path: root/eel/eel-background.c

/* -*- Mode: C; indent-tabs-mode: t; c-basic-offset: 8; tab-width: 8 -*-

   eel-background.c: Object for the background of a widget.
 
   Copyright (C) 2000 Eazel, Inc.
  
   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.
  
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.
  
   You should have received a copy of the GNU Library General Public
   License along with this program; if not, write to the
   Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.
  
   Author: Darin Adler <darin@eazel.com>
*/

#include <config.h>
#include "eel-background.h"
#include "eel-gdk-extensions.h"
#include "eel-gdk-pixbuf-extensions.h"
#include "eel-glib-extensions.h"
#include "eel-gnome-extensions.h"
#include "eel-gtk-macros.h"
#include "eel-lib-self-check-functions.h"
#include "eel-string.h"
#include "eel-marshal.h"
#include "eel-types.h"
#include "eel-type-builtins.h"
#include <gtk/gtk.h>
#include <eel/eel-canvas.h>
#include <eel/eel-canvas-util.h>
#include <gio/gio.h>
#include <math.h>
#include <stdio.h>
#define GNOME_DESKTOP_USE_UNSTABLE_API
#include <libgnomeui/gnome-bg.h>

static void       eel_background_class_init                (gpointer       klass);
static void       eel_background_init                      (gpointer       object,
							    gpointer       klass);
static void       eel_background_finalize                  (GObject       *object);
static GdkPixmap *eel_background_get_pixmap_and_color      (EelBackground *background,
							    GdkWindow     *window,
							    GdkColor      *color,
							    gboolean      *changes_with_size);
static void set_image_properties (EelBackground *background);

EEL_CLASS_BOILERPLATE (EelBackground, eel_background, GTK_TYPE_OBJECT)

enum {
	APPEARANCE_CHANGED,
	SETTINGS_CHANGED,
	RESET,
	LAST_SIGNAL
};

/* This is the size of the GdkRGB dither matrix, in order to avoid
 * bad dithering when tiling the gradient
 */
#define GRADIENT_PIXMAP_TILE_SIZE 128

static guint signals[LAST_SIGNAL];

struct EelBackgroundDetails {
	char *color;
	
	GnomeBG *bg;

	/* Realized data: */
	gboolean background_changes_with_size;
	GdkPixmap *background_pixmap;
	int background_entire_width;
	int background_entire_height;
	GdkColor default_color;

	gboolean use_base;
	
	/* Is this background attached to desktop window */
	gboolean is_desktop;
	/* Desktop screen size watcher */
	gulong screen_size_handler;
	/* Can we use common pixmap for root window and desktop window */
	gboolean use_common_pixmap;
};

static void
eel_background_class_init (gpointer klass)
{
	GObjectClass *object_class;

	object_class = G_OBJECT_CLASS (klass);

	eel_type_init ();

	signals[APPEARANCE_CHANGED] =
		g_signal_new ("appearance_changed",
			      G_TYPE_FROM_CLASS (object_class),
			      G_SIGNAL_RUN_LAST | G_SIGNAL_NO_RECURSE,
			      G_STRUCT_OFFSET (EelBackgroundClass,
					       appearance_changed),
			      NULL, NULL,
			      g_cclosure_marshal_VOID__VOID,
			      G_TYPE_NONE,
			      0);
	signals[SETTINGS_CHANGED] =
		g_signal_new ("settings_changed",
			      G_TYPE_FROM_CLASS (object_class),
			      G_SIGNAL_RUN_LAST | G_SIGNAL_NO_RECURSE,
			      G_STRUCT_OFFSET (EelBackgroundClass,
					       settings_changed),
			      NULL, NULL,
			      g_cclosure_marshal_VOID__INT,
			      G_TYPE_NONE,
			      1, G_TYPE_INT);
	signals[RESET] =
		g_signal_new ("reset",
			      G_TYPE_FROM_CLASS (object_class),
			      G_SIGNAL_RUN_LAST | G_SIGNAL_NO_RECURSE,
			      G_STRUCT_OFFSET (EelBackgroundClass,
					       reset),
			      NULL, NULL,
			      g_cclosure_marshal_VOID__VOID,
			      G_TYPE_NONE,
			      0);

