path: root/driver/screens.c

/* screens.c --- dealing with RANDR, Xinerama, and VidMode Viewports.
 * xscreensaver, Copyright © 1991-2021 Jamie Zawinski <jwz@jwz.org>
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that
 * copyright notice and this permission notice appear in supporting
 * documentation.  No representations are made about the suitability of this
 * software for any purpose.  It is provided "as is" without express or 
 * implied warranty.
 */

/*   There are a bunch of different mechanisms for multiple monitors
 *   available in X.  XScreenSaver needs to care about this for two reasons:
 *   first, to ensure that all visible areas go black; and second, so that
 *   the windows of screen savers exactly fill the glass of each monitor
 *   (instead of one saver spanning multiple monitors, or a monitor
 *   displaying only a sub-rectangle of the screen saver.)
 *
 *   1) Multi-screen:
 *
 *      This is the original way.  Each monitor gets its own display number.
 *      ":0.0" is the first one, ":0.1" is the next, and so on.  The value
 *      of $DISPLAY determines which screen windows open on by default.  A
 *      single app can open windows on multiple screens with the same
 *      display connection, but windows cannot be moved from one screen to
 *      another.  The mouse can be moved from one screen to another, though.
 *      Screens may be different depths (e.g., one can be TrueColor and one
 *      can be PseudoColor.)  Screens cannot be resized or moved without
 *      restarting X.
 *
 *      Everyone hates this way of doing things because of the inability to
 *      move a window from one screen to another without restarting the
 *      application.
 *
 *   2) Xinerama:
 *
 *      There is a single giant root window that spans all the monitors.
 *      All monitors are the same depth, and windows can be moved around.
 *      Applications can learn which rectangles are actually visible on
 *      monitors by querying the Xinerama server extension.  (If you don't
 *      do that, you end up with dialog boxes that try to appear in the
 *      middle of the screen actually spanning the gap between two
 *      monitors.)
 *
 *      Xinerama didn't? work with DRI, which means that Xinerama precluded
 *      hardware acceleration in OpenGL programs.  Also, screens couldn't
 *      be resized or moved without restarting X.
 *
 *   3) Vidmode Viewports:
 *
 *      No longer supported as of XScreenSaver 6.
 *
 *      With this extension, the root window can be bigger than the
 *      monitor.  Moving the mouse near the edges of the screen scrolls
 *      around, like a pan-and-scan movie.  There was also a hot-key for
 *      changing the monitor's resolution (zooming in/out).
 *
 *      Trying to combine this with Xinerama crashes the server, so you
 *      could only use this if you had only a single screen, or were in old
 *      multi-screen mode.
 *
 *      Also, half the time it didn't work at all: it tended to lie about
 *      the size of the rectangle in use.
 *
 *   4) RANDR 1.0:
 *
 *      The first version of the "Resize and Rotate" extension let you
 *      change the resolution of a screen on the fly.  The root window
 *      would actually resize.  However, it was also incompatible with
 *      Xinerama (did it crash, or just do nothing? I can't remember) so
 *      you needed to be in single-screen or old multi-screen mode.  I
 *      believe RANDR could co-exist with Vidmode Viewports, but I'm not
 *      sure.
 *
 *   5) RANDR 1.2:
 *
 *      Finally, RANDR added the functionality of Xinerama, plus some.
 *      Each X screen (in the sense of #1, "multi-screen") can have a
 *      number of sub-rectangles that are displayed on monitors, and each
 *      of those sub-rectangles can be displayed on more than one monitor.
 *      So it's possible (I think) to have a hybrid of multi-screen and
 *      Xinerama (e.g., to have two monitors running in one depth, and
 *      three monitors running in another?)  Typically though, there will
 *      be a single X screen with one giant root window underlying the
 *      rectangles of multiple monitors.  Also everything is dynamic:
 *      monitors can be added, removed, and resized at runtime, with
 *      notification events.
 *
 *      RANDR rectangles can overlap, meaning one monitor can mirror
 *      another, or show a sub-rectangle of another, or just overlap in
 *      strange ways.  The proper way to respond to weird layouts is... not
 *      always obvious.
 *
 *      Also sometimes RANDR says stupid shit like, "You have one screen,
 *      and it has no available sizes or orientations."
 *
 *      Sometimes RANDR and Xinerama report the same info, and sometimes
 *      not, so we look at both and see which looks most plausible.
 *
 *      Also, Nvidia fucked it up: their drivers that were popular in 2008,
 *      when running in "TwinView" mode, reported correct sizes via
 *      Xinerama, but reported one giant screen via RANDR.  Nvidia's
 *      response was, "We don't support RANDR, use Xinerama instead", which
 *      is another reason that XScreenSaver historically had to query both
 *      extensions and make a guess.  Maybe this is no longer necessary.
 */

