gimp/plug-ins/common/waves.c

/**************************************************
 * file: waves/waves.c
 *
 * Copyright (c) 1997 Eric L. Hernes (erich@rrnet.com)
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. The name of the author may not be used to endorse or promote products
 *    derived from this software withough specific prior written permission
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * $Id$
 */

#include "config.h"

#include <string.h>
#include <stdlib.h>

#ifdef __GNUC__
#warning GTK_DISABLE_DEPRECATED
#endif
#undef GTK_DISABLE_DEPRECATED

#include <gtk/gtk.h>

#include <libgimp/gimp.h>
#include <libgimp/gimpui.h>

#include "libgimp/stdplugins-intl.h"


enum
{
  MODE_SMEAR,
  MODE_BLACKEN
};

typedef struct 
{
  gdouble amplitude;
  gdouble phase;
  gdouble wavelength;
  gint32  type;
  gint32  reflective;
} piArgs;

/*  preview stuff -- to be removed as soon as we have a real libgimp preview  */

typedef struct 
{
  gint     width;
  gint     height;
  gint     bpp;
  gdouble  scale;
  guchar  *bits;
} mwPreview;

#define PREVIEW_SIZE 100

static gint do_preview = TRUE;

static GtkWidget *mw_preview_new (GtkWidget *parent,
				  mwPreview *mwp);
static mwPreview *mw_preview_build (GimpDrawable *drawable);

static mwPreview *mwp;


static void query (void);
static void run   (gchar      *name,
		   gint        nparam,
		   GimpParam  *param,
		   gint       *nretvals,
		   GimpParam **retvals);

static gint pluginCore       (piArgs *argp,
			      gint32  drawable);
static gint pluginCoreIA     (piArgs *argp,
			      gint32  drawable);

static void waves_do_preview (GtkWidget     *preview);

static void wave (guchar  *src,
		  guchar  *dest,
		  gint     width,
		  gint     height,
		  gint     bypp,
		  gdouble  amplitude,
		  gdouble  wavelength,
		  gdouble  phase,
		  gint     smear,
		  gint     reflective,
		  gint     verbose);

static guchar bilinear (gdouble x,
			gdouble y,
			guchar *v);

#define WITHIN(a, b, c) ((((a) <= (b)) && ((b) <= (c))) ? TRUE : FALSE)

GimpPlugInInfo PLUG_IN_INFO =
{
  NULL,  /* init_proc  */
  NULL,  /* quit_proc  */
  query, /* query_proc */
  run,   /* run_proc   */
};

MAIN ()

static void
query (void)
{
  static GimpParamDef args[] =
  {
    { GIMP_PDB_INT32, "run_mode", "Interactive, non-interactive" },
    { GIMP_PDB_IMAGE, "image", "The Image" },
    { GIMP_PDB_DRAWABLE, "drawable", "The Drawable" },
    { GIMP_PDB_FLOAT, "amplitude", "The Amplitude of the Waves" },
    { GIMP_PDB_FLOAT, "phase", "The Phase of the Waves" },
    { GIMP_PDB_FLOAT, "wavelength", "The Wavelength of the Waves" },
    { GIMP_PDB_INT32, "type", "Type of waves, black/smeared" },
    { GIMP_PDB_INT32, "reflective", "Use Reflection" }
  };

  gimp_install_procedure ("plug_in_waves",
			  "Distort the image with waves",
			  "none yet",
			  "Eric L. Hernes, Stephen Norris",
			  "Stephen Norris",
			  "1997",
			  N_("<Image>/Filters/Distorts/Waves..."),
			  "RGB*, GRAY*",
			  GIMP_PLUGIN,
			  G_N_ELEMENTS (args), 0,
			  args, NULL);
}

static void
run (gchar      *name,
     gint        nparam,
     GimpParam  *param,
     gint       *nretvals,
     GimpParam **retvals)
{
  static GimpParam rvals[1];

  piArgs args;