	object_class->finalize = eel_background_finalize;
}

static void
on_bg_changed (GnomeBG *bg, EelBackground *background)
{
	g_signal_emit (G_OBJECT (background),
		       signals[APPEARANCE_CHANGED], 0);
}

static void
eel_background_init (gpointer object, gpointer klass)
{
	EelBackground *background;

	background = EEL_BACKGROUND (object);

	background->details = g_new0 (EelBackgroundDetails, 1);
	background->details->default_color.red = 0xffff;
	background->details->default_color.green = 0xffff;
	background->details->default_color.blue = 0xffff;
	background->details->bg = gnome_bg_new ();

	g_signal_connect (background->details->bg, "changed",
			  G_CALLBACK (on_bg_changed), background);
	
}

/* The safe way to clear an image from a background is:
 * 		eel_background_set_image_uri (NULL);
 * This fn is a private utility - it does NOT clear
 * the details->bg_uri setting.
 */
static void
eel_background_remove_current_image (EelBackground *background)
{
	if (background->details->bg != NULL) {
		g_object_unref (G_OBJECT (background->details->bg));
		background->details->bg = NULL;
	}
}

static void
eel_background_finalize (GObject *object)
{
	EelBackground *background;

	background = EEL_BACKGROUND (object);

	g_free (background->details->color);
	eel_background_remove_current_image (background);

	if (background->details->background_pixmap != NULL) {
		g_object_unref (background->details->background_pixmap);
		background->details->background_pixmap = NULL;
	}

	g_free (background->details);

	EEL_CALL_PARENT (G_OBJECT_CLASS, finalize, (object));
}

static EelBackgroundImagePlacement
placement_gnome_to_eel (GnomeBGPlacement p)
{
	switch (p) {
	case GNOME_BG_PLACEMENT_CENTERED:
		return EEL_BACKGROUND_CENTERED;
	case GNOME_BG_PLACEMENT_FILL_SCREEN:
		return EEL_BACKGROUND_SCALED;
	case GNOME_BG_PLACEMENT_SCALED:
		return EEL_BACKGROUND_SCALED_ASPECT;
	case GNOME_BG_PLACEMENT_ZOOMED:
		return EEL_BACKGROUND_ZOOM;
	case GNOME_BG_PLACEMENT_TILED:
		return EEL_BACKGROUND_TILED;
	}

	return EEL_BACKGROUND_TILED;
}

static GnomeBGPlacement
placement_eel_to_gnome (EelBackgroundImagePlacement p)
{
	switch (p) {
	case EEL_BACKGROUND_CENTERED:
		return GNOME_BG_PLACEMENT_CENTERED;
	case EEL_BACKGROUND_SCALED:
		return GNOME_BG_PLACEMENT_FILL_SCREEN;
	case EEL_BACKGROUND_SCALED_ASPECT:
		return GNOME_BG_PLACEMENT_SCALED;
	case EEL_BACKGROUND_ZOOM:
		return GNOME_BG_PLACEMENT_ZOOMED;
	case EEL_BACKGROUND_TILED:
		return GNOME_BG_PLACEMENT_TILED;
	}

	return GNOME_BG_PLACEMENT_TILED;
}

EelBackgroundImagePlacement
eel_background_get_image_placement (EelBackground *background)
{
	g_return_val_if_fail (EEL_IS_BACKGROUND (background), EEL_BACKGROUND_TILED);

	return placement_gnome_to_eel (gnome_bg_get_placement (background->details->bg));
}

void
eel_background_set_image_placement (EelBackground              *background,
				    EelBackgroundImagePlacement new_placement)
{
	g_return_if_fail (EEL_IS_BACKGROUND (background));

	gnome_bg_set_placement (background->details->bg,
				placement_eel_to_gnome (new_placement));
}

