/* acf4:comp.os.vms / mcmahon@tgv.com (John McMahon) /  8:05 am  Sep 11, 1990 */
/*:In article <1554@front.se>, thomas@front.se (Thomas Thyberg) writes:        */
/* Question:
Is there a way to get the keyboard focus to follow the mouse pointer?

The following program was posted to comp.os.vms a while ago, unfortunately I
have lost the name of the person who provided it.  It provides the "mouse
following focus" that you desire under the DECwindows window manager.
*/

/*

  autofocus.c: Crude hack to do uwm-style focus management.
               Author: (chooses to remain anonymous)

*/
#include <stdio.h>
#ifdef vms
#include <decw$include/X.h>
#include <decw$include/Xlib.h>
#include <decw$include/Xutil.h>
#else
#include <X11/X.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#endif

#define forever           while(1)

static Window GetWMRoot();
static void LowerWindow();
static Window FrameOf();        /* Recursive */
static XWMHints *GetWMHints();  /* Recursive */
static int IgnoreDeadWindow();

main(argc,argv)
   unsigned int argc;
   char *argv[];
{
   Display *display;
   Window wmroot,current,*children,*child,
          focus = 0;
   XWMHints *wmhints;
   int nchildren,i,revert_to;

   /* Open the default display */

   if (!(display = XOpenDisplay(NULL))) {
      fprintf(stderr,"Can't open display\n");
      exit(0);
   }

   /* Find the window manager's pseudo-root window & its children */

   wmroot = GetWMRoot(display,&children,&nchildren);
   XSelectInput(display,wmroot,StructureNotifyMask|
                               SubstructureNotifyMask|
                               KeyPressMask);

   /* Find out which children have set window manager hints */

   for (i = 0, child = children; i < nchildren; ++i, ++child) {
      if (wmhints = GetWMHints(display,*child,&current)) {
         XSelectInput(display,current,EnterWindowMask);
         XFree(wmhints);
      }
   }
   XFree(children);

   /* Ignore error when we try to set focus on a window which has died
      since we received the EnterWindow event */

   XSetErrorHandler(IgnoreDeadWindow);

   /* Grab the function keys used for push & pop */

   XGetInputFocus(display,&focus,&revert_to);

   forever {
      XEvent event;
      XMapEvent *map = (XMapEvent *)&event;
      XEnterWindowEvent *enter = (XEnterWindowEvent *)&event;
      XDestroyWindowEvent *destroy = (XDestroyWindowEvent *)&event;

      XNextEvent(display,&event);
      switch (event.type) {
         case MapNotify: if (wmhints = GetWMHints(display,map->window,
                                                  &current)) {
                            XSelectInput(display,current,EnterWindowMask);
                            XFree(wmhints);
                         }
                         break;

         case EnterNotify: focus = enter->window;
	   		   XSetInputFocus(display,focus,
                                          RevertToPointerRoot,CurrentTime);
                           break;

         case DestroyNotify: if (destroy->window == wmroot) {
                                fprintf(stderr,"Window Manager exited.\n");
                                exit(0);
                             }
      }
   }
}

static XWMHints *GetWMHints(display,window,app_window) /* Recursive */
   Display *display;
   Window window,*app_window;
{
   XWMHints *wmhints;

   if (wmhints = XGetWMHints(display,window)) {
      *app_window = window;
      return wmhints;
   }
   else {
      Window root,parent,*children,*child,current = window;
      int i,nchildren;

      XQueryTree(display,current,&root,&parent,&children,&nchildren);
      for (i = 0, child = children; i < nchildren; ++i, ++child) {
         if (wmhints = GetWMHints(display,*child,app_window)) {
            XFree(children);
            return wmhints;
         }
      }
      if (nchildren) XFree(children);
      return NULL;
   }
}

static Window GetWMRoot(display,children,nchildren)
   Display *display;
   Window **children;
   int *nchildren;
{
   Window window,root,parent,*child;
   XWMHints *wmhints;
   int x,y,width,height,bw,depth,found;
   register int i;

   /* Find first full-screen child of root */

   window = RootWindow(display,DefaultScreen(display));
   found = False;

   forever {
     XQueryTree(display,window,&root,&parent,children,nchildren);
     for (i = 0, child = *children; i < *nchildren; ++i, ++child) {
        XGetGeometry(display,*child,&root,&x,&y,&width,&height,&bw,&depth);
        found = width == DisplayWidth(display,DefaultScreen(display)) &&
                height == DisplayHeight(display,DefaultScreen(display));
        if (found) break;
     }
     if (found) break;
     if (*nchildren) XFree(*children);
     sleep(5);
   }

   /* Find first full-screen child of first full-screen child of root */

   window = *child;
   XFree(*children);
   found = False;

   forever {
     XQueryTree(display,window,&root,&parent,children,nchildren);
     for (i = 0, child = *children; i < *nchildren; ++i, ++child) {
        XGetGeometry(display,*child,&root,&x,&y,&width,&height,&bw,&depth);
        found = width == DisplayWidth(display,DefaultScreen(display)) &&
                height == DisplayHeight(display,DefaultScreen(display));
        if (found) break;
     }
     if (found) break;
     if (*nchildren) XFree(*children);
     sleep(5);
   }

   /* Found window manager's pseudo-root; return it & its children */

   window = *child;
   XFree(*children);
   XQueryTree(display,window,&root,&parent,children,nchildren);
   return window;
}

static int IgnoreDeadWindow(display,error)
   Display *display;
   XErrorEvent *error;
{
   if (error->request_code == 42)  /* Bad Window Id */
      return;
   else XSetErrorHandler(NULL);
}

static Window FrameOf(display,window,wmroot)    /* recursive */
   Display *display;
   Window window,wmroot;
{
   Window root,parent,*children;
   int nchildren;

   XQueryTree(display,window,&root,&parent,&children,&nchildren);
   return parent == wmroot ? window : FrameOf(display,parent,wmroot);
}

static void LowerWindow(display,window)
   Display *display;
   Window window;
{
   XWindowAttributes old;
   XSetWindowAttributes new;

   XGetWindowAttributes(display,window,&old);

   if (!old.override_redirect) {
     new.override_redirect = True;
     XChangeWindowAttributes(display,window,CWOverrideRedirect,&new);
   }

   XLowerWindow(display,window);

   if (!old.override_redirect) {
     new.override_redirect = False;
     XChangeWindowAttributes(display,window,CWOverrideRedirect,&new);
   }
}
/*
John 'Fast-Eddie' McMahon    :    MCMAHON@TGV.COM    : TTTTTTTTTTTTTTTTTTTTTTTT
TGV, Incorporated            :                       :    T   GGGGGGG  V     V
603 Mission Street           : HAVK (abha) Gur bayl  :    T  G          V   V
Santa Cruz, California 95060 : bcrengvat flfgrz gb   :    T  G    GGGG   V V
408-427-4366 or 800-TGV-3440 : or qrfgeblrq ol znvy  :    T   GGGGGGG     V
*/