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <X11/Xlib.h>

#ifndef HAVE_RANDR_12
# undef HAVE_RANDR  /* RANDR 1.1 is no longer supported */
#endif

#ifdef HAVE_RANDR
# include <X11/extensions/Xrandr.h>
#endif /* HAVE_RANDR */

#ifdef HAVE_XINERAMA
# include <X11/extensions/Xinerama.h>
#endif /* HAVE_XINERAMA */

#ifdef HAVE_XF86VMODE
# include <X11/extensions/xf86vmode.h>
#endif /* HAVE_XF86VMODE */

#include "blurb.h"
#include "screens.h"

#undef countof
#define countof(x) (sizeof((x))/sizeof((*x)))


void
free_monitors (monitor **monitors)
{
  monitor **m2 = monitors;
  if (! monitors) return;
  while (*m2) 
    {
      if ((*m2)->desc) free ((*m2)->desc);
      if ((*m2)->err) free ((*m2)->err);
      free (*m2);
      m2++;
    }
  free (monitors);
}


static char *
append (char *s1, const char *s2)
{
  char *s = (char *) malloc ((s1 ? strlen(s1) : 0) +
                             (s2 ? strlen(s2) : 0) + 3);
  *s = 0;
  if (s1) strcat (s, s1);
  if (s1 && s2) strcat (s, "\n");
  if (s2) strcat (s, s2);
  if (s1) free (s1);
  return s;
}


#ifdef HAVE_XINERAMA

static monitor **
xinerama_scan_monitors (Display *dpy, char **errP)
{
  Screen *screen = DefaultScreenOfDisplay (dpy);
  int event, error, nscreens, i;
  XineramaScreenInfo *xsi;
  monitor **monitors;

  if (! XineramaQueryExtension (dpy, &event, &error))
    return 0;

  if (! XineramaIsActive (dpy)) 
    return 0;

  xsi = XineramaQueryScreens (dpy, &nscreens);
  if (!xsi) return 0;

  monitors = (monitor **) calloc (nscreens + 1, sizeof(*monitors));
  if (!monitors) return 0;

  for (i = 0; i < nscreens; i++)
    {
      monitor *m = (monitor *) calloc (1, sizeof (monitor));
      monitors[i] = m;
      m->id       = i;
      m->screen   = screen;
      m->x        = xsi[i].x_org;
      m->y        = xsi[i].y_org;
      m->width    = xsi[i].width;
      m->height   = xsi[i].height;
    }
  return monitors;
}

#endif /* HAVE_XINERAMA */


#ifdef HAVE_RANDR

static monitor **
randr_scan_monitors (Display *dpy, char **errP)
{
  int event, error, major, minor, nscreens, i, j;
  monitor **monitors;

  if (! XRRQueryExtension (dpy, &event, &error))
    return 0;

  if (! XRRQueryVersion (dpy, &major, &minor))
    return 0;

  if (! (major > 1 || (major == 1 && minor >= 2)))
    return 0;  /* 1.2 ir newer is required */

  /* Add up the virtual screens on each X screen. */
  nscreens = 0;
  for (i = 0; i < ScreenCount (dpy); i++)
    {
      XRRScreenResources *res =
        XRRGetScreenResources (dpy, RootWindow (dpy, i));
      nscreens += res->noutput;
      XRRFreeScreenResources (res);
    }

  if (nscreens <= 0)
    {
      *errP = append (*errP,
                      "WARNING: RANDR reported no screens!  Ignoring it.");
      return 0;
    }

  monitors = (monitor **) calloc (nscreens + 1, sizeof(*monitors));
  if (!monitors) return 0;

  for (i = 0, j = 0; i < ScreenCount (dpy); i++)
    {
      Screen *screen = ScreenOfDisplay (dpy, i);
      int k;
      XRRScreenResources *res = 
        XRRGetScreenResources (dpy, RootWindowOfScreen (screen));
      for (k = 0; k < res->noutput; k++, j++)
        {
          monitor *m = (monitor *) calloc (1, sizeof (monitor));
          XRROutputInfo *rroi = XRRGetOutputInfo (dpy, res, 
                                                  res->outputs[k]);
          RRCrtc crtc = (rroi->crtc  ? rroi->crtc :
                         rroi->ncrtc ? rroi->crtcs[0] : 0);
          XRRCrtcInfo *crtci = (crtc ? XRRGetCrtcInfo(dpy, res, crtc) : 0);

