#include <X11/X.h>                      // for Window, Atom, None#include <X11/Xlib.h>                   // for XGetSelectionOwner, XInternAtom#include <X11/extensions/Xcomposite.h>  // for XCompositeGetOverlayWindow#include <stdio.h>                      // for printf, snprintf, fflush, stdout#include <stdlib.h>                     // for system void DumpWindow(const char *title, Window w) {  printf("# %s window = %#llx\n", title, (unsigned long long)w);  if (w == None) {    return;  }   // Lots of hackery to dump all we know about this window.  char buf[128];  buf[sizeof(buf) - 1] = 0;  snprintf(buf, sizeof(buf) - 1, "xwininfo -all -id %#llx",           (unsigned long long)w);  printf("$ %s\n", buf);  fflush(stdout);  system(buf);  snprintf(buf, sizeof(buf) - 1, "xprop -id %#llx", (unsigned long long)w);  printf("$ %s\n", buf);  fflush(stdout);  system(buf);  snprintf(      buf, sizeof(buf) - 1,      "ps \"$(xprop -id %#llx _NET_WM_PID | cut -d ' ' -f 3)\" 2>/dev/null",      (unsigned long long)w);  printf("$ %s\n", buf);  fflush(stdout);  system(buf);  if (((unsigned long long)w) >> 16 != 0) {    // Lists all other windows from the same X11 client.    snprintf(        buf, sizeof(buf) - 1,        "xwininfo -root -tree | grep '%#llx[0-9a-f][0-9a-f][0-9a-f][0-9a-f] '",        ((unsigned long long)w) >> 16);    printf("$ %s\n", buf);    fflush(stdout);    system(buf);  }} int main() {  Display *display = XOpenDisplay(NULL);  if (display == NULL) {    fprintf(stderr, "Could not connect to $DISPLAY.\n");    return 1;  }  char buf[64];  snprintf(buf, sizeof(buf), "_NET_WM_CM_S%d", (int)DefaultScreen(display));  buf[sizeof(buf) - 1] = 0;  Atom atom = XInternAtom(display, buf, False);  DumpWindow(buf, XGetSelectionOwner(display, atom));   Window cow = XCompositeGetOverlayWindow(display, DefaultRootWindow(display));  // Instantly release to prevent black screen with compton --backend glx.  XCompositeReleaseOverlayWindow(display, cow);  DumpWindow("Composite overlay", cow);   return 0;}