path: root/driver/xscreensaver-getimage.c

/* xscreensaver, Copyright (c) 2001-2018 by 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.
 */

/* xscreensaver-getimage -- helper program that puts a random image
   onto the given window or pixmap.  That image is either a screen-grab,
   a file loaded from disk, or a frame grabbed from the system's video
   input.
 */

#include "utils.h"

#include <X11/Intrinsic.h>
#include <ctype.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/time.h>

#ifdef HAVE_SYS_WAIT_H
# include <sys/wait.h>		/* for waitpid() and associated macros */
#endif

#ifdef HAVE_XMU
# ifndef VMS
#  include <X11/Xmu/Error.h>
# else /* VMS */
#  include <Xmu/Error.h>
# endif
#else
# include "xmu.h"
#endif

#include "yarandom.h"
#include "grabscreen.h"
#include "resources.h"
#include "colorbars.h"
#include "visual.h"
#include "prefs.h"
#include "version.h"
#include "vroot.h"

#ifndef _XSCREENSAVER_VROOT_H_
# error Error!  You have an old version of vroot.h!  Check -I args.
#endif /* _XSCREENSAVER_VROOT_H_ */

#ifdef HAVE_GDK_PIXBUF
# undef HAVE_JPEGLIB
# ifdef HAVE_GTK2
#  include <gdk-pixbuf-xlib/gdk-pixbuf-xlib.h>
# else  /* !HAVE_GTK2 */
#  include <gdk-pixbuf/gdk-pixbuf-xlib.h>
# endif /* !HAVE_GTK2 */
#endif /* HAVE_GDK_PIXBUF */

#ifdef HAVE_JPEGLIB
# undef HAVE_GDK_PIXBUF
# include <jpeglib.h>
#endif


#ifdef __APPLE__
  /* On MacOS under X11, the usual X11 mechanism of getting a screen shot
     doesn't work, and we need to use an external program.  This is only
     used when running under X11 on MacOS.  If it's a Cocoa build, this
     path is not taken, and OSX/grabclient-osx.m is used instead.
   */
# define USE_EXTERNAL_SCREEN_GRABBER
#endif


#ifdef __GNUC__
 __extension__     /* shut up about "string length is greater than the length
                      ISO C89 compilers are required to support" when including
                      the .ad file... */
#endif

static char *defaults[] = {
#include "../driver/XScreenSaver_ad.h"
 0
};



char *progname = 0;
char *progclass = "XScreenSaver";
XrmDatabase db;
XtAppContext app;

extern void grabscreen_verbose (void);

typedef enum {
  GRAB_DESK, GRAB_VIDEO, GRAB_FILE, GRAB_BARS
} grab_type;


#define GETIMAGE_VIDEO_PROGRAM   "xscreensaver-getimage-video"
#define GETIMAGE_FILE_PROGRAM    "xscreensaver-getimage-file"
#define GETIMAGE_SCREEN_PROGRAM  "xscreensaver-getimage-desktop"

extern const char *blurb (void);

const char *
blurb (void)
{
  return progname;
}


static int
x_ehandler (Display *dpy, XErrorEvent *error)
{
  if (error->error_code == BadWindow || error->error_code == BadDrawable)
    {
      fprintf (stderr, "%s: target %s 0x%lx unexpectedly deleted\n", progname,
               (error->error_code == BadWindow ? "window" : "pixmap"),
               (unsigned long) error->resourceid);
    }
  else
    {
      fprintf (stderr, "\nX error in %s:\n", progname);
      XmuPrintDefaultErrorMessage (dpy, error, stderr);
    }
  exit (-1);
  return 0;
}


static Bool error_handler_hit_p = False;

static int
ignore_all_errors_ehandler (Display *dpy, XErrorEvent *error)
{
  error_handler_hit_p = True;
  return 0;
}

#ifndef USE_EXTERNAL_SCREEN_GRABBER
static int
ignore_badmatch_ehandler (Display *dpy, XErrorEvent *error)
{
  if (error->error_code == BadMatch)
    return ignore_all_errors_ehandler (dpy, error);
  else
    return x_ehandler (dpy, error);
}
#endif /* ! USE_EXTERNAL_SCREEN_GRABBER */


/* Returns True if the given Drawable is a Window; False if it's a Pixmap.
 */
static Bool
drawable_window_p (Display *dpy, Drawable d)
{
  XErrorHandler old_handler;
  XWindowAttributes xgwa;

  XSync (dpy, False);
  old_handler = XSetErrorHandler (ignore_all_errors_ehandler);
  error_handler_hit_p = False;
  XGetWindowAttributes (dpy, d, &xgwa);
  XSync (dpy, False);
  XSetErrorHandler (old_handler);
  XSync (dpy, False);

  if (!error_handler_hit_p)
    return True;   /* It's a Window. */
  else
    return False;  /* It's a Pixmap, or an invalid ID. */
}


/* Returns true if the window is the root window, or a virtual root window,
   but *not* the xscreensaver window.  That is, if it's a "real" desktop
   root window of some kind.
 */
static Bool
root_window_p (Screen *screen, Window window)
{
  Display *dpy = DisplayOfScreen (screen);
  Atom type;
  int format;
  unsigned long nitems, bytesafter;
  unsigned char *version;

  if (window != RootWindowOfScreen (screen))
    return False;

  if (XGetWindowProperty (dpy, window,
			  XInternAtom (dpy, "_SCREENSAVER_VERSION", False),
			  0, 1, False, XA_STRING,
			  &type, &format, &nitems, &bytesafter,
			  &version)
      == Success
      && type != None)
    return False;

  return True;
}


/* Clear the window or pixmap to black, or its background color.
 */
static void
clear_drawable (Screen *screen, Drawable drawable)
{
  Display *dpy = DisplayOfScreen (screen);
  XGCValues gcv;
  GC gc;
  Window root;
  int x, y;
  unsigned int w, h, bw, d;
  XGetGeometry (dpy, drawable, &root, &x, &y, &w, &h, &bw, &d);

  /* The window might have no-op background of None, so to clear it,
     draw a black rectangle first, then do XClearWindow (in case the
     actual background color is non-black...) */

  /* #### really we should allocate "black" instead, but I'm lazy... */
  gcv.foreground = BlackPixelOfScreen (screen);
  gc = XCreateGC (dpy, drawable, GCForeground, &gcv);
  XFillRectangle (dpy, drawable, gc, 0, 0, w, h);
  XFreeGC (dpy, gc);
  if (drawable_window_p (dpy, drawable))
    XClearWindow (dpy, (Window) drawable);
  XFlush (dpy);
}


/* Figure out what kind of scaling/positioning we ought to do to display
   a src-sized image in a dest-sized window/pixmap.  Returns the width
   and height to which the image should be scaled, and the position where
   it should be displayed to center it.
 */
static void
compute_image_scaling (int src_w, int src_h,
                       int dest_w, int dest_h,
                       Bool verbose_p,
                       int *scaled_from_x_ret, int *scaled_from_y_ret,
                       int *scaled_to_x_ret, int *scaled_to_y_ret,
                       int *scaled_w_ret, int *scaled_h_ret)
{
  int srcx, srcy, destx, desty;

  Bool exact_fit_p = ((src_w == dest_w && src_h <= dest_h) ||
                      (src_h == dest_h && src_w <= dest_w));

  if (!exact_fit_p)  /* scale the image up or down */
    {
      float rw = (float) dest_w  / src_w;
      float rh = (float) dest_h / src_h;
      float r = (rw < rh ? rw : rh);
      int tw, th, pct;

      /* If the window is a goofy aspect ratio, take a middle slice of
         the image instead. */
      if (dest_w > dest_h * 5 || dest_h > dest_w * 5)
        {
          double r2 = (dest_w > dest_h
                       ? dest_w / (double) dest_h
                       : dest_h / (double) dest_w);
          r *= r2;
          if (verbose_p)
            fprintf (stderr, "%s: weird aspect: scaling by %.1f\n",
                     progname, r2);
        }

      tw = src_w * r;
      th = src_h * r;
      pct = (r * 100);