  *nretvals = 1;
  *retvals  = rvals;

  rvals[0].type          = GIMP_PDB_STATUS;
  rvals[0].data.d_status = GIMP_PDB_SUCCESS;

  memset (&args, (int) 0, sizeof (piArgs));
  args.type = -1;
  gimp_get_data ("plug_in_waves", &args);

  switch (param[0].data.d_int32)
    {
      GimpDrawable *drawable;

    case GIMP_RUN_INTERACTIVE:
      INIT_I18N_UI();
      /* XXX: add code here for interactive running */
      if (args.type == -1)
	{
	  args.amplitude  = 10.0;
	  args.wavelength = 10;
	  args.phase      = 0.0;
	  args.type       = MODE_SMEAR;
	  args.reflective = 0;
	}

      drawable = gimp_drawable_get (param[2].data.d_drawable);
      mwp = mw_preview_build (drawable);

      if (pluginCoreIA(&args, param[2].data.d_drawable) == -1)
	{
	  rvals[0].data.d_status = GIMP_PDB_EXECUTION_ERROR;
	}
      else
	{
	  gimp_set_data ("plug_in_waves", &args, sizeof (piArgs));
	}

    break;

    case GIMP_RUN_NONINTERACTIVE:
      INIT_I18N();
      /* XXX: add code here for non-interactive running */
      if (nparam != 8)
	{
	  rvals[0].data.d_status = GIMP_PDB_CALLING_ERROR;
	  break;
	}
      args.amplitude  = param[3].data.d_float;
      args.phase      = param[4].data.d_float;
      args.wavelength = param[5].data.d_float;
      args.type       = param[6].data.d_int32;
      args.reflective = param[7].data.d_int32;

      if (pluginCore (&args, param[2].data.d_drawable) == -1)
	{
	  rvals[0].data.d_status = GIMP_PDB_EXECUTION_ERROR;
	  break;
	}
    break;

    case GIMP_RUN_WITH_LAST_VALS:
      INIT_I18N();
      /* XXX: add code here for last-values running */
      if (pluginCore (&args, param[2].data.d_drawable) == -1)
	{
	  rvals[0].data.d_status = GIMP_PDB_EXECUTION_ERROR;
	}
      break;
    }
}

static gint
pluginCore (piArgs *argp,
	    gint32  drawable)
{
  gint retval=0;
  GimpDrawable *drw;
  GimpPixelRgn srcPr, dstPr;
  guchar *src, *dst;
  guint width, height, Bpp;

  drw = gimp_drawable_get (drawable);

  width = drw->width;
  height = drw->height;
  Bpp = drw->bpp;

  src = g_new (guchar, width * height * Bpp);
  dst = g_new (guchar, width * height * Bpp);
  gimp_pixel_rgn_init (&srcPr, drw, 0, 0, width, height, FALSE, FALSE);
  gimp_pixel_rgn_init (&dstPr, drw, 0, 0, width, height, TRUE, TRUE);
  gimp_pixel_rgn_get_rect (&srcPr, src, 0, 0, width, height);

  wave (src, dst, width, height, Bpp, argp->amplitude, argp->wavelength,
        argp->phase, argp->type==0, argp->reflective, 1);
  gimp_pixel_rgn_set_rect (&dstPr, dst, 0, 0, width, height);

  g_free (src);
  g_free (dst);

  gimp_drawable_flush (drw);
  gimp_drawable_merge_shadow (drw->drawable_id, TRUE);
  gimp_drawable_update (drw->drawable_id, 0, 0, width, height);

  gimp_displays_flush ();

  return retval;
}

static gboolean run_flag = FALSE;

static void
waves_ok_callback (GtkWidget *widget,
		   gpointer   data)
{
  run_flag = TRUE;

  gtk_widget_destroy (GTK_WIDGET (data));
}

static void
waves_toggle_button_update (GtkWidget *widget,
			    gpointer   data)
{
  gimp_toggle_button_update (widget, data);

  if (do_preview)
    waves_do_preview (NULL);
}

static void
waves_radio_button_update (GtkWidget *widget,
			   gpointer   data)
{
  gimp_radio_button_update (widget, data);