EelBackground *
eel_background_new (void)
{
	return EEL_BACKGROUND (g_object_new (EEL_TYPE_BACKGROUND, NULL));
}

static void
eel_background_unrealize (EelBackground *background)
{
	if (background->details->background_pixmap != NULL) {
		g_object_unref (background->details->background_pixmap);
		background->details->background_pixmap = NULL;
	}
	background->details->background_entire_width = 0;
	background->details->background_entire_height = 0;
	background->details->default_color.red = 0xffff;
	background->details->default_color.green = 0xffff;
	background->details->default_color.blue = 0xffff;
}

static void
drawable_get_adjusted_size (EelBackground *background,
			    GdkDrawable   *drawable,
			    int		  *width,
			    int	          *height)
{
	GdkScreen *screen;
	
	/* 
	 * Screen resolution change makes root drawable have incorrect size.
	 */    
	gdk_drawable_get_size (drawable, width, height);

	if (background->details->is_desktop) {
		screen = gdk_drawable_get_screen (drawable);
		*width = gdk_screen_get_width (screen);
		*height = gdk_screen_get_height (screen);
	}
}

static gboolean
eel_background_ensure_realized (EelBackground *background, GdkWindow *window)
{
	gpointer data;
	GtkWidget *widget;
	GtkStyle *style;
	gboolean changed;
	int entire_width;
	int entire_height;
	
	drawable_get_adjusted_size (background, window, &entire_width, &entire_height);
	
	/* Set the default color */
	
	/* Get the widget to which the window belongs and its style as well */
	gdk_window_get_user_data (window, &data);
	widget = GTK_WIDGET (data);
	if (widget != NULL) {
		style = gtk_widget_get_style (widget);
		if (background->details->use_base) {
			background->details->default_color = style->base[GTK_STATE_NORMAL];
		} else {
			background->details->default_color = style->bg[GTK_STATE_NORMAL];
		}
		
		gdk_rgb_find_color (style->colormap, &(background->details->default_color));
	}

	/* If the pixmap doesn't change with the window size, never update
	 * it again.
	 */
	if (background->details->background_pixmap != NULL &&
	    !background->details->background_changes_with_size) {
		return FALSE;
	}

	/* If the window size is the same as last time, don't update */
	if (entire_width == background->details->background_entire_width &&
	    entire_height == background->details->background_entire_height) {
		return FALSE;
	}

	if (background->details->background_pixmap != NULL) {
		g_object_unref (background->details->background_pixmap);
		background->details->background_pixmap = NULL;
	}

	changed = FALSE;

	set_image_properties (background);

	background->details->background_changes_with_size = gnome_bg_changes_with_size (background->details->bg);
	background->details->background_pixmap = gnome_bg_create_pixmap (background->details->bg,
									 window,
									 entire_width, entire_height,
									 background->details->is_desktop);

	changed = TRUE;
	
	
	background->details->background_entire_width = entire_width;
	background->details->background_entire_height = entire_height;
	
	return changed;
}

static GdkPixmap *
eel_background_get_pixmap_and_color (EelBackground *background,
				     GdkWindow     *window,
				     GdkColor      *color,
				     gboolean      *changes_with_size)
{
	int entire_width;
	int entire_height;

	drawable_get_adjusted_size (background, window, &entire_width, &entire_height);

	eel_background_ensure_realized (background, window);
	
	*color = background->details->default_color;
	*changes_with_size = background->details->background_changes_with_size;
	
	if (background->details->background_pixmap != NULL) {
		return g_object_ref (background->details->background_pixmap);
	} 
	return NULL;
}

void
eel_background_expose (GtkWidget                   *widget,
		       GdkEventExpose              *event)
{
	GdkColor color;
	int window_width;
	int window_height;
	gboolean changes_with_size;
	GdkPixmap *pixmap;
	GdkGC *gc;
	GdkGCValues gc_values;
	GdkGCValuesMask value_mask;