#if 0
      /* this optimization breaks things */
      if (pct < 95 || pct > 105)  /* don't scale if it's close */
#endif
        {
          if (verbose_p)
            fprintf (stderr, "%s: scaling image by %d%% (%dx%d -> %dx%d)\n",
                     progname, pct, src_w, src_h, tw, th);
          src_w = tw;
          src_h = th;
        }
    }

  /* Center the image on the window/pixmap. */
  srcx = 0;
  srcy = 0;
  destx = (dest_w - src_w) / 2;
  desty = (dest_h - src_h) / 2;
  if (destx < 0) srcx = -destx, destx = 0;
  if (desty < 0) srcy = -desty, desty = 0;

  /* if (dest_w < src_w) src_w = dest_w;
     if (dest_h < src_h) src_h = dest_h; */

  *scaled_w_ret = src_w;
  *scaled_h_ret = src_h;
  *scaled_from_x_ret = srcx;
  *scaled_from_y_ret = srcy;
  *scaled_to_x_ret = destx;
  *scaled_to_y_ret = desty;

  if (verbose_p)
    fprintf (stderr, "%s: displaying %dx%d+%d+%d image at %d,%d in %dx%d.\n",
             progname, src_w, src_h, srcx, srcy, destx, desty, dest_w, dest_h);
}


static void
colorbars (Screen *screen, Visual *visual, Drawable drawable, Colormap cmap)
{
  Pixmap mask = 0;
  unsigned long *pixels; /* ignored - unfreed */
  int npixels;
  Pixmap logo = xscreensaver_logo (screen, visual, drawable, cmap,
                                   BlackPixelOfScreen (screen),
                                   &pixels, &npixels, &mask, True);
  draw_colorbars (screen, visual, drawable, cmap, 0, 0, 0, 0, logo, mask);
  XFreePixmap (DisplayOfScreen (screen), logo);
  XFreePixmap (DisplayOfScreen (screen), mask);
}


/* Scales an XImage, modifying it in place.
   This doesn't do dithering or smoothing, so it might have artifacts.
   If out of memory, returns False, and the XImage will have been
   destroyed and freed.
 */
#if !defined(USE_EXTERNAL_SCREEN_GRABBER) || defined(HAVE_JPEGLIB)
static Bool
scale_ximage (Screen *screen, Visual *visual,
              XImage *ximage, int new_width, int new_height)
{
  Display *dpy = DisplayOfScreen (screen);
  int depth = visual_depth (screen, visual);
  int x, y;
  double xscale, yscale;

  XImage *ximage2 = XCreateImage (dpy, visual, depth,
                                  ZPixmap, 0, 0,
                                  new_width, new_height, 8, 0);
  ximage2->data = (char *) calloc (ximage2->height, ximage2->bytes_per_line);

  if (!ximage2->data)
    {
      fprintf (stderr, "%s: out of memory scaling %dx%d image to %dx%d\n",
               progname,
               ximage->width, ximage->height,
               ximage2->width, ximage2->height);
      if (ximage->data) free (ximage->data);
      if (ximage2->data) free (ximage2->data);
      ximage->data = 0;
      ximage2->data = 0;
      XDestroyImage (ximage);
      XDestroyImage (ximage2);
      return False;
    }

  /* Brute force scaling... */
  xscale = (double) ximage->width  / ximage2->width;
  yscale = (double) ximage->height / ximage2->height;
  for (y = 0; y < ximage2->height; y++)
    for (x = 0; x < ximage2->width; x++)
      XPutPixel (ximage2, x, y,
                 XGetPixel (ximage, x * xscale, y * yscale));

  free (ximage->data);
  ximage->data = 0;

  (*ximage) = (*ximage2);

  ximage2->data = 0;
  XDestroyImage (ximage2);

  return True;
}
#endif /* !USE_EXTERNAL_SCREEN_GRABBER || HAVE_JPEGLIB */


#ifdef HAVE_GDK_PIXBUF

/* Reads the given image file and renders it on the Drawable, using GDK.
   Returns False if it fails.
 */
static Bool
read_file_gdk (Screen *screen, Window window, Drawable drawable,
               const char *filename, Bool verbose_p,
               XRectangle *geom_ret)
{
  GdkPixbuf *pb;
  Display *dpy = DisplayOfScreen (screen);
  unsigned int win_width, win_height, win_depth;
# ifdef HAVE_GTK2
  GError *gerr = 0;
# endif /* HAVE_GTK2 */

  /* Find the size of the Drawable. */
  {
    Window root;
    int x, y;
    unsigned int bw;
    XGetGeometry (dpy, drawable,
                  &root, &x, &y, &win_width, &win_height, &bw, &win_depth);
  }

  gdk_pixbuf_xlib_init_with_depth (dpy, screen_number (screen), win_depth);
# ifdef HAVE_GTK2
# if !GLIB_CHECK_VERSION(2, 36 ,0)
  g_type_init();
# endif
# else  /* !HAVE_GTK2 */
  xlib_rgb_init (dpy, screen);
# endif /* !HAVE_GTK2 */

  pb = gdk_pixbuf_new_from_file (filename
# ifdef HAVE_GTK2
                                 , &gerr
# endif /* HAVE_GTK2 */
                                 );

  if (!pb)
    {
      fprintf (stderr, "%s: unable to load \"%s\"\n", progname, filename);
#  ifdef HAVE_GTK2
      if (gerr && gerr->message && *gerr->message)
        fprintf (stderr, "%s: reason: %s\n", progname, gerr->message);
#  endif /* HAVE_GTK2 */
      return False;
    }
  else
    {
      int w = gdk_pixbuf_get_width (pb);
      int h = gdk_pixbuf_get_height (pb);
      int srcx, srcy, destx, desty, w2, h2;
      Bool bg_p = False;

# ifdef HAVE_GDK_PIXBUF_APPLY_EMBEDDED_ORIENTATION
      {
        int ow = w, oh = h;
        GdkPixbuf *opb = pb;
        pb = gdk_pixbuf_apply_embedded_orientation (opb);
        g_object_unref (opb);
        w = gdk_pixbuf_get_width (pb);
        h = gdk_pixbuf_get_height (pb);
        if (verbose_p && (w != ow || h != oh))
          fprintf (stderr, "%s: rotated %dx%d to %dx%d\n",
                   progname, ow, oh, w, h);
      }
# endif

      compute_image_scaling (w, h, win_width, win_height, verbose_p,
                             &srcx, &srcy, &destx, &desty, &w2, &h2);
      if (w != w2 || h != h2)
        {
          GdkPixbuf *pb2 = gdk_pixbuf_scale_simple (pb, w2, h2,
                                                    GDK_INTERP_BILINEAR);
          if (pb2)
            {
              g_object_unref (pb);
              pb = pb2;
              w = w2;
              h = h2;
            }
          else
            fprintf (stderr, "%s: out of memory when scaling?\n", progname);
        }

      /* If we're rendering onto the root window (and it's not the
         xscreensaver pseudo-root) then put the image in the window's
         background.  Otherwise, just paint the image onto the window.
       */
      bg_p = (window == drawable && root_window_p (screen, window));

      if (bg_p)
        {
          XGCValues gcv;
          GC gc;
          drawable = XCreatePixmap (dpy, window,
                                    win_width, win_height, win_depth);
          gcv.foreground = BlackPixelOfScreen (screen);
          gc = XCreateGC (dpy, drawable, GCForeground, &gcv);
          XFillRectangle (dpy, drawable, gc, 0, 0, win_width, win_height);
          XFreeGC (dpy, gc);
        }
      else
        clear_drawable (screen, drawable);