  if (do_preview && GTK_TOGGLE_BUTTON (widget)->active)
    waves_do_preview (NULL);
}

static void
waves_double_adjustment_update (GtkAdjustment *adjustment,
				gpointer   data)
{
  gimp_double_adjustment_update (adjustment, data);

  if (do_preview)
    waves_do_preview (NULL);
}

static gint
pluginCoreIA (piArgs *argp,
	      gint32         drawable)
{
  gint r=-1; /* default to error return */
  GtkWidget *dlg;
  GtkWidget *main_vbox;
  GtkWidget *frame;
  GtkWidget *hbox;
  GtkWidget *vbox;
  GtkWidget *sep;
  GtkWidget *table;
  GtkWidget *preview;
  GtkWidget *toggle;
  GtkObject *adj;

  gimp_ui_init ("waves", TRUE);

  dlg = gimp_dialog_new ( _("Waves"), "waves",
			 gimp_standard_help_func, "filters/waves.html",
			 GTK_WIN_POS_MOUSE,
			 FALSE, TRUE, FALSE,

			 GTK_STOCK_CANCEL, gtk_widget_destroy,
			 NULL, 1, NULL, FALSE, TRUE,
			 GTK_STOCK_OK, waves_ok_callback,
			 NULL, NULL, NULL, TRUE, FALSE,

			 NULL);

  g_signal_connect (G_OBJECT (dlg), "destroy",
                    G_CALLBACK (gtk_main_quit),
                    NULL);

  main_vbox = gtk_vbox_new (FALSE, 4);
  gtk_container_set_border_width (GTK_CONTAINER (main_vbox), 6);
  gtk_box_pack_start (GTK_BOX (GTK_DIALOG (dlg)->vbox), main_vbox,
		      TRUE, TRUE, 0);
  gtk_widget_show (main_vbox);

  hbox = gtk_hbox_new (FALSE, 4);
  gtk_box_pack_start (GTK_BOX (main_vbox), hbox, FALSE, FALSE, 0);
  gtk_widget_show (hbox);

  preview = mw_preview_new (hbox, mwp);
  g_object_set_data (G_OBJECT (preview), "piArgs", argp);
  waves_do_preview (preview);

  frame = gimp_radio_group_new2 (TRUE, _("Mode"),
				 G_CALLBACK (waves_radio_button_update),
				 &argp->type, (gpointer) argp->type,

				 _("_Smear"),   (gpointer) MODE_SMEAR, NULL,
				 _("_Blacken"), (gpointer) MODE_BLACKEN, NULL,

				 NULL);
  gtk_box_pack_start (GTK_BOX (hbox), frame, TRUE, TRUE, 0);
  gtk_widget_show (frame);

  vbox = GTK_BIN (frame)->child;

  sep = gtk_hseparator_new ();
  gtk_box_pack_start (GTK_BOX (vbox), sep, FALSE, FALSE, 2);
  gtk_widget_show (sep);

  toggle = gtk_check_button_new_with_mnemonic ( _("_Reflective"));
  gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (toggle), argp->reflective);
  gtk_box_pack_start (GTK_BOX (vbox), toggle, FALSE, FALSE, 0);
  gtk_widget_show (toggle);

  g_signal_connect (G_OBJECT (toggle), "toggled",
                    G_CALLBACK (waves_toggle_button_update),
                    &argp->reflective);

  frame = gtk_frame_new ( _("Parameter Settings"));
  gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_ETCHED_IN);
  gtk_box_pack_start (GTK_BOX (main_vbox), frame, FALSE, FALSE, 0);
  gtk_widget_show (frame);

  table = gtk_table_new (3, 3, FALSE);
  gtk_table_set_col_spacings (GTK_TABLE (table), 4);
  gtk_table_set_row_spacings (GTK_TABLE (table), 2);
  gtk_container_set_border_width (GTK_CONTAINER (table), 4);
  gtk_container_add (GTK_CONTAINER (frame), table);