	EelBackground *background;
	
	if (event->window != widget->window) {
		return;
	}

	background = eel_get_widget_background (widget);

	drawable_get_adjusted_size (background, widget->window, &window_width, &window_height);
	
	pixmap = eel_background_get_pixmap_and_color (background,
						      widget->window,
						      &color,
						      &changes_with_size);

        if (!changes_with_size) {
                /* The background was already drawn by X, since we set
                 * the GdkWindow background/back_pixmap.
                 * No need to draw it again. */
                if (pixmap) {
                        g_object_unref (pixmap);
                }
                return;
        }
 
	if (pixmap) {
		gc_values.tile = pixmap;
		gc_values.ts_x_origin = 0;
		gc_values.ts_y_origin = 0;
		gc_values.fill = GDK_TILED;
		value_mask = GDK_GC_FILL | GDK_GC_TILE | GDK_GC_TS_X_ORIGIN | GDK_GC_TS_Y_ORIGIN;
	} else {
		gdk_rgb_find_color (gtk_widget_get_colormap (widget), &color);
		gc_values.foreground = color;
		gc_values.fill = GDK_SOLID;
		value_mask = GDK_GC_FILL | GDK_GC_FOREGROUND;
	}
	
	gc = gdk_gc_new_with_values (widget->window, &gc_values, value_mask);
	
	gdk_gc_set_clip_rectangle (gc, &event->area);

	gdk_draw_rectangle (widget->window, gc, TRUE, 0, 0, window_width, window_height);
	
	g_object_unref (gc);
	
	if (pixmap) {
		g_object_unref (pixmap);
	}
}

static void
set_image_properties (EelBackground *background)
{
	if (!background->details->color) {
		gnome_bg_set_color (background->details->bg, GNOME_BG_COLOR_SOLID,
				 &background->details->default_color, NULL);
	} else if (!eel_gradient_is_gradient (background->details->color)) {
		GdkColor c;

		eel_gdk_color_parse_with_white_default (background->details->color, &c);
	
		gnome_bg_set_color (background->details->bg, GNOME_BG_COLOR_SOLID, &c, NULL);
	} else {
		GdkColor c1;
		GdkColor c2;
		char *spec;

		spec = eel_gradient_get_start_color_spec (background->details->color);
		eel_gdk_color_parse_with_white_default (spec, &c1);
		g_free (spec);

		spec = eel_gradient_get_end_color_spec (background->details->color);
		eel_gdk_color_parse_with_white_default (spec, &c2);
		g_free (spec);

		if (eel_gradient_is_horizontal (background->details->color))
			gnome_bg_set_color (background->details->bg, GNOME_BG_COLOR_H_GRADIENT, &c1, &c2);
		else
			gnome_bg_set_color (background->details->bg, GNOME_BG_COLOR_V_GRADIENT, &c1, &c2);

	}
}

char *
eel_background_get_color (EelBackground *background)
{
	g_return_val_if_fail (EEL_IS_BACKGROUND (background), NULL);

	return g_strdup (background->details->color);
}

char *
eel_background_get_image_uri (EelBackground *background)
{
	const char *filename;
	
	g_return_val_if_fail (EEL_IS_BACKGROUND (background), NULL);

	filename = gnome_bg_get_filename (background->details->bg);
	
	return g_filename_to_uri (filename, NULL, NULL);
}

/* Use style->base as the default color instead of bg */
void
eel_background_set_use_base (EelBackground *background,
			     gboolean use_base)
{
	background->details->use_base = use_base;
}

void
eel_background_set_color (EelBackground *background,
			  const char *color)
{
	if (eel_strcmp (background->details->color, color) != 0) {
		g_free (background->details->color);
		background->details->color = g_strdup (color);
		
		set_image_properties (background);
	}
}

static gboolean
eel_background_set_image_uri_helper (EelBackground *background,
				     const char *image_uri,
				     gboolean emit_signal)
{
	char *filename;