      /* #### Note that this always uses the default colormap!  Morons!
         Owen says that in Gnome 2.0, I should try using
         gdk_pixbuf_render_pixmap_and_mask_for_colormap() instead.
         But I haven't tried.
       */
      if (srcx > 0) w -= srcx;
      if (srcy > 0) h -= srcy;
      gdk_pixbuf_xlib_render_to_drawable_alpha (pb, drawable,
                                                srcx, srcy, destx, desty,
                                                w, h,
                                                GDK_PIXBUF_ALPHA_FULL, 127,
                                                XLIB_RGB_DITHER_NORMAL,
                                                0, 0);
      if (bg_p)
        {
          XSetWindowBackgroundPixmap (dpy, window, drawable);
          XClearWindow (dpy, window);
        }

      if (geom_ret)
        {
          geom_ret->x = destx;
          geom_ret->y = desty;
          geom_ret->width  = w;
          geom_ret->height = h;
        }
    }

  XSync (dpy, False);
  return True;
}

#endif /* HAVE_GDK_PIXBUF */



#ifdef HAVE_JPEGLIB

/* Allocates a colormap that makes a PseudoColor or DirectColor
   visual behave like a TrueColor visual of the same depth.

   #### Duplicated in utils/grabscreen.c
 */
static void
allocate_cubic_colormap (Screen *screen, Visual *visual, Colormap cmap,
                         Bool verbose_p)
{
  Display *dpy = DisplayOfScreen (screen);
  int nr, ng, nb, cells;
  int r, g, b;
  int depth;
  XColor colors[4097];
  int i;

  depth = visual_depth (screen, visual);

  switch (depth)
    {
    case 8:  nr = 3; ng = 3; nb = 2; cells = 256;  break;
    case 12: nr = 4; ng = 4; nb = 4; cells = 4096; break;
    default: abort(); break;
    }

  memset(colors, 0, sizeof(colors));
  for (r = 0; r < (1 << nr); r++)
    for (g = 0; g < (1 << ng); g++)
      for (b = 0; b < (1 << nb); b++)
	{
	  i = (r | (g << nr) | (b << (nr + ng)));
	  colors[i].pixel = i;
          colors[i].flags = DoRed|DoGreen|DoBlue;
	  if (depth == 8)
	    {
	      colors[i].red   = ((r << 13) | (r << 10) | (r << 7) |
				 (r <<  4) | (r <<  1));
	      colors[i].green = ((g << 13) | (g << 10) | (g << 7) |
				 (g <<  4) | (g <<  1));
	      colors[i].blue  = ((b << 14) | (b << 12) | (b << 10) |
				 (b <<  8) | (b <<  6) | (b <<  4) |
				 (b <<  2) | b);
	    }
	  else
	    {
	      colors[i].red   = (r << 12) | (r << 8) | (r << 4) | r;
	      colors[i].green = (g << 12) | (g << 8) | (g << 4) | g;
	      colors[i].blue  = (b << 12) | (b << 8) | (b << 4) | b;
	    }
	}

  {
    int j;
    int allocated = 0;
    int interleave = cells / 8;  /* skip around, rather than allocating in
                                    order, so that we get better coverage if
                                    we can't allocated all of them. */
    for (j = 0; j < interleave; j++)
      for (i = 0; i < cells; i += interleave)
        if (XAllocColor (dpy, cmap, &colors[i + j]))
          allocated++;

    if (verbose_p)
      fprintf (stderr, "%s: allocated %d of %d colors for cubic map\n",
               progname, allocated, cells);
  }
}

/* Find the pixel index that is closest to the given color
   (using linear distance in RGB space -- which is far from the best way.)

   #### Duplicated in utils/grabscreen.c
 */
static unsigned long
find_closest_pixel (XColor *colors, int ncolors,
                    unsigned long r, unsigned long g, unsigned long b)
{
  unsigned long distance = ~0;
  int i, found = 0;

  if (ncolors == 0)
    abort();
  for (i = 0; i < ncolors; i++)
    {
      unsigned long d;
      int rd, gd, bd;

      rd = r - colors[i].red;
      gd = g - colors[i].green;
      bd = b - colors[i].blue;
      if (rd < 0) rd = -rd;
      if (gd < 0) gd = -gd;
      if (bd < 0) bd = -bd;
      d = (rd << 1) + (gd << 2) + bd;
      
      if (d < distance)
	{
	  distance = d;
	  found = i;
          if (distance == 0)
              break;
	}
    }

  return found;
}


/* Given an XImage with 8-bit or 12-bit RGB data, convert it to be 
   displayable with the given X colormap.  The farther from a perfect
   color cube the contents of the colormap are, the lossier the 
   transformation will be.  No dithering is done.

   #### Duplicated in utils/grabscreen.c
 */
static void
remap_image (Screen *screen, Colormap cmap, XImage *image, Bool verbose_p)
{
  Display *dpy = DisplayOfScreen (screen);
  unsigned long map[4097];
  int x, y, i;
  int cells;
  XColor colors[4097];

  if (image->depth == 8)
    cells = 256;
  else if (image->depth == 12)
    cells = 4096;
  else
    abort();

  memset(map,    -1, sizeof(*map));
  memset(colors, -1, sizeof(*colors));

  for (i = 0; i < cells; i++)
    colors[i].pixel = i;
  XQueryColors (dpy, cmap, colors, cells);

  if (verbose_p)
    fprintf(stderr, "%s: building color cube for %d bit image\n",
            progname, image->depth);

  for (i = 0; i < cells; i++)
    {
      unsigned short r, g, b;

      if (cells == 256)
        {
          /* "RRR GGG BB" In an 8 bit map.  Convert that to
             "RRR RRR RR" "GGG GGG GG" "BB BB BB BB" to give
             an even spread. */
          r = (i & 0x07);
          g = (i & 0x38) >> 3;
          b = (i & 0xC0) >> 6;

          r = ((r << 13) | (r << 10) | (r << 7) | (r <<  4) | (r <<  1));
          g = ((g << 13) | (g << 10) | (g << 7) | (g <<  4) | (g <<  1));
          b = ((b << 14) | (b << 12) | (b << 10) | (b <<  8) |
               (b <<  6) | (b <<  4) | (b <<  2) | b);
        }
      else
        {
          /* "RRRR GGGG BBBB" In a 12 bit map.  Convert that to
             "RRRR RRRR" "GGGG GGGG" "BBBB BBBB" to give an even
             spread. */
          r = (i & 0x00F);
          g = (i & 0x0F0) >> 4;
          b = (i & 0xF00) >> 8;

          r = (r << 12) | (r << 8) | (r << 4) | r;
          g = (g << 12) | (g << 8) | (g << 4) | g;
          b = (b << 12) | (b << 8) | (b << 4) | b;
        }

      map[i] = find_closest_pixel (colors, cells, r, g, b);
    }

  if (verbose_p)
    fprintf(stderr, "%s: remapping colors in %d bit image\n",
            progname, image->depth);

  for (y = 0; y < image->height; y++)
    for (x = 0; x < image->width; x++)
      {
        unsigned long pixel = XGetPixel(image, x, y);
        if (pixel >= cells) abort();
        XPutPixel(image, x, y, map[pixel]);
      }
}