  adj = gimp_scale_entry_new (GTK_TABLE (table), 0, 0,
			      _("_Amplitude:"), 140, 0,
			      argp->amplitude, 0.0, 101.0, 1.0, 5.0, 2,
			      TRUE, 0, 0,
			      NULL, NULL);
  g_signal_connect (G_OBJECT (adj), "value_changed",
                    G_CALLBACK (waves_double_adjustment_update),
                    &argp->amplitude);

  adj = gimp_scale_entry_new (GTK_TABLE (table), 0, 1,
			      _("_Phase:"), 140, 0,
			      argp->phase, 0.0, 360.0, 2.0, 5.0, 2,
			      TRUE, 0, 0,
			      NULL, NULL);
  g_signal_connect (G_OBJECT (adj), "value_changed",
                    G_CALLBACK (waves_double_adjustment_update),
                    &argp->phase);

  adj = gimp_scale_entry_new (GTK_TABLE (table), 0, 2,
			      _("_Wavelength:"), 140, 0,
			      argp->wavelength, 0.1, 50.0, 1.0, 5.0, 2,
			      TRUE, 0, 0,
			      NULL, NULL);
  g_signal_connect (G_OBJECT (adj), "value_changed",
                    G_CALLBACK (waves_double_adjustment_update),
                    &argp->wavelength);

  gtk_widget_show (table);

  gtk_widget_show (dlg);

  gtk_main ();
  gdk_flush ();

  if (run_flag)
    {
      return pluginCore (argp, drawable);
    }
  else
    {
      return r;
    }
}

static void
waves_do_preview (GtkWidget *widget)
{
  static GtkWidget *theWidget = NULL;
  piArgs *argp;
  guchar *dst;
  gint y;

  if (theWidget == NULL)
    {
      theWidget = widget;
    }

  argp = g_object_get_data (G_OBJECT (theWidget), "piArgs");
  dst = g_new (guchar, mwp->width * mwp->height * mwp->bpp);

  wave (mwp->bits, dst, mwp->width, mwp->height, mwp->bpp,
	(argp->amplitude / mwp->scale), (argp->wavelength / mwp->scale),
	argp->phase, argp->type == 0, argp->reflective, 0);

  for (y = 0; y < mwp->height; y++)
    {
      gtk_preview_draw_row (GTK_PREVIEW (theWidget),
			    dst + (y * mwp->width * mwp->bpp), 0, y,
			    mwp->width);
    }

  gtk_widget_queue_draw (theWidget);

  g_free (dst);
}

static void
mw_preview_toggle_callback (GtkWidget *widget,
                            gpointer   data)
{
  gimp_toggle_button_update (widget, data);

  if (do_preview)
    waves_do_preview (NULL);
}

static mwPreview *
mw_preview_build_virgin (GimpDrawable *drawable)
{
  mwPreview *mwp;

  mwp = g_new (mwPreview, 1);

  if (drawable->width > drawable->height)
    {
      mwp->scale  = (gdouble) drawable->width / (gdouble) PREVIEW_SIZE;
      mwp->width  = PREVIEW_SIZE;
      mwp->height = drawable->height / mwp->scale;
    }
  else
    {
      mwp->scale  = (gdouble) drawable->height / (gdouble) PREVIEW_SIZE;
      mwp->height = PREVIEW_SIZE;
      mwp->width  = drawable->width / mwp->scale;
    }

  mwp->bpp  = 3;
  mwp->bits = NULL;

  return mwp;
}

static mwPreview *
mw_preview_build (GimpDrawable *drawable)
{
  mwPreview *mwp;
  gint x, y, b;
  guchar *bc;
  guchar *drawableBits;
  GimpPixelRgn pr;

  mwp = mw_preview_build_virgin (drawable);

  gimp_pixel_rgn_init (&pr, drawable,
		       0, 0, drawable->width, drawable->height, FALSE, FALSE);
  drawableBits = g_new (guchar, drawable->width * drawable->bpp);

  bc = mwp->bits = g_new (guchar, mwp->width * mwp->height * mwp->bpp);
  for (y = 0; y < mwp->height; y++)
    {
      gimp_pixel_rgn_get_row (&pr, drawableBits,
			      0, (gint) (y * mwp->scale), drawable->width);