          monitors[j] = m;
          m->screen   = screen;
          m->id       = (i * 1000) + j;
          m->desc     = (rroi->name ? strdup (rroi->name) : 0);

          if (crtci)
            {
              /* Note: if the screen is rotated, XRRConfigSizes contains
                 the unrotated WxH, but XRRCrtcInfo contains rotated HxW.
               */
              m->x      = crtci->x;
              m->y      = crtci->y;
              m->width  = crtci->width;
              m->height = crtci->height;
            }

          if (rroi->connection == RR_Disconnected)
            m->sanity = S_DISABLED;
          /* #### do the same for RR_UnknownConnection? */

          if (crtci) 
            XRRFreeCrtcInfo (crtci);
          XRRFreeOutputInfo (rroi);
        }
      XRRFreeScreenResources (res);
    }

  /* Work around more fucking brain damage. */
  {
    int ok = 0;
    int i = 0;
    while (monitors[i]) 
      {
        if (monitors[i]->width != 0 && monitors[i]->height != 0)
          ok++;
        i++;
      }
    if (! ok)
      {
        *errP = append (*errP,
              "WARNING: RANDR says all screens are 0x0!  Ignoring it.");
        free_monitors (monitors);
        monitors = 0;
      }
  }

  return monitors;
}

#endif /* HAVE_RANDR */


static monitor **
basic_scan_monitors (Display *dpy, char **errP)
{
  int nscreens = ScreenCount (dpy);
  int i;
  monitor **monitors = (monitor **) calloc (nscreens + 1, sizeof(*monitors));
  if (!monitors) return 0;

  for (i = 0; i < nscreens; i++)
    {
      Screen *screen = ScreenOfDisplay (dpy, i);
      monitor *m = (monitor *) calloc (1, sizeof (monitor));
      monitors[i] = m;
      m->id       = i;
      m->screen   = screen;
      m->x        = 0;
      m->y        = 0;
      m->width    = WidthOfScreen (screen);
      m->height   = HeightOfScreen (screen);
    }
  return monitors;
}


#if defined(HAVE_RANDR) && defined(HAVE_XINERAMA)

/*   From: Aaron Plattner <aplattner@nvidia.com>
     Date: August 7, 2008 10:21:25 AM PDT
     To: linux-bugs@nvidia.com

     The NVIDIA X driver does not yet support RandR 1.2.  The X server has
     a compatibility layer in it that allows RandR 1.2 clients to talk to
     RandR 1.1 drivers through an RandR 1.2 pseudo-output called "default".
     This reports the total combined resolution of the TwinView display,
     since it doesn't have any visibility into TwinView metamodes.  There
     is no way for the driver to prevent the server from turning on this
     compatibility layer.

     The intention is for X client applications to continue to use the
     Xinerama extension to query the screen geometry.  RandR 1.2 reports
     its own Xinerama info for this purpose.  I would recommend against
     modifying xscreensaver to try to get this information from RandR.
 */
static monitor **
randr_versus_xinerama_fight (Display *dpy, monitor **randr_monitors, 
                             char **errP)
{
  monitor **xinerama_monitors;

  if (!randr_monitors) 
    return 0;

  xinerama_monitors = xinerama_scan_monitors (dpy, errP);
  if (!xinerama_monitors)
    return randr_monitors;

  if (! monitor_layouts_differ_p (randr_monitors, xinerama_monitors))
    {
      free_monitors (xinerama_monitors);
      return randr_monitors;
    }
  else if (   randr_monitors[0] &&   !randr_monitors[1] &&  /* 1 monitor */
           xinerama_monitors[0] && xinerama_monitors[1])    /* >1 monitor */
    {
      *errP = append (*errP,
                      "WARNING: RANDR reports 1 screen but Xinerama\n"
                      "         reports multiple.  Believing Xinerama.");
      free_monitors (randr_monitors);
      return xinerama_monitors;
    }
  else
    {
      *errP = append (*errP,  /* This is "normal" now, I guess. */
                      "RANDR and Xinerama report different screen layouts");
      free_monitors (xinerama_monitors);
      return randr_monitors;
    }
}