/* If the file has a PPM (P6) on it, read it and return an XImage.
   Otherwise, rewind the fd back to the beginning, and return 0.
 */
static XImage *
maybe_read_ppm (Screen *screen, Visual *visual,
                const char *filename, FILE *in, Bool verbose_p)
{
  Display *dpy = DisplayOfScreen (screen);
  int depth = visual_depth (screen, visual);
  struct stat st;
  char *buf = 0;
  int bufsiz = 0;
  char *s, dummy;
  int i, j;
  int x, y, w, h, maxval;
  XImage *ximage = 0;

  if (fstat (fileno (in), &st))
    goto FAIL;

  bufsiz = st.st_size;
  buf = (char *) malloc (bufsiz + 1);
  if (!buf)
    {
      fprintf (stderr, "%s: out of memory loading %d byte PPM file %s\n",
               progname, bufsiz, filename);
      goto FAIL;
    }

  if (! (s = fgets (buf, bufsiz, in)))   /* line 1 */
    goto FAIL;

  if (!strncmp (buf, "\107\111", 2))
    {
      fprintf (stderr, "%s: %s: sorry, GIF files not supported"
               " when compiled with JPEGlib instead of GDK_Pixbuf.\n",
               progname, filename);
      goto FAIL;
    }
  else if (!strncmp (buf, "\211\120", 2))
    {
      fprintf (stderr, "%s: %s: sorry, PNG files not supported"
               " when compiled with JPEGlib instead of GDK_Pixbuf.\n",
               progname, filename);
      goto FAIL;
    }

  if (strncmp (s, "P6", 2))
    goto FAIL;

  if (! (s = fgets (buf, bufsiz, in)))   /* line 2 */
    goto FAIL;
  if (2 != sscanf (s, " %d %d %c", &w, &h, &dummy))
    {
      fprintf (stderr, "%s: %s: invalid PPM (line 2)\n", progname, filename);
      goto FAIL;
    }

  if (! (s = fgets (buf, bufsiz, in)))   /* line 3 */
    goto FAIL;
  if (1 != sscanf (s, " %d %c", &maxval, &dummy))
    {
      fprintf (stderr, "%s: %s: invalid PPM (line 3)\n", progname, filename);
      goto FAIL;
    }
  if (maxval != 255)
    {
      fprintf (stderr, "%s: %s: unparsable PPM: maxval is %d\n",
               progname, filename, maxval);
      goto FAIL;
    }

  ximage = XCreateImage (dpy, visual, depth, ZPixmap, 0, 0,
                         w, h, 8, 0);
  if (ximage)
    ximage->data = (char *) calloc (ximage->height, ximage->bytes_per_line);
  if (!ximage || !ximage->data)
    {
      fprintf (stderr, "%s: out of memory loading %dx%d PPM file %s\n",
               progname, ximage->width, ximage->height, filename);
      goto FAIL;
    }

  s = buf;
  j = bufsiz;
  while ((i = fread (s, 1, j, in)) > 0)
    s += i, j -= i;

  i = 0;
  for (y = 0; y < ximage->height; y++)
    for (x = 0; x < ximage->width; x++)
      {
        unsigned char r = buf[i++];
        unsigned char g = buf[i++];
        unsigned char b = buf[i++];
        unsigned long pixel;

        if (depth > 16)
          pixel = (r << 16) | (g << 8) | b;
        else if (depth == 8)
          pixel = ((r >> 5) | ((g >> 5) << 3) | ((b >> 6) << 6));
        else if (depth == 12)
          pixel = ((r >> 4) | ((g >> 4) << 4) | ((b >> 4) << 8));
        else if (depth == 16 || depth == 15)
          pixel = (((r >> 3) << 10) | ((g >> 3) << 5) | ((b >> 3)));
        else
          abort();

        XPutPixel (ximage, x, y, pixel);
      }

  free (buf);
  return ximage;

 FAIL:
  if (buf) free (buf);
  if (ximage && ximage->data)
    {
      free (ximage->data);
      ximage->data = 0;
    }
  if (ximage) XDestroyImage (ximage);
  fseek (in, 0, SEEK_SET);
  return 0;
}


typedef struct {
  struct jpeg_error_mgr pub;   /* this is what passes for subclassing in C */
  const char *filename;
  Screen *screen;
  Visual *visual;
  Drawable drawable;
  Colormap cmap;
} getimg_jpg_error_mgr;


static void
jpg_output_message (j_common_ptr cinfo)
{
  getimg_jpg_error_mgr *err = (getimg_jpg_error_mgr *) cinfo->err;
  char buf[JMSG_LENGTH_MAX];
  cinfo->err->format_message (cinfo, buf);
  fprintf (stderr, "%s: %s: %s\n", progname, err->filename, buf);
}


static void
jpg_error_exit (j_common_ptr cinfo)
{
  getimg_jpg_error_mgr *err = (getimg_jpg_error_mgr *) cinfo->err;
  cinfo->err->output_message (cinfo);
  colorbars (err->screen, err->visual, err->drawable, err->cmap);
  XSync (DisplayOfScreen (err->screen), False);
  exit (1);
}


/* Reads a JPEG file, returns an RGB XImage of it.
 */
static XImage *
read_jpeg_ximage (Screen *screen, Visual *visual, Drawable drawable,
                  Colormap cmap, const char *filename, Bool verbose_p)
{
  Display *dpy = DisplayOfScreen (screen);
  int depth = visual_depth (screen, visual);

  FILE *in = 0;
  XImage *ximage = 0;
  struct jpeg_decompress_struct cinfo;
  getimg_jpg_error_mgr jerr;
  JSAMPARRAY scanbuf = 0;
  int y;

  jerr.filename = filename;
  jerr.screen = screen;
  jerr.visual = visual;
  jerr.drawable = drawable;
  jerr.cmap = cmap;

  if (! (depth >= 15 || depth == 12 || depth == 8))
    {
      fprintf (stderr, "%s: unsupported depth: %d\n", progname, depth);
      goto FAIL;
    }

  in = fopen (filename, "rb");
  if (!in)
    {
      fprintf (stderr, "%s: %s: unreadable\n", progname, filename);
      goto FAIL;
    }

  /* Check to see if it's a PPM, and if so, read that instead of using
     the JPEG library.  Yeah, this is all modular and stuff.
   */
  if ((ximage = maybe_read_ppm (screen, visual, filename, in, verbose_p)))
    {
      fclose (in);
      return ximage;
    }

  cinfo.err = jpeg_std_error (&jerr.pub);
  jerr.pub.output_message = jpg_output_message;
  jerr.pub.error_exit = jpg_error_exit;

  jpeg_create_decompress (&cinfo);
  jpeg_stdio_src (&cinfo, in);
  jpeg_read_header (&cinfo, TRUE);

  /* set some decode parameters */
  cinfo.out_color_space = JCS_RGB;
  cinfo.quantize_colors = FALSE;

  jpeg_start_decompress (&cinfo);

  ximage = XCreateImage (dpy, visual, depth, ZPixmap, 0, 0,
                         cinfo.output_width, cinfo.output_height,
                         8, 0);
  if (ximage)
    ximage->data = (char *) calloc (ximage->height, ximage->bytes_per_line);

  if (ximage && ximage->data)
    scanbuf = (*cinfo.mem->alloc_sarray) ((j_common_ptr) &cinfo, JPOOL_IMAGE,
                                          cinfo.rec_outbuf_height *
                                          cinfo.output_width *
                                          cinfo.output_components,
                                          1);
  if (!ximage || !ximage->data || !scanbuf)
    {
      fprintf (stderr, "%s: out of memory loading %dx%d file %s\n",
               progname, ximage->width, ximage->height, filename);
      goto FAIL;
    }

  y = 0;
  while (cinfo.output_scanline < cinfo.output_height)
    {
      int n = jpeg_read_scanlines (&cinfo, scanbuf, 1);
      int i;
      for (i = 0; i < n; i++)
        {
          int x;
          for (x = 0; x < ximage->width; x++)
            {
              int j = x * cinfo.output_components;
              unsigned char r = scanbuf[i][j];
              unsigned char g = scanbuf[i][j+1];
              unsigned char b = scanbuf[i][j+2];
              unsigned long pixel;

              if (depth > 16)
                pixel = (r << 16) | (g << 8) | b;
              else if (depth == 8)
                pixel = ((r >> 5) | ((g >> 5) << 3) | ((b >> 6) << 6));
              else if (depth == 12)
                pixel = ((r >> 4) | ((g >> 4) << 4) | ((b >> 4) << 8));
              else if (depth == 15)
                /* Gah! I don't understand why these are in the other
                   order. */
                pixel = (((r >> 3) << 10) | ((g >> 3) << 5) | ((b >> 3)));
              else if (depth == 16)
                pixel = (((r >> 3) << 11) | ((g >> 2) << 5) | ((b >> 3)));
              else
                abort();