      for (x = 0; x < mwp->width; x++)
        {
          for (b = 0; b < mwp->bpp; b++)
            *bc++ = *(drawableBits +
                      ((gint) (x * mwp->scale) * drawable->bpp) +
		      b % drawable->bpp);
        }
    }
  g_free (drawableBits);

  return mwp;
}

static GtkWidget *
mw_preview_new (GtkWidget *parent,
                mwPreview *mwp)
{
  GtkWidget *preview;
  GtkWidget *frame;
  GtkWidget *pframe;
  GtkWidget *vbox;
  GtkWidget *button;

  frame = gtk_frame_new (_("Preview"));
  gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_ETCHED_IN);
  gtk_box_pack_start (GTK_BOX (parent), frame, FALSE, FALSE, 0);
  gtk_widget_show (frame);

  vbox = gtk_vbox_new (FALSE, 2);
  gtk_container_set_border_width (GTK_CONTAINER (vbox), 4);
  gtk_container_add (GTK_CONTAINER (frame), vbox);
  gtk_widget_show (vbox);

  pframe = gtk_frame_new (NULL);
  gtk_frame_set_shadow_type (GTK_FRAME(pframe), GTK_SHADOW_IN);
  gtk_box_pack_start (GTK_BOX (vbox), pframe, FALSE, FALSE, 0);
  gtk_widget_show (pframe);

  preview = gtk_preview_new (GTK_PREVIEW_COLOR);
  gtk_preview_size (GTK_PREVIEW (preview), mwp->width, mwp->height);
  gtk_container_add (GTK_CONTAINER (pframe), preview);
  gtk_widget_show (preview);

  button = gtk_check_button_new_with_mnemonic (_("_Do Preview"));
  gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button), do_preview);
  gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);
  gtk_widget_show (button);

  g_signal_connect (G_OBJECT (button), "toggled",
                    G_CALLBACK (mw_preview_toggle_callback),
                    &do_preview);

  return preview;
}


static void
wave (guchar  *src,
      guchar  *dst,
      gint     width,
      gint     height,
      gint     bypp,
      gdouble  amplitude,
      gdouble  wavelength,
      gdouble  phase,
      gint     smear,
      gint     reflective,
      gint     verbose)
{
  glong   rowsiz;
  guchar *p;
  guchar *dest;
  gint    x1, y1, x2, y2;
  gint    x, y;
  gint    prog_interval=0;
  gint    x1_in, y1_in, x2_in, y2_in;

  gdouble cen_x, cen_y;       /* Center of wave */
  gdouble xhsiz, yhsiz;       /* Half size of selection */
  gdouble radius, radius2;    /* Radius and radius^2 */
  gdouble amnt, d;
  gdouble needx, needy;
  gdouble dx, dy;
  gdouble xscale, yscale;

  gint xi, yi;

  guchar  values[4];
  guchar  val;

  gint k;

  phase = phase * G_PI / 180;
  rowsiz   = width * bypp;

  if (verbose)
    {
      gimp_progress_init (_("Waving..."));
      prog_interval=height/10;
    }

  x1 = y1 = 0;
  x2 = width;
  y2 = height;

  /* Wave the image.  For each pixel in the destination image
   * which is inside the selection, we compute the corresponding
   * waved location in the source image.  We use bilinear
   * interpolation to avoid ugly jaggies.
   *
   * Let's assume that we are operating on a circular area.
   * Every point within <radius> distance of the wave center is
   * waveed to its destination position.
   *
   * Basically, introduce a wave into the image. I made up the
   * forumla initially, but it looks good. Quartic added the
   * wavelength etc. to it while I was asleep :) Just goes to show
   * we should work with people in different time zones more.
   *
   */

  /* Center of selection */
  cen_x = (double) (x2 - 1 + x1) / 2.0;
  cen_y = (double) (y2 - 1 + y1) / 2.0;