#endif /* HAVE_RANDR && HAVE_XINERAMA */


#ifdef DEBUG_MULTISCREEN

/* If DEBUG_MULTISCREEN is defined, then in "-debug" mode, xscreensaver
   will pretend that it is changing the number of connected monitors
   every few seconds, using the geometries in the following list,
   for stress-testing purposes.
 */
static monitor **
debug_scan_monitors (Display *dpy, char **errP)
{
  static const char * const geoms[] = {
    "1600x1028+0+22",
    "1024x768+0+22",
    "800x600+0+22",
    "800x600+0+22,800x600+800+22",
    "800x600+0+22,800x600+800+22,800x600+300+622",
    "800x600+0+22,800x600+800+22,800x600+0+622,800x600+800+622",
    "640x480+0+22,640x480+640+22,640x480+0+502,640x480+640+502",
    "640x480+240+22,640x480+0+502,640x480+640+502",
    "640x480+0+200,640x480+640+200",
    "800x600+400+22",
    "320x200+0+22,320x200+320+22,320x200+640+22,320x200+960+22,320x200+0+222,320x200+320+222,320x200+640+222,320x200+960+222,320x200+0+422,320x200+320+422,320x200+640+422,320x200+960+422,320x200+0+622,320x200+320+622,320x200+640+622,320x200+960+622,320x200+0+822,320x200+320+822,320x200+640+822,320x200+960+822"
  };
  static int index = 0;
  monitor **monitors = (monitor **) calloc (100, sizeof(*monitors));
  int nscreens = 0;
  Screen *screen = DefaultScreenOfDisplay (dpy);

  char *s = strdup (geoms[index]);
  char *token = strtok (s, ",");
  while (token)
    {
      monitor *m = calloc (1, sizeof (monitor));
      char c;
      m->id = nscreens;
      m->screen = screen;
      if (4 != sscanf (token, "%dx%d+%d+%d%c", 
                       &m->width, &m->height, &m->x, &m->y, &c))
        abort();
      m->width -= 2;
      m->height -= 2;
      monitors[nscreens++] = m;
      token = strtok (0, ",");
    }
  free (s);
  
  index = (index+1) % countof(geoms);
  return monitors;
}
#endif /* DEBUG_MULTISCREEN */


#ifdef QUAD_MODE
static monitor **
quadruple (monitor **monitors, Bool debug_p, char **errP)
{
  int i, j, count = 0;
  monitor **monitors2;
  while (monitors[count])
    count++;
  monitors2 = (monitor **) calloc (count * 4 + 1, sizeof(*monitors));
  if (!monitors2) abort();

  for (i = 0, j = 0; i < count; i++)
    {
      int k;
      for (k = 0; k < 4; k++)
        {
          monitors2[j+k] = (monitor *) calloc (1, sizeof (monitor));
          *monitors2[j+k] = *monitors[i];
          monitors2[j+k]->width  /= (debug_p ? 4 : 2);
          monitors2[j+k]->height /= 2;
          monitors2[j+k]->id = (monitors[i]->id * 4) + k;
          monitors2[j+k]->name = (monitors[i]->name
                                  ? strdup (monitors[i]->name) : 0);
        }
      monitors2[j+1]->x += monitors2[j]->width;
      monitors2[j+2]->y += monitors2[j]->height;
      monitors2[j+3]->x += monitors2[j]->width;
      monitors2[j+3]->y += monitors2[j]->height;
      j += 4;
    }

  free_monitors (monitors);
  return monitors2;
}
#endif /* QUAD_MODE */


monitor **
scan_monitors (Display *dpy)
{
  monitor **monitors = 0;
  char *err = 0;

# ifdef DEBUG_MULTISCREEN
    if (! monitors) monitors = debug_scan_monitors (dpy, &err);
# endif

# ifdef HAVE_RANDR
    if (! monitors) monitors = randr_scan_monitors (dpy, &err);

#  ifdef HAVE_XINERAMA
   monitors = randr_versus_xinerama_fight (dpy, monitors, &err);
#  endif
# endif /* HAVE_RANDR */

# ifdef HAVE_XINERAMA
  if (! monitors) monitors = xinerama_scan_monitors (dpy, &err);
# endif

  if (! monitors) monitors = basic_scan_monitors (dpy, &err);