              XPutPixel (ximage, x, y, pixel);
            }
          y++;
        }
    }

  if (cinfo.output_scanline < cinfo.output_height)
    /* don't goto FAIL -- we might have viewable partial data. */
    jpeg_abort_decompress (&cinfo);
  else
    jpeg_finish_decompress (&cinfo);

  jpeg_destroy_decompress (&cinfo);
  fclose (in);
  in = 0;

  return ximage;

 FAIL:
  if (in) fclose (in);
  if (ximage && ximage->data)
    {
      free (ximage->data);
      ximage->data = 0;
    }
  if (ximage) XDestroyImage (ximage);
  if (scanbuf) free (scanbuf);
  return 0;
}


/* Reads the given image file and renders it on the Drawable, using JPEG lib.
   Returns False if it fails.
 */
static Bool
read_file_jpeglib (Screen *screen, Window window, Drawable drawable,
                   const char *filename, Bool verbose_p,
                   XRectangle *geom_ret)
{
  Display *dpy = DisplayOfScreen (screen);
  XImage *ximage;
  Visual *visual;
  int class, depth;
  Colormap cmap;
  unsigned int win_width, win_height, win_depth;
  int srcx, srcy, destx, desty, w2, h2;

  /* Find the size of the Drawable, and the Visual/Colormap of the Window. */
  {
    Window root;
    int x, y;
    unsigned int bw;
    XWindowAttributes xgwa;
    XGetWindowAttributes (dpy, window, &xgwa);
    visual = xgwa.visual;
    cmap = xgwa.colormap;
    XGetGeometry (dpy, drawable,
                  &root, &x, &y, &win_width, &win_height, &bw, &win_depth);
  }

  /* Make sure we're not on some weirdo visual...
   */
  class = visual_class (screen, visual);
  depth = visual_depth (screen, visual);
  if ((class == PseudoColor || class == DirectColor) &&
      (depth != 8 && depth != 12))
    {
      fprintf (stderr, "%s: Pseudo/DirectColor depth %d unsupported\n",
               progname, depth);
      return False;
    }

  /* Read the file...
   */
  ximage = read_jpeg_ximage (screen, visual, drawable, cmap,
                             filename, verbose_p);
  if (!ximage) return False;

  /* Scale it, if necessary...
   */
  compute_image_scaling (ximage->width, ximage->height,
                         win_width, win_height, verbose_p,
                         &srcx, &srcy, &destx, &desty, &w2, &h2);
  if (ximage->width != w2 || ximage->height != h2)
    if (! scale_ximage (screen, visual, ximage, w2, h2))
      return False;

  /* Allocate a colormap, if we need to...
   */
  if (class == PseudoColor || class == DirectColor)
    {
      allocate_cubic_colormap (screen, visual, cmap, verbose_p);
      remap_image (screen, cmap, ximage, verbose_p);
    }

  /* Finally, put the resized image on the window.
   */
  {
    GC gc;
    XGCValues gcv;

    /* If we're rendering onto the root window (and it's not the xscreensaver
       pseudo-root) then put the image in the window's background.  Otherwise,
       just paint the image onto the window.
     */
    if (window == drawable && root_window_p (screen, window))
      {
        Pixmap bg = XCreatePixmap (dpy, window,
                                   win_width, win_height, win_depth);
        gcv.foreground = BlackPixelOfScreen (screen);
        gc = XCreateGC (dpy, drawable, GCForeground, &gcv);
        XFillRectangle (dpy, bg, gc, 0, 0, win_width, win_height);
        XPutImage (dpy, bg, gc, ximage,
                   srcx, srcy, destx, desty, ximage->width, ximage->height);
        XSetWindowBackgroundPixmap (dpy, window, bg);
        XClearWindow (dpy, window);
      }
    else
      {
        gc = XCreateGC (dpy, drawable, 0, &gcv);
        clear_drawable (screen, drawable);
        XPutImage (dpy, drawable, gc, ximage,
                   srcx, srcy, destx, desty, ximage->width, ximage->height);
      }

    XFreeGC (dpy, gc);
  }

  if (geom_ret)
    {
      geom_ret->x = destx;
      geom_ret->y = desty;
      geom_ret->width  = ximage->width;
      geom_ret->height = ximage->height;
    }

  free (ximage->data);
  ximage->data = 0;
  XDestroyImage (ximage);
  XSync (dpy, False);
  return True;
}

#endif /* HAVE_JPEGLIB */


/* Reads the given image file and renders it on the Drawable.
   Returns False if it fails.
 */
static Bool
display_file (Screen *screen, Window window, Drawable drawable,
              const char *filename, Bool verbose_p,
              XRectangle *geom_ret)
{
  if (verbose_p)
    fprintf (stderr, "%s: loading \"%s\"\n", progname, filename);

# if defined(HAVE_GDK_PIXBUF)
  if (read_file_gdk (screen, window, drawable, filename, verbose_p, geom_ret))
    return True;
# elif defined(HAVE_JPEGLIB)
  if (read_file_jpeglib (screen, window, drawable, filename, verbose_p,
                         geom_ret))
    return True;
# else  /* !(HAVE_GDK_PIXBUF || HAVE_JPEGLIB) */
  /* shouldn't get here if we have no image-loading methods available. */
  abort();
# endif /* !(HAVE_GDK_PIXBUF || HAVE_JPEGLIB) */

  return False;
}


/* Invokes a sub-process and returns its output (presumably, a file to
   load.)  Free the string when done.  'grab_type' controls which program
   to run.  Returned pathname may be relative to 'directory', or absolute.
 */
static char *
get_filename_1 (Screen *screen, const char *directory, grab_type type,
                Bool verbose_p)
{
  Display *dpy = DisplayOfScreen (screen);
  pid_t forked;
  int fds [2];
  int in, out;
  char buf[10240];
  char *av[20];
  int ac = 0;

  switch (type)
    {
    case GRAB_FILE:
      av[ac++] = GETIMAGE_FILE_PROGRAM;
      if (verbose_p)
        av[ac++] = "--verbose";
      av[ac++] = "--name";
      av[ac++] = (char *) directory;
      break;

    case GRAB_VIDEO:
      av[ac++] = GETIMAGE_VIDEO_PROGRAM;
      if (verbose_p)
        av[ac++] = "--verbose";
      av[ac++] = "--name";
      break;

# ifdef USE_EXTERNAL_SCREEN_GRABBER
    case GRAB_DESK:
      av[ac++] = GETIMAGE_SCREEN_PROGRAM;
      if (verbose_p)
        av[ac++] = "--verbose";
      av[ac++] = "--name";
      break;
# endif

    default:
      abort();
    }
  av[ac] = 0;

  if (verbose_p)
    {
      int i;
      fprintf (stderr, "%s: executing:", progname);
      for (i = 0; i < ac; i++)
        fprintf (stderr, " %s", av[i]);
      fprintf (stderr, "\n");
    }

  if (pipe (fds))
    {
      sprintf (buf, "%s: error creating pipe", progname);
      perror (buf);
      return 0;
    }

  in = fds [0];
  out = fds [1];

  switch ((int) (forked = fork ()))
    {
    case -1:
      {
        sprintf (buf, "%s: couldn't fork", progname);
        perror (buf);
        return 0;
      }
    case 0:
      {
        int stdout_fd = 1;

        close (in);  /* don't need this one */
        close (ConnectionNumber (dpy));		/* close display fd */

        if (dup2 (out, stdout_fd) < 0)		/* pipe stdout */
          {
            sprintf (buf, "%s: could not dup() a new stdout", progname);
            exit (-1);                          /* exits fork */
          }

        execvp (av[0], av);			/* shouldn't return. */
        exit (-1);                              /* exits fork */
        break;
      }
    default:
      {
        struct stat st;
        int wait_status = 0;
        FILE *f = fdopen (in, "r");
        int L;
        char *ret = 0;

        close (out);  /* don't need this one */
        *buf = 0;
        if (! fgets (buf, sizeof(buf)-1, f))
          *buf = 0;
        fclose (f);

