Advertise struts in _NET_WM_STRUT

Once upon a time, the trigger window was a regular window and could be
arbitrarily stacked. If obscured it would stop working. Later the
trigger window became a dock, to be treated specially by the window
manager. The EWMH spec *suggests* placing docks over all other
windows... but some window managers place docks below before unmapping
them. XMonad is one such window manager. In this case we would like to
advertise struts - reserved space along screen edges that is not
normally obscured. However this should not happen if the dock is already
above all windows. And thus the new '--struts' settings is born, which
uses the '_NET_WM_STRUT' property.

Note that this is a less hacky alternative to '-resurface'.

x2x.c

@@ -236,6 +236,7 @@ typedef struct {
   GC      textGC;
   Atom    wmpAtom, wmdwAtom;
   Atom    netWmWindowTypeAtom, netWmWindowTypeDockAtom;
+  Atom    netWmStrutAtom;
   Cursor  grabCursor;
   Font    fid;
   int     width, height, twidth, theight, tascent;
@@ -379,6 +380,7 @@ static int     compRegLeft  = 0;
 static int     compRegRight = 0;
 static int     compRegUp    = 0;
 static int     compRegLow   = 0;
+static Bool    useStruts    = False;
 
 #ifdef WIN_2_X
 /* These are used to allow pointer comparisons */
@@ -759,6 +761,11 @@ char **argv;
     } else if (!strcasecmp(argv[arg], "-completeregionlow")) {
       if (++arg >= argc) Usage();
       compRegLow = atoi(argv[arg]);
+
+    } else if (!strcasecmp(argv[arg], "-struts")) {
+      useStruts = True;
+
+      debug("will advertise struts in _NET_WM_STRUT\n");
     } else {
       Usage();
     } /* END if... */
@@ -796,6 +803,7 @@ static void Usage()
   printf("       -label <LABEL>\n");
   printf("       -title <TITLE>\n");
   printf("       -buttonmap <button#> \"<keysym> ...\"\n");
+  printf("       -struts\n");
 #ifdef WIN_2_X
   printf("       -offset [-]<pixel offset of \"to\">\n");
   printf("WIN_2_X build allows Windows or X as -from display\n");
@@ -1216,6 +1224,18 @@ PDPYINFO pDpyInfo;
                     XA_ATOM, 32, PropModeReplace,
                     (unsigned char *)&pDpyInfo->netWmWindowTypeDockAtom, 1);
 
+    if (useStruts) {
+      unsigned long struts[4] = { doEdge == EDGE_WEST ? triggerw : 0
+                                , doEdge == EDGE_EAST ? triggerw : 0
+                                , doEdge == EDGE_NORTH ? triggerw : 0
+                                , doEdge == EDGE_SOUTH ? triggerw : 0
+                                };
+      pDpyInfo->netWmStrutAtom = XInternAtom(fromDpy, "_NET_WM_STRUT", True);
+      XChangeProperty(fromDpy, trigger, pDpyInfo->netWmStrutAtom,
+                      XA_CARDINAL, 32, PropModeReplace,
+                      (unsigned char *)&struts, 4);
+    }
+
 #ifdef WIN_2_X
     }
 #endif