	if (image_uri != NULL) {
		filename = g_filename_from_uri (image_uri, NULL, NULL);
	}
	else {
		filename = NULL;
	}
	
	gnome_bg_set_filename (background->details->bg, filename);

	if (emit_signal) {
		g_signal_emit (GTK_OBJECT (background), signals[SETTINGS_CHANGED], 0, GDK_ACTION_COPY);
	}

	set_image_properties (background);
	
	g_free (filename);
	
	return TRUE;
}

void
eel_background_set_image_uri (EelBackground *background, const char *image_uri)
{
	
	
	eel_background_set_image_uri_helper (background, image_uri, TRUE);
}

/* Use this fn to set both the image and color and avoid flash. The color isn't
 * changed till after the image is done loading, that way if an update occurs
 * before then, it will use the old color and image.
 */
static void
eel_background_set_image_uri_and_color (EelBackground *background, GdkDragAction action,
					const char *image_uri, const char *color)
{
	eel_background_set_image_uri_helper (background, image_uri, FALSE);
	eel_background_set_color (background, color);

	/* We always emit, even if the color didn't change, because the image change
	 * relies on us doing it here.
	 */

	g_signal_emit (background, signals[SETTINGS_CHANGED], 0, action);
}

void
eel_background_receive_dropped_background_image (EelBackground *background,
						 GdkDragAction action,
						 const char *image_uri)
{
	/* Currently, we only support tiled images. So we set the placement.
	 * We rely on eel_background_set_image_uri_and_color to emit
	 * the SETTINGS_CHANGED & APPEARANCE_CHANGE signals.
	 */
	eel_background_set_image_placement (background, EEL_BACKGROUND_TILED);
	
	eel_background_set_image_uri_and_color (background, action, image_uri, NULL);
}

/**
 * eel_background_is_set:
 * 
 * Check whether the background's color or image has been set.
 */
gboolean
eel_background_is_set (EelBackground *background)
{
	g_assert (EEL_IS_BACKGROUND (background));

	return background->details->color != NULL
		|| gnome_bg_get_filename (background->details->bg) != NULL;
}

/**
 * eel_background_reset:
 *
 * Emit the reset signal to forget any color or image that has been
 * set previously.
 */
void
eel_background_reset (EelBackground *background)
{
	g_return_if_fail (EEL_IS_BACKGROUND (background));

	g_signal_emit (GTK_OBJECT (background), signals[RESET], 0);
}

static void
eel_background_set_up_widget (EelBackground *background, GtkWidget *widget)
{
	GtkStyle *style;
	GdkPixmap *pixmap;
	GdkPixmap *root_pixmap;
	GdkColor color;
	
	int window_width;
	int window_height;
	
	GdkWindow *window;
	gboolean changes_with_size;

	if (!GTK_WIDGET_REALIZED (widget)) {
		return;
	}

	drawable_get_adjusted_size (background, widget->window, &window_width, &window_height);
	
	pixmap = eel_background_get_pixmap_and_color (background,
						      widget->window,
						      &color, 
						      &changes_with_size);

	style = gtk_widget_get_style (widget);
	
	gdk_rgb_find_color (style->colormap, &color);

	if (EEL_IS_CANVAS (widget)) {
		window = GTK_LAYOUT (widget)->bin_window;
	} else {
		window = widget->window;
	}

	if (!changes_with_size || background->details->is_desktop) {
		gdk_window_set_back_pixmap (window, pixmap, FALSE);
	} else {
		gdk_window_set_back_pixmap (window, NULL, FALSE);
		gdk_window_set_background (window, &color);
	}
	

	background->details->background_changes_with_size =
		gnome_bg_changes_with_size (background->details->bg);
	
	if (background->details->is_desktop) {

		root_pixmap = NULL;

		if (background->details->use_common_pixmap) {
			root_pixmap = g_object_ref (pixmap);
		} else {
			root_pixmap = gnome_bg_create_pixmap (background->details->bg, window,
							      window_width, window_height, TRUE);
		}

