a real-time OpenGL rendering application, compiled from source. The application does not anticipate the grabbing in any way (maybe it should?). I have also tried grabbing glxgears and a GNOME Terminal, same result.

The experimental code, taking window to grab as program argument (e.g. using xwininfo | grep "Window id"):

#include <X11/Xlib.h>
#include <stdio.h>
#include <assert.h>
#include <unistd.h> // usleep

int main(int argc, char** argv) {
  assert(argc==2);
  Window window, extwin;
  sscanf(argv[1], "%p", &extwin);
  Display* display = XOpenDisplay(0);
  window = XCreateWindow(display, RootWindow(display, 0), 0, 0, 500, 500, 0, DefaultDepth(display, 0), InputOutput, DefaultVisual(display, 0), 0, 0);
  XMapWindow(display, window);
  XReparentWindow(display, extwin, window, 0, 0);
  while(1) {
    XFlush(display);
    usleep(3e5);
  }
  return 0;
}

(Code is manually exported from a restricted environment. Sorry for any typos made during export.)

Looking forward for suggestions of what to try out next.

Edit 2: Having captured the event stream of the grabbed window using xev I notice something odd; after being reparented to the grabber window, it reparents itself back to root window after less than a second (restricted environment, typing what's seen on other window with anticipated significance):

UnmapNotify event ...
ReparentNotify event ... parent 0x4000001 (grabber window)
MapNotify event ...
ConfigureNotify event ... synthetic YES (what is this?)
UnmapNotify event ...
ReparentNotify event ... parent 0xed (reparenting back to parent window, but why?)
MapNotify event ...
VisibilityNotify event ...
Expose event ...
PropertyNotify event ... _NET_WM_DESKTOP state PropertyDelete
PropertyNotify event ... _NET_WM_STATE state PropertyDelete
PropertyNotify event ... WM_STATE state PropertyNewValue

I quit the program and try again a second time, at which the output that continues is:

UnmapNotify event ...
ReparentNotify event ... parent 0x4000001 (grabber window)
MapNotify event ...
VisibilityNotify event ...
Expose event ...

What is going on?

回答1:

I have never tried with an OpenGL application and do not have the environment here. Maybe try first with a simple X app (like xclock) and observe if you get the same behaviour. If yes, that's your code, if no, probably OpenGL interaction.

From your snippset, two comments though:

In the while loop, you should consume the X events

XEvent e;    
while(1) {
     XNextEvent(d, &e);
}

Then the XAddToSaveSet function does not work properly. You will need to use the XFixes in order to properly restore that window in case of a crash.

#include <X11/extensions/Xfixes.h>

...

// The Xorg API is buggy in certain areas.
// Need to use the XFixes extensions to address them
// Initializes these extensions
int event_base_return = 0;
int error_base_return = 0;
Bool result = XFixesQueryExtension(display, &event_base_return);
printf("XFixesQueryExtension result: %d. eventbase: %d - errorbase: %d\n", result, event_base_return, error_base_return);

// We actually only need version 1.0. But if 4.0 is not there then something is really wrong
int major = 4;
int minor = 0;
result = XFixesQueryVersion(display, &major, &minor);
printf("XFixesQueryVersion result: %d - version: %d.%d\n", result, major, minor);

...
XReparentWindow(display, childWindowId, parentWindowId, 0, 0);
XFixesChangeSaveSet(display, childWindowId, SetModeInsert, SaveSetRoot, SaveSetUnmap);
...

回答2:

Brute force solution, grabbing the window repeatedly:

#include <X11/Xlib.h>
#include <stdio.h>
#include <assert.h>
#include <unistd.h> // usleep

int main(int argc, char** argv) {
  assert(argc==2);
  Window window, extwin;
  sscanf(argv[1], "%p", &extwin);
  Display* display = XOpenDisplay(0);
  window = XCreateWindow(display, RootWindow(display, 0), 0, 0, 500, 500, 0, DefaultDepth(display, 0), InputOutput, DefaultVisual(display, 0), 0, 0);
  XMapWindow(display, window);
  while(1) {
    Window root, parent, *ch;
    unsigned int nch;
    XQueryTree(display, extwin, &root, &parent, &ch, &nch);
    if(parent!=window) {
      XReparentWindow(display, extwin, window, 0, 0);
    }
    if(nch>0) { XFree(ch); }
    XFlush(display);
    usleep(3e5);
  }
  return 0;
}

Assuming this only happens once the clause can be disabled after two calls to reparent. Works on my machine. Would appreciate full explaination of what is really going on.

来源：https://stackoverflow.com/questions/54706274/xreparentwindow-works-sporadically

标签

x11

gnome

xlib