        /* Wait for the child to die. */
        waitpid (-1, &wait_status, 0);

        L = strlen (buf);
        while (L && buf[L-1] == '\n')
          buf[--L] = 0;
          
        if (!*buf)
          return 0;

        ret = strdup (buf);

        if (*ret != '/')
          {
            /* Program returned path relative to directory.  Prepend dir
               to buf so that we can properly stat it. */
            strcpy (buf, directory);
            if (directory[strlen(directory)-1] != '/')
              strcat (buf, "/");
            strcat (buf, ret);
          }

        if (stat(buf, &st))
          {
            fprintf (stderr, "%s: file does not exist: \"%s\"\n",
                     progname, buf);
            free (ret);
            return 0;
          }
        else
          return ret;
      }
    }

  abort();
}


/* Returns a pathname to an image file.  Free the string when you're done.
 */
static char *
get_filename (Screen *screen, const char *directory, Bool verbose_p)
{
  return get_filename_1 (screen, directory, GRAB_FILE, verbose_p);
}


/* Grabs a video frame to a file, and returns a pathname to that file.
   Delete that file when you are done with it (and free the string.)
 */
static char *
get_video_filename (Screen *screen, Bool verbose_p)
{
  return get_filename_1 (screen, 0, GRAB_VIDEO, verbose_p);
}

/* Grabs a desktop image to a file, and returns a pathname to that file.
   Delete that file when you are done with it (and free the string.)
 */
# ifdef USE_EXTERNAL_SCREEN_GRABBER
static char *
get_desktop_filename (Screen *screen, Bool verbose_p)
{
  return get_filename_1 (screen, 0, GRAB_DESK, verbose_p);
}
#endif /* USE_EXTERNAL_SCREEN_GRABBER */


/* Grabs a video frame, and renders it on the Drawable.
   Returns False if it fails;
 */
static Bool
display_video (Screen *screen, Window window, Drawable drawable,
               Bool verbose_p, XRectangle *geom_ret)
{
  char *filename = get_video_filename (screen, verbose_p);
  Bool status;

  if (!filename)
    {
      if (verbose_p)
        fprintf (stderr, "%s: video grab failed.\n", progname);
      return False;
    }

  status = display_file (screen, window, drawable, filename, verbose_p,
                         geom_ret);

  if (unlink (filename))
    {
      char buf[512];
      sprintf (buf, "%s: rm %.100s", progname, filename);
      perror (buf);
    }
  else if (verbose_p)
    fprintf (stderr, "%s: rm %s\n", progname, filename);

  if (filename) free (filename);
  return status;
}


/* Grabs a desktop screen shot onto the window and the drawable.
   If the window and drawable are not the same size, the image in
   the drawable is scaled to fit.
   Returns False if it fails.
 */
static Bool
display_desktop (Screen *screen, Window window, Drawable drawable,
                 Bool verbose_p, XRectangle *geom_ret)
{
# ifdef USE_EXTERNAL_SCREEN_GRABBER

  Display *dpy = DisplayOfScreen (screen);
  Bool top_p = top_level_window_p (screen, window);
  char *filename;
  Bool status;

  if (top_p)
    {
      if (verbose_p)
        fprintf (stderr, "%s: unmapping 0x%lx.\n", progname,
                 (unsigned long) window);
      XUnmapWindow (dpy, window);
      XSync (dpy, False);
    }

  filename = get_desktop_filename (screen, verbose_p);

  if (top_p)
    {
      if (verbose_p)
        fprintf (stderr, "%s: mapping 0x%lx.\n", progname,
                 (unsigned long) window);
      XMapRaised (dpy, window);
      XSync (dpy, False);
    }

  if (!filename)
    {
      if (verbose_p)
        fprintf (stderr, "%s: desktop grab failed.\n", progname);
      return False;
    }

  status = display_file (screen, window, drawable, filename, verbose_p,
                         geom_ret);

  if (unlink (filename))
    {
      char buf[512];
      sprintf (buf, "%s: rm %.100s", progname, filename);
      perror (buf);
    }
  else if (verbose_p)
    fprintf (stderr, "%s: rm %s\n", progname, filename);

  if (filename) free (filename);
  return status;

# else /* !USE_EXTERNAL_SCREEN_GRABBER */

  Display *dpy = DisplayOfScreen (screen);
  XGCValues gcv;
  XWindowAttributes xgwa;
  Window root;
  int px, py;
  unsigned int pw, ph, pbw, pd;
  int srcx, srcy, destx, desty, w2, h2;

  if (verbose_p)
    {
      fprintf (stderr, "%s: grabbing desktop image\n", progname);
      grabscreen_verbose();
    }

  XGetWindowAttributes (dpy, window, &xgwa);
  XGetGeometry (dpy, drawable, &root, &px, &py, &pw, &ph, &pbw, &pd);

  grab_screen_image_internal (screen, window);

  compute_image_scaling (xgwa.width, xgwa.height,
                         pw, ph, verbose_p,
                         &srcx, &srcy, &destx, &desty, &w2, &h2);

  if (pw == w2 && ph == h2)  /* it fits -- just copy server-side pixmaps */
    {
      GC gc = XCreateGC (dpy, drawable, 0, &gcv);
      XCopyArea (dpy, window, drawable, gc,
                 0, 0, xgwa.width, xgwa.height, 0, 0);
      XFreeGC (dpy, gc);
    }
  else  /* size mismatch -- must scale client-side images to fit drawable */
    {
      GC gc;
      XImage *ximage = 0;
      XErrorHandler old_handler;

      XSync (dpy, False);
      old_handler = XSetErrorHandler (ignore_badmatch_ehandler);
      error_handler_hit_p = False;

      /* This can return BadMatch if the window is not fully on screen.
         Trap that error and return color bars in that case.
         (Note that this only happens with XGetImage, not with XCopyArea:
         yet another totally gratuitous inconsistency in X, thanks.)
       */
      ximage = XGetImage (dpy, window, 0, 0, xgwa.width, xgwa.height,
                          ~0L, ZPixmap);

      XSync (dpy, False);
      XSetErrorHandler (old_handler);
      XSync (dpy, False);

      if (error_handler_hit_p)
        {
          ximage = 0;
          if (verbose_p)
            fprintf (stderr, "%s: BadMatch reading window 0x%x contents!\n",
                     progname, (unsigned int) window);
        }

      if (!ximage ||
          !scale_ximage (xgwa.screen, xgwa.visual, ximage, w2, h2))
        return False;

      gc = XCreateGC (dpy, drawable, 0, &gcv);
      clear_drawable (screen, drawable);
      XPutImage (dpy, drawable, gc, ximage, 
                 srcx, srcy, destx, desty, ximage->width, ximage->height);
      XDestroyImage (ximage);
      XFreeGC (dpy, gc);
    }

  if (geom_ret)
    {
      geom_ret->x = destx;
      geom_ret->y = desty;
      geom_ret->width  = w2;
      geom_ret->height = h2;
    }

  XSync (dpy, False);
  return True;