		gnome_bg_set_pixmap_as_root (gdk_drawable_get_screen (window), root_pixmap);
		g_object_unref (root_pixmap);
	}
	
	if (pixmap) {
		g_object_unref (pixmap);
	}
}

static void
eel_widget_background_changed (GtkWidget *widget, EelBackground *background)
{
	eel_background_unrealize (background);
	eel_background_set_up_widget (background, widget);

	gtk_widget_queue_draw (widget);
}

/* Callback used when the style of a widget changes.  We have to regenerate its
 * EelBackgroundStyle so that it will match the chosen GTK+ theme.
 */
static void
widget_style_set_cb (GtkWidget *widget, GtkStyle *previous_style, gpointer data)
{
	EelBackground *background;
	
	background = EEL_BACKGROUND (data);
	
	eel_widget_background_changed (widget, background);
}

static void
screen_size_changed (GdkScreen *screen, EelBackground *background)
{
	g_signal_emit (background, signals[APPEARANCE_CHANGED], 0);
}


static void
widget_realized_setup (GtkWidget *widget, gpointer data)
{
	EelBackground *background;
	
	background = EEL_BACKGROUND (data);
	
        if (background->details->is_desktop) {
		GdkWindow *root_window;	
		GdkScreen *screen;
		
		screen = gtk_widget_get_screen (widget);

		if (background->details->screen_size_handler > 0) {
		        g_signal_handler_disconnect (screen,
				                     background->details->screen_size_handler);
		}
	
		background->details->screen_size_handler = 
			g_signal_connect (screen, "size_changed",
            				  G_CALLBACK (screen_size_changed), background);

		root_window = gdk_screen_get_root_window(screen);			
		
		if (gdk_drawable_get_visual (root_window) == gtk_widget_get_visual (widget)) {
			background->details->use_common_pixmap = TRUE;
		} else {
			background->details->use_common_pixmap = FALSE;
		}
	}
}

static void
widget_realize_cb (GtkWidget *widget, gpointer data)
{
	EelBackground *background;
	
	background = EEL_BACKGROUND (data);

	widget_realized_setup (widget, data);
		
	eel_background_set_up_widget (background, widget);
}

static void
widget_unrealize_cb (GtkWidget *widget, gpointer data)
{
	EelBackground *background;
	
	background = EEL_BACKGROUND (data);

	if (background->details->screen_size_handler > 0) {
		        g_signal_handler_disconnect (gtk_widget_get_screen (GTK_WIDGET (widget)),
				                     background->details->screen_size_handler);
			background->details->screen_size_handler = 0;
	}
	background->details->use_common_pixmap = FALSE;
}

void
eel_background_set_desktop (EelBackground *background, GtkWidget *widget, gboolean is_desktop)
{
	background->details->is_desktop = is_desktop;

	if (GTK_WIDGET_REALIZED(widget) && background->details->is_desktop) {
		widget_realized_setup (widget, background);
	}
	
}

gboolean
eel_background_is_desktop (EelBackground *background)
{
	return background->details->is_desktop;
}

/* Gets the background attached to a widget.

   If the widget doesn't already have a EelBackground object,
   this will create one. To change the widget's background, you can
   just call eel_background methods on the widget.

   If the widget is a canvas, nothing more needs to be done.  For
   normal widgets, you need to call eel_background_expose() from your
   expose handler to draw the background.

   Later, we might want a call to find out if we already have a background,
   or a way to share the same background among multiple widgets; both would
   be straightforward.
*/
EelBackground *
eel_get_widget_background (GtkWidget *widget)
{
	gpointer data;
	EelBackground *background;

	g_return_val_if_fail (GTK_IS_WIDGET (widget), NULL);

	/* Check for an existing background. */
	data = g_object_get_data (G_OBJECT (widget), "eel_background");
	if (data != NULL) {
		g_assert (EEL_IS_BACKGROUND (data));
		return data;
	}