# ifdef QUAD_MODE
  if (p->quad_p)
    monitors = quadruple (monitors, p->debug_p, &err);
# endif

  if (monitors && *monitors && err) monitors[0]->err = err;

  return monitors;
}


static Bool
monitors_overlap_p (monitor *a, monitor *b)
{
  /* Two rectangles overlap if the max of the tops is less than the
     min of the bottoms and the max of the lefts is less than the min
     of the rights.
   */
# undef MAX
# undef MIN
# define MAX(A,B) ((A)>(B)?(A):(B))
# define MIN(A,B) ((A)<(B)?(A):(B))

  int maxleft  = MAX(a->x, b->x);
  int maxtop   = MAX(a->y, b->y);
  int minright = MIN(a->x + a->width  - 1, b->x + b->width);
  int minbot   = MIN(a->y + a->height - 1, b->y + b->height);
  return (maxtop < minbot && maxleft < minright);
}


static Bool
plausible_aspect_ratio_p (monitor **monitors)
{
  /* Modern wide-screen monitors come in the following aspect ratios:

            One monitor:        If you tack a 640x480 monitor
                                onto the right, the ratio is:
         16 x 9    --> 1.78
        852 x 480  --> 1.77        852+640 x 480  --> 3.11      "SD 480p"
       1280 x 720  --> 1.78       1280+640 x 720  --> 2.67      "HD 720p"
       1280 x 920  --> 1.39       1280+640 x 920  --> 2.09
       1366 x 768  --> 1.78       1366+640 x 768  --> 2.61      "HD 768p"
       1440 x 900  --> 1.60       1440+640 x 900  --> 2.31
       1680 x 1050 --> 1.60       1680+640 x 1050 --> 2.21
       1690 x 1050 --> 1.61       1690+640 x 1050 --> 2.22
       1920 x 1080 --> 1.78       1920+640 x 1080 --> 2.37      "HD 1080p"
       1920 x 1200 --> 1.60       1920+640 x 1200 --> 2.13
       2560 x 1600 --> 1.60       2560+640 x 1600 --> 2.00

     So that implies that if we ever see an aspect ratio >= 2.0,
     we can be pretty sure that the X server is lying to us, and
     that's actually two monitors, not one.
   */
  if (monitors[0] && !monitors[1] &&    /* exactly 1 monitor */
      monitors[0]->height &&
      monitors[0]->width / (double) monitors[0]->height >= 1.9)
    return False;
  else
    return True;
}


/* Mark the ones that overlap, etc.
 */
void
check_monitor_sanity (monitor **monitors)
{
  int i, j, count = 0;

  while (monitors[count])
    count++;

#  define X1 monitors[i]->x
#  define X2 monitors[j]->x
#  define Y1 monitors[i]->y
#  define Y2 monitors[j]->y
#  define W1 monitors[i]->width
#  define W2 monitors[j]->width
#  define H1 monitors[i]->height
#  define H2 monitors[j]->height

  /* If a monitor is enclosed by any other monitor, that's insane.
   */
  for (i = 0; i < count; i++)
    for (j = 0; j < count; j++)
      if (i != j &&
          monitors[i]->sanity == S_SANE &&
          monitors[j]->sanity == S_SANE &&
          monitors[i]->screen == monitors[j]->screen &&
          X2 >= X1 &&
          Y2 >= Y1 &&
          (X2+W2) <= (X1+W1) &&
          (Y2+H2) <= (Y1+H1))
        {
          if (X1 == X2 &&
              Y1 == Y2 &&
              W1 == W2 &&
              H1 == H2)
            monitors[j]->sanity = S_DUPLICATE;
          else 
            monitors[j]->sanity = S_ENCLOSED;
          monitors[j]->enemy = i;
        }

  /* After checking for enclosure, check for other lossage against earlier
     monitors.  We do enclosure first so that we make sure to pick the
     larger one.
   */
  for (i = 0; i < count; i++)
    for (j = 0; j < i; j++)
      {
        if (monitors[i]->sanity != S_SANE) continue; /* already marked */
        if (monitors[j]->sanity != S_SANE) continue;
        if (monitors[i]->screen != monitors[j]->screen) continue;

        if (monitors_overlap_p (monitors[i], monitors[j]))
          {
            monitors[i]->sanity = S_OVERLAP;
            monitors[i]->enemy = j;
          }
      }

  /* Finally, make sure all monitors have sane positions and sizes.
     Xinerama sometimes reports 1024x768 VPs at -1936862040, -1953705044.
   */
  for (i = 0; i < count; i++)
    {
      if (monitors[i]->sanity != S_SANE) continue; /* already marked */
      if (X1    <  0      || Y1    <  0 || 
          W1    <= 0      || H1    <= 0 || 
          X1+W1 >= 0x7FFF || Y1+H1 >= 0x7FFF)
        {
          monitors[i]->sanity = S_OFFSCREEN;
          monitors[i]->enemy = 0;
        }
    }