  /* Compute wave radii (semiaxes) */
  xhsiz = (double) (x2 - x1) / 2.0;
  yhsiz = (double) (y2 - y1) / 2.0;

  /* These are the necessary scaling factors to turn the wave
     ellipse into a large circle */

  if (xhsiz < yhsiz)
    {
      xscale = yhsiz / xhsiz;
      yscale = 1.0;
    }
  else if (xhsiz > yhsiz)
    {
      xscale = 1.0;
      yscale = xhsiz / yhsiz;
    }
  else
    {
      xscale = 1.0;
      yscale = 1.0;
    }

  radius  = MAX (xhsiz, yhsiz);
  radius2 = radius * radius;

  /* Wave the image! */

  dst += y1 * rowsiz + x1 * bypp;

  wavelength *= 2;

  for (y = y1; y < y2; y++)
    {
      dest = dst;

      if (verbose && (y % prog_interval == 0))
	gimp_progress_update ((double) y / (double) height);

      for (x = x1; x < x2; x++)
	{
	  /* Distance from current point to wave center, scaled */
	  dx = (x - cen_x) * xscale;
	  dy = (y - cen_y) * yscale;

	  /* Distance^2 to center of *circle* (our scaled ellipse) */
	  d = sqrt (dx * dx + dy * dy);

	  /* Use the formula described above. */

	  /* Calculate waved point and scale again to ellipsify */

	  /*
	   * Reflective waves are strange - the effect is much
	   * more like a mirror which is in the shape of
	   * the wave than anything else.
	   */

	  if (reflective)
	    {
	      amnt = amplitude * fabs (sin (((d / wavelength) * (2.0 * G_PI) +
					     phase)));

	      needx = (amnt * dx) / xscale + cen_x;
	      needy = (amnt * dy) / yscale + cen_y;
	    }
	  else
	    {
	      amnt = amplitude * sin (((d / wavelength) * (2.0 * G_PI) +
				       phase));

	      needx = (amnt + dx) / xscale + cen_x;
	      needy = (amnt + dy) / yscale + cen_y;
	    }

	  /* Calculations complete; now copy the proper pixel */

	  xi = needx;
	  yi = needy;

	  if (smear)
	    {
	      if (xi > width - 2)
		{
		  xi = width - 2;
		}
	      else if (xi < 0)
		{
		  xi = 0;
		}
	      if (yi > height - 2)
		{
		  yi = height - 2;
		}
	      else if (yi < 0)
		{
		  yi = 0;
		}
	    }

	  p = src + rowsiz * yi + xi * bypp;

	  x1_in = WITHIN (0, xi, width - 1);
	  y1_in = WITHIN (0, yi, height - 1);
	  x2_in = WITHIN (0, xi + 1, width - 1);
	  y2_in = WITHIN (0, yi + 1, height - 1);

	  for (k = 0; k < bypp; k++)
	    {
	      if (x1_in && y1_in)
		values[0] = *(p + k);
	      else
		values[0] = 0;

	      if (x2_in && y1_in)
		values[1] = *(p + bypp + k);
	      else
		values[1] = 0;

	      if (x1_in && y2_in)
		values[2] = *(p + rowsiz + k);
	      else
		values[2] = 0;

	      if (x2_in)
		{
		  if (y2_in)
		    values[3] = *(p + bypp + k + rowsiz);
		  else
		    values[3] = 0;
		}
	      else
		values[3] = 0;

	      val = bilinear (needx, needy, values);

	      *dest++ = val;
	    }
	}

      dst += rowsiz;
    }

  if (verbose)
    gimp_progress_update (1.0);
}

static guchar
bilinear (gdouble  x,
	  gdouble  y,
	  guchar  *v)
{
  gdouble m0, m1;
  x = fmod (x, 1.0);
  y = fmod (y, 1.0);

  if (x < 0)
    x += 1.0;
  if (y < 0)
    y += 1.0;

  m0 = (1.0 - x) * v[0] + x * v[1];
  m1 = (1.0 - x) * v[2] + x * v[3];

  return (guchar) ((1.0 - y) * m0 + y * m1);
}