	/* Store the background in the widget's data. */
	background = eel_background_new ();
	g_object_ref (background);
	gtk_object_sink (GTK_OBJECT (background));
	g_object_set_data_full (G_OBJECT (widget), "eel_background",
				background, g_object_unref);

	/* Arrange to get the signal whenever the background changes. */
	g_signal_connect_object (background, "appearance_changed",
				 G_CALLBACK (eel_widget_background_changed), widget, G_CONNECT_SWAPPED);
	eel_widget_background_changed (widget, background);

	g_signal_connect_object (widget, "style_set",
				 G_CALLBACK (widget_style_set_cb),
				 background,
				 0);
	g_signal_connect_object (widget, "realize",
				 G_CALLBACK (widget_realize_cb),
				 background,
				 0);
	g_signal_connect_object (widget, "unrealize",
				 G_CALLBACK (widget_unrealize_cb),
				 background,
				 0);

	return background;
}

/* determine if a background is darker or lighter than average, to help clients know what
   colors to draw on top with */
gboolean
eel_background_is_dark (EelBackground *background)
{
	return gnome_bg_is_dark (background->details->bg);
}
   
/* handle dropped colors */
void
eel_background_receive_dropped_color (EelBackground *background,
				      GtkWidget *widget,
				      GdkDragAction action,
				      int drop_location_x,
				      int drop_location_y,
				      const GtkSelectionData *selection_data)
{
	guint16 *channels;
	char *color_spec;
	char *new_gradient_spec;
	int left_border, right_border, top_border, bottom_border;

	g_return_if_fail (EEL_IS_BACKGROUND (background));
	g_return_if_fail (GTK_IS_WIDGET (widget));
	g_return_if_fail (selection_data != NULL);

	/* Convert the selection data into a color spec. */
	if (selection_data->length != 8 || selection_data->format != 16) {
		g_warning ("received invalid color data");
		return;
	}
	channels = (guint16 *) selection_data->data;
	color_spec = g_strdup_printf ("#%02X%02X%02X",
				      channels[0] >> 8,
				      channels[1] >> 8,
				      channels[2] >> 8);

	/* Figure out if the color was dropped close enough to an edge to create a gradient.
	   For the moment, this is hard-wired, but later the widget will have to have some
	   say in where the borders are.
	*/
	left_border = 32;
	right_border = widget->allocation.width - 32;
	top_border = 32;
	bottom_border = widget->allocation.height - 32;
	if (drop_location_x < left_border && drop_location_x <= right_border) {
		new_gradient_spec = eel_gradient_set_left_color_spec (background->details->color, color_spec);
	} else if (drop_location_x >= left_border && drop_location_x > right_border) {
		new_gradient_spec = eel_gradient_set_right_color_spec (background->details->color, color_spec);
	} else if (drop_location_y < top_border && drop_location_y <= bottom_border) {
		new_gradient_spec = eel_gradient_set_top_color_spec (background->details->color, color_spec);
	} else if (drop_location_y >= top_border && drop_location_y > bottom_border) {
		new_gradient_spec = eel_gradient_set_bottom_color_spec (background->details->color, color_spec);
	} else {
		new_gradient_spec = g_strdup (color_spec);
	}
	
	g_free (color_spec);

	eel_background_set_image_uri_and_color (background, action, NULL, new_gradient_spec);

	g_free (new_gradient_spec);
}

void
eel_background_save_to_gconf (EelBackground *background)
{
	GConfClient *client = gconf_client_get_default ();

	if (background->details->bg)
		gnome_bg_save_to_preferences (background->details->bg, client);
}

/* self check code */

#if !defined (EEL_OMIT_SELF_CHECK)

void
eel_self_check_background (void)
{
	EelBackground *background;

	background = eel_background_new ();

	eel_background_set_color (background, NULL);
	eel_background_set_color (background, "");
	eel_background_set_color (background, "red");
	eel_background_set_color (background, "red-blue");
	eel_background_set_color (background, "red-blue:h");

	gtk_object_sink (GTK_OBJECT (background));
}

#endif