# endif /* !USE_EXTERNAL_SCREEN_GRABBER */
}


/* Whether the given Drawable is unreasonably small.
 */
static Bool
drawable_miniscule_p (Display *dpy, Drawable drawable)
{
  Window root;
  int xx, yy;
  unsigned int bw, d, w = 0, h = 0;
  XGetGeometry (dpy, drawable, &root, &xx, &yy, &w, &h, &bw, &d);
  return (w < 32 || h < 30);
}


/* Grabs an image (from a file, video, or the desktop) and renders it on
   the Drawable.  If `file' is specified, always use that file.  Otherwise,
   select randomly, based on the other arguments.
 */
static void
get_image (Screen *screen,
           Window window, Drawable drawable,
           Bool verbose_p,
           Bool desk_p,
           Bool video_p,
           Bool image_p,
           const char *dir,
           const char *file)
{
  Display *dpy = DisplayOfScreen (screen);
  grab_type which = GRAB_BARS;
  struct stat st;
  const char *file_prop = 0;
  char *absfile = 0;
  XRectangle geom = { 0, 0, 0, 0 };

  if (! drawable_window_p (dpy, window))
    {
      fprintf (stderr, "%s: 0x%lx is a pixmap, not a window!\n",
               progname, (unsigned long) window);
      exit (1);
    }

  /* Make sure the Screen and the Window correspond. */
  {
    XWindowAttributes xgwa;
    XGetWindowAttributes (dpy, window, &xgwa);
    screen = xgwa.screen;
  }

  if (file && stat (file, &st))
    {
      fprintf (stderr, "%s: file \"%s\" does not exist\n", progname, file);
      file = 0;
    }

  if (verbose_p)
    {
      fprintf (stderr, "%s: grabDesktopImages:  %s\n",
               progname, desk_p ? "True" : "False");
      fprintf (stderr, "%s: grabVideoFrames:    %s\n",
               progname, video_p ? "True" : "False");
      fprintf (stderr, "%s: chooseRandomImages: %s\n",
               progname, image_p ? "True" : "False");
      fprintf (stderr, "%s: imageDirectory:     %s\n",
               progname, (file ? file : dir ? dir : ""));
    }

# if !(defined(HAVE_GDK_PIXBUF) || defined(HAVE_JPEGLIB))
  image_p = False;    /* can't load images from files... */
#  ifdef USE_EXTERNAL_SCREEN_GRABBER
  desk_p = False;     /* ...or from desktops grabbed to files. */
#  endif

  if (file)
    {
      fprintf (stderr,
               "%s: image file loading not available at compile-time\n",
               progname);
      fprintf (stderr, "%s: can't load \"%s\"\n", progname, file);
      file = 0;
    }
# endif /* !(HAVE_GDK_PIXBUF || HAVE_JPEGLIB) */

  if (file)
    {
      desk_p = False;
      video_p = False;
      image_p = True;
    }
  else if (!dir || !*dir)
    {
      if (verbose_p && image_p)
        fprintf (stderr,
                 "%s: no imageDirectory: turning off chooseRandomImages.\n",
                 progname);
      image_p = False;
    }

  /* If the target drawable is really small, no good can come of that.
     Always do colorbars in that case.
   */
  if (drawable_miniscule_p (dpy, drawable))
    {
      desk_p  = False;
      video_p = False;
      image_p = False;
    }

# ifndef _VROOT_H_
#  error Error!  This file definitely needs vroot.h!
# endif

  /* We can grab desktop images (using the normal X11 method) if:
       - the window is the real root window;
       - the window is a toplevel window.
     We cannot grab desktop images that way if:
       - the window is a non-top-level window.

     Under X11 on MacOS, desktops are just like loaded image files.
     Under Cocoa on MacOS, this code is not used at all.
   */
# ifndef USE_EXTERNAL_SCREEN_GRABBER
  if (desk_p)
    {
      if (!top_level_window_p (screen, window))
        {
          desk_p = False;
          if (verbose_p)
            fprintf (stderr,
                    "%s: 0x%x not top-level: turning off grabDesktopImages.\n",
                     progname, (unsigned int) window);
        }
    }
# endif /* !USE_EXTERNAL_SCREEN_GRABBER */

  if (! (desk_p || video_p || image_p))
    which = GRAB_BARS;
  else
    {
      int i = 0;
      int n;
      /* Loop until we get one that's permitted.
         If files or video are permitted, do them more often
         than desktop.

             D+V+I: 10% + 45% + 45%.
             V+I:   50% + 50%
             D+V:   18% + 82%
             D+I:   18% + 82%
       */
    AGAIN:
      n = (random() % 100);
      if (++i > 300) abort();
      else if (desk_p  && n < 10) which = GRAB_DESK;   /* 10% */
      else if (video_p && n < 55) which = GRAB_VIDEO;  /* 45% */
      else if (image_p)           which = GRAB_FILE;   /* 45% */
      else goto AGAIN;
    }


  /* If we're to search a directory to find an image file, do so now.
   */
  if (which == GRAB_FILE && !file)
    {
      file = get_filename (screen, dir, verbose_p);
      if (!file)
        {
          which = GRAB_BARS;
          if (verbose_p)
            fprintf (stderr, "%s: no image files found.\n", progname);
        }
    }

  /* Now actually render something.
   */
  switch (which)
    {
    case GRAB_BARS:
      {
        XWindowAttributes xgwa;
      COLORBARS:
        if (verbose_p)
          fprintf (stderr, "%s: drawing colorbars.\n", progname);
        XGetWindowAttributes (dpy, window, &xgwa);
        colorbars (screen, xgwa.visual, drawable, xgwa.colormap);
        XSync (dpy, False);
        if (! file_prop) file_prop = "";

      }
      break;

    case GRAB_DESK:
      if (! display_desktop (screen, window, drawable, verbose_p, &geom))
        goto COLORBARS;
      file_prop = "desktop";
      break;

    case GRAB_FILE:
      if (*file && *file != '/')	/* pathname is relative to dir. */
        {
          if (absfile) free (absfile);
          absfile = malloc (strlen(dir) + strlen(file) + 10);
          strcpy (absfile, dir);
          if (dir[strlen(dir)-1] != '/')
            strcat (absfile, "/");
          strcat (absfile, file);
        }
      if (! display_file (screen, window, drawable, 
                          (absfile ? absfile : file),
                          verbose_p, &geom))
        goto COLORBARS;
      file_prop = file;
      break;

    case GRAB_VIDEO:
      if (! display_video (screen, window, drawable, verbose_p, &geom))
        goto COLORBARS;
      file_prop = "video";
      break;

    default:
      abort();
      break;
    }

  {
    Atom a = XInternAtom (dpy, XA_XSCREENSAVER_IMAGE_FILENAME, False);
    if (file_prop && *file_prop)
      {
        char *f2 = strdup (file_prop);

        /* Take the extension off of the file name. */
        /* Duplicated in utils/grabclient.c. */
        char *slash = strrchr (f2, '/');
        char *dot = strrchr ((slash ? slash : f2), '.');
        if (dot) *dot = 0;
        /* Replace slashes with newlines */
        /* while ((dot = strchr(f2, '/'))) *dot = '\n'; */
        /* Replace slashes with spaces */
        /* while ((dot = strchr(f2, '/'))) *dot = ' '; */

