Following patch adds the ability to switch between displays from a
keybinding
and does not break any old functionality nor default settings.

diff --unified --recursive x2x-1.27.orig/x2x.1 x2x-1.27/x2x.1
--- x2x-1.27.orig/x2x.1 Mon Jan 29 19:08:40 2001
+++ x2x-1.27/x2x.1      Mon Jan 29 19:06:01 2001
@@ -156,6 +156,9 @@
 .TP
 .B \-label \fIlabel\fP
 Override the title of the control window (useful when running over ssh).
+.TP
+.B \-grabkey \fkeysym\fP \fmodifiermask\fP
+Grab a keysym to use for switching between displays.
 .IP
 .SH AUTHOR
 David Chaiken
diff --unified --recursive x2x-1.27.orig/x2x.c x2x-1.27/x2x.c
--- x2x-1.27.orig/x2x.c Mon Jan 29 19:08:40 2001
+++ x2x-1.27/x2x.c      Mon Jan 29 19:08:01 2001
@@ -237,6 +237,9 @@
 static Bool    doBtnBlock   = False;
 static int     nButtons     = 0;
 static KeySym  buttonmap[N_BUTTONS + 1][MAX_BUTTONMAPEVENTS + 1];
+static int     doGrabKey    = 0;
+static KeySym  grabkeysym;
+static unsigned int grabmod = 0;

 /**********
  * main
@@ -268,6 +271,12 @@
     sleep(10);
   } /* END while fromDpy */

+  if (doGrabKey)
+  {
+    XGrabKey(fromDpy,XKeysymToKeycode(fromDpy,grabkeysym),grabmod,
+       DefaultRootWindow(fromDpy),True,GrabModeAsync,GrabModeAsync);
+  }
+
   /* toDpy is always the first shadow */
   pShadow = (PSHADOW)malloc(sizeof(SHADOW));
   pShadow->name = toDpyName;
@@ -496,6 +505,15 @@
       triggerw = atoi(argv[arg]);
     } else if (!strcasecmp(argv[arg], "-copyright")) {
       printf(lawyerese);
+    } else if (!strcasecmp(argv[arg], "-grabkey")) {
+      if (++arg >= argc) Usage();
+      if ((grabkeysym = XStringToKeysym(argv[arg])) == NoSymbol)
+       printf("x2x: warning: can't translate %s\n", argv[arg]);
+      else {
+       if (++arg >= argc) Usage();
+       doGrabKey = 1;
+       grabmod = atoi(argv[arg]);
+      }
     } else {
       Usage();
     } /* END if... */
@@ -525,6 +543,7 @@
   printf("       -sticky <sticky key>\n");
   printf("       -label <LABEL>\n");
   printf("       -buttonmap <button#> \"<keysym> ...\"\n");
+  printf("       -grabkey <keysym> <modifiermask>\n");
   exit(4);

 } /* END Usage */
@@ -997,6 +1016,11 @@
     XSAVECONTEXT(toDpy,   propWin, SelectionClear,
ProcessSelectionClear);
   } /* END if doSel */

+  if (doGrabKey) {
+    XSAVECONTEXT(fromDpy, None, KeyPress,   ProcessKeyEvent);
+    XSAVECONTEXT(fromDpy, None, KeyRelease, ProcessKeyEvent);
+  }
+
 } /* END RegisterEventHandlers */

 static Bool ProcessEvent(dpy, pDpyInfo)
@@ -1010,6 +1034,7 @@
 #define XFINDCONTEXT(A, B, C, D) XFindContext(A, B, C, (XPointer *)(D))

   XNextEvent(dpy, &ev);
+
   handler = 0;
   if ((!XFINDCONTEXT(dpy, pEv->window, pEv->type, &handler)) ||
       (!XFINDCONTEXT(dpy, None, pEv->type, &handler))) {
@@ -1240,7 +1265,7 @@
 #endif
       break;
     } /* END switch button */
-    if (state) { /* then more than one button pressed */
+    if (state && !doGrabKey) { /* then more than one button pressed */
 #ifdef DEBUG
       printf("awaiting button release before disconnecting\n");
 #endif
@@ -1335,6 +1360,19 @@
   for (pSticky = stickies; pSticky; pSticky = pSticky->pNext)
     if (keysym == pSticky->keysym)
       break;
+
+  if (doGrabKey && XKeycodeToKeysym(dpy,pEv->keycode,0) == grabkeysym
+      && pEv->state == grabmod) {
+    if (pEv->type == KeyRelease) {
+      if (pDpyInfo->mode == X2X_DISCONNECTED) {
+       DoConnect(pDpyInfo);
+      } else if (pDpyInfo->mode == X2X_CONNECTED) {
+       DoDisconnect(pDpyInfo);
+      }
+    }
+
+    return False;
+  }

   if (pSticky) {
     for (pShadow = shadows; pShadow; pShadow = pShadow->pNext) {