#  undef X1
#  undef X2
#  undef Y1
#  undef Y2
#  undef W1
#  undef W2
#  undef H1
#  undef H2
}


Bool
monitor_layouts_differ_p (monitor **a, monitor **b)
{
  if (!a || !b) return True;
  while (1)
    {
      if (!*a) break;
      if (!*b) break;
      if ((*a)->screen != (*b)->screen ||
          (*a)->x      != (*b)->x      ||
          (*a)->y      != (*b)->y      ||
          (*a)->width  != (*b)->width  ||
          (*a)->height != (*b)->height)
        return True;
      a++;
      b++;
    }
  if (*a) return True;
  if (*b) return True;

  return False;
}


static int
screen_number (Screen *screen)
{
  Display *dpy = DisplayOfScreen (screen);
  int i;
  for (i = 0; i < ScreenCount (dpy); i++)
    if (ScreenOfDisplay (dpy, i) == screen)
      return i;
  return 0;
}


void
describe_monitor_layout (monitor **monitors)
{
  int count = 0;
  int good_count = 0;
  int bad_count = 0;
  int implausible_p = !plausible_aspect_ratio_p (monitors);

  while (monitors[count])
    {
      if (monitors[count]->sanity == S_SANE)
        good_count++;
      else
        bad_count++;
      count++;
    }

  if (monitors && *monitors && monitors[0]->err)   /* deferred error msg */
    {
      char *token = strtok (monitors[0]->err, "\n");
      while (token)
        {
          fprintf (stderr, "%s: %s\n", blurb(), token);
          token = strtok (0, "\n");
        }
      free (monitors[0]->err);
      monitors[0]->err = 0;
    }

  if (count == 0)
    fprintf (stderr, "%s: no screens!\n", blurb());
  else
    {
      int i;
      fprintf (stderr, "%s: screens in use: %d\n", blurb(), good_count);
      for (i = 0; i < count; i++)
        {
          monitor *m = monitors[i];
          if (m->sanity != S_SANE) continue;
          fprintf (stderr, "%s:  %3d/%d: %dx%d+%d+%d",
                   blurb(), m->id, screen_number (m->screen),
                   m->width, m->height, m->x, m->y);
          if (m->desc && *m->desc) fprintf (stderr, " (%s)", m->desc);
          fprintf (stderr, "\n");
        }
      if (bad_count > 0)
        {
          fprintf (stderr, "%s: rejected screens: %d\n", blurb(), bad_count);
          for (i = 0; i < count; i++)
            {
              monitor *m = monitors[i];
              monitor *e = monitors[m->enemy];
              if (m->sanity == S_SANE) continue;
              fprintf (stderr, "%s:  %3d/%d: %dx%d+%d+%d",
                       blurb(), m->id, screen_number (m->screen),
                       m->width, m->height, m->x, m->y);
              if (m->desc && *m->desc) fprintf (stderr, " (%s)", m->desc);
              fprintf (stderr, " -- ");
              switch (m->sanity)
                {
                case S_SANE: abort(); break;
                case S_ENCLOSED:
                  fprintf (stderr, "enclosed by %d (%dx%d+%d+%d)\n",
                           e->id, e->width, e->height, e->x, e->y);
                  break;
                case S_DUPLICATE:
                  fprintf (stderr, "duplicate of %d\n", e->id);
                  break;
                case S_OVERLAP:
                  fprintf (stderr, "overlaps %d (%dx%d+%d+%d)\n",
                           e->id, e->width, e->height, e->x, e->y);
                  break;
                case S_OFFSCREEN:
                  fprintf (stderr, "off screen (%dx%d)\n",
                           WidthOfScreen (e->screen), 
                           HeightOfScreen (e->screen));
                  break;
                case S_DISABLED:
                  fprintf (stderr, "output disabled\n");
                  break;
                }
            }
        }

      if (implausible_p)
        fprintf (stderr,
                 "%s: WARNING: single screen aspect ratio is %dx%d = %.2f\n"
                 "%s:          probable X server bug in Xinerama/RANDR!\n",
                 blurb(), monitors[0]->width, monitors[0]->height,
                 monitors[0]->width / (double) monitors[0]->height,
                 blurb());
    }
}