        XChangeProperty (dpy, window, a, XA_STRING, 8, PropModeReplace, 
                         (unsigned char *) f2, strlen(f2));
        free (f2);
      }
    else
      XDeleteProperty (dpy, window, a);

    a = XInternAtom (dpy, XA_XSCREENSAVER_IMAGE_GEOMETRY, False);
    if (geom.width > 0)
      {
        char gstr[30];
        sprintf (gstr, "%dx%d+%d+%d", geom.width, geom.height, geom.x, geom.y);
        XChangeProperty (dpy, window, a, XA_STRING, 8, PropModeReplace, 
                         (unsigned char *) gstr, strlen (gstr));
      }
    else
      XDeleteProperty (dpy, window, a);
  }

  if (absfile) free (absfile);
  XSync (dpy, False);
}


#ifdef DEBUG
static Bool
mapper (XrmDatabase *db, XrmBindingList bindings, XrmQuarkList quarks,
	XrmRepresentation *type, XrmValue *value, XPointer closure)
{
  int i;
  for (i = 0; quarks[i]; i++)
    {
      if (bindings[i] == XrmBindTightly)
	fprintf (stderr, (i == 0 ? "" : "."));
      else if (bindings[i] == XrmBindLoosely)
	fprintf (stderr, "*");
      else
	fprintf (stderr, " ??? ");
      fprintf(stderr, "%s", XrmQuarkToString (quarks[i]));
    }

  fprintf (stderr, ": %s\n", (char *) value->addr);

  return False;
}
#endif /* DEBUG */


#define USAGE "usage: %s [ -options... ] window-id [pixmap-id]\n"	      \
   "\n"									      \
   "    %s\n"								      \
   "\n"									      \
   "    %s puts an image on the given window or pixmap.\n"		      \
   "\n"									      \
   "    It is used by those xscreensaver demos that operate on images.\n"     \
   "    The image may be a file loaded from disk, a frame grabbed from\n"     \
   "    the system's video camera, or a screenshot of the desktop,\n"         \
   "    depending on command-line options or the ~/.xscreensaver file.\n"     \
   "\n"									      \
   "    Options include:\n"						      \
   "\n"									      \
   "      -display host:dpy.screen    which display to use\n"		      \
   "      -root                       draw to the root window\n"	      \
   "      -verbose                    print diagnostics\n"		      \
   "      -images  / -no-images       whether to allow image file loading\n"  \
   "      -video   / -no-video        whether to allow video grabs\n"	      \
   "      -desktop / -no-desktop      whether to allow desktop screen grabs\n"\
   "      -directory <path>           where to find image files to load\n"    \
   "      -file <filename>            load this image file\n"                 \
   "\n"									      \
   "    The XScreenSaver Control Panel (xscreensaver-demo) lets you set the\n"\
   "    defaults for these options in your ~/.xscreensaver file.\n"           \
   "\n"

int
main (int argc, char **argv)
{
  saver_preferences P;
  Widget toplevel;
  Display *dpy;
  Screen *screen;
  char *oprogname = progname;
  char *file = 0;
  char version[255];

  Window window = (Window) 0;
  Drawable drawable = (Drawable) 0;
  const char *window_str = 0;
  const char *drawable_str = 0;
  char *s;
  int i;

  progname = argv[0];
  s = strrchr (progname, '/');
  if (s) progname = s+1;
  oprogname = progname;

  /* half-assed way of avoiding buffer-overrun attacks. */
  if (strlen (progname) >= 100) progname[100] = 0;

# ifndef _VROOT_H_
#  error Error!  This file definitely needs vroot.h!
# endif

  /* Get the version number, for error messages. */
  {
    char *v = (char *) strdup(strchr(screensaver_id, ' '));
    char *s1, *s2, *s3, *s4;
    s1 = (char *) strchr(v,  ' '); s1++;
    s2 = (char *) strchr(s1, ' ');
    s3 = (char *) strchr(v,  '('); s3++;
    s4 = (char *) strchr(s3, ')');
    *s2 = 0;
    *s4 = 0;
    sprintf (version, "Part of XScreenSaver %s -- %s.", s1, s3);
    free(v);
  }

  /* We must read exactly the same resources as xscreensaver.
     That means we must have both the same progclass *and* progname,
     at least as far as the resource database is concerned.  So,
     put "xscreensaver" in argv[0] while initializing Xt.
   */
  progname = argv[0] = "xscreensaver";

  /* allow one dash or two. */
  for (i = 1; i < argc; i++)
    if (argv[i][0] == '-' && argv[i][1] == '-') argv[i]++;

  toplevel = XtAppInitialize (&app, progclass, 0, 0, &argc, argv,
                              defaults, 0, 0);
  dpy = XtDisplay (toplevel);
  screen = XtScreen (toplevel);
  db = XtDatabase (dpy);
  XtGetApplicationNameAndClass (dpy, &s, &progclass);
  XSetErrorHandler (x_ehandler);
  XSync (dpy, False);

  /* Randomize -- only need to do this here because this program
     doesn't use the `screenhack.h' or `lockmore.h' APIs. */
# undef ya_rand_init
  ya_rand_init (0);

  memset (&P, 0, sizeof(P));
  P.db = db;
  load_init_file (dpy, &P);

  progname = argv[0] = oprogname;

  for (i = 1; i < argc; i++)
    {
      unsigned long w;
      char dummy;

      /* Have to re-process these, or else the .xscreensaver file
         has priority over the command line...
       */
      if (!strcmp (argv[i], "-v") || !strcmp (argv[i], "-verbose"))
        P.verbose_p = True;
      else if (!strcmp (argv[i], "-desktop"))    P.grab_desktop_p = True;
      else if (!strcmp (argv[i], "-no-desktop")) P.grab_desktop_p = False;
      else if (!strcmp (argv[i], "-video"))      P.grab_video_p = True;
      else if (!strcmp (argv[i], "-no-video"))   P.grab_video_p = False;
      else if (!strcmp (argv[i], "-images"))     P.random_image_p = True;
      else if (!strcmp (argv[i], "-no-images"))  P.random_image_p = False;
      else if (!strcmp (argv[i], "-file"))       file = argv[++i];
      else if (!strcmp (argv[i], "-directory") || !strcmp (argv[i], "-dir"))
        P.image_directory = argv[++i];
      else if (!strcmp (argv[i], "-root") || !strcmp (argv[i], "root"))
        {
          if (window)
            {
              fprintf (stderr, "%s: both %s and %s specified?\n",
                       progname, argv[i], window_str);
              goto LOSE;
            }
          window_str = argv[i];
          window = VirtualRootWindowOfScreen (screen);
        }
      else if ((1 == sscanf (argv[i], " 0x%lx %c", &w, &dummy) ||
                1 == sscanf (argv[i], " %lu %c",   &w, &dummy)) &&
               w != 0)
        {
          if (drawable)
            {
              fprintf (stderr, "%s: both %s and %s specified?\n",
                       progname, drawable_str, argv[i]);
              goto LOSE;
            }
          else if (window)
            {
              drawable_str = argv[i];
              drawable = (Drawable) w;
            }
          else
            {
              window_str = argv[i];
              window = (Window) w;
            }
        }
      else
        {
          if (argv[i][0] == '-')
            fprintf (stderr, "\n%s: unknown option \"%s\"\n",
                     progname, argv[i]);
          else
            fprintf (stderr, "\n%s: unparsable window/pixmap ID: \"%s\"\n",
                     progname, argv[i]);
        LOSE:
# ifdef __GNUC__
          __extension__   /* don't warn about "string length is greater than
                             the length ISO C89 compilers are required to
                             support" in the usage string... */
# endif
          fprintf (stderr, USAGE, progname, version, progname);
          exit (1);
        }
    }

  if (window == 0)
    {
      fprintf (stderr, "\n%s: no window ID specified!\n", progname);
      goto LOSE;
    }


#ifdef DEBUG
  if (P.verbose_p)       /* Print out all the resources we can see. */
    {
      XrmName name = { 0 };
      XrmClass class = { 0 };
      int count = 0;
      XrmEnumerateDatabase (db, &name, &class, XrmEnumAllLevels, mapper,
                            (XtPointer) &count);
    }
#endif /* DEBUG */

  if (!window) abort();
  if (!drawable) drawable = window;

  get_image (screen, window, drawable, P.verbose_p,
             P.grab_desktop_p, P.grab_video_p, P.random_image_p,
             P.image_directory, file);
  exit (0);
}