/* mate-bg-crossfade.h - fade window background between two surfaces
 *
 * Copyright (C) 2008 Red Hat, 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., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * Author: Ray Strode <rstrode@redhat.com>
*/
#include <string.h>
#include <math.h>
#include <stdarg.h>

#include <gio/gio.h>

#include <gdk/gdk.h>
#include <gdk/gdkx.h>
#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <gtk/gtk.h>

#include <cairo.h>
#include <cairo-xlib.h>

#define MATE_DESKTOP_USE_UNSTABLE_API
#include <mate-bg.h>
#include "mate-bg-crossfade.h"

struct _MateBGCrossfadePrivate
{
	GdkWindow       *window;
	GtkWidget       *widget;
	int              width;
	int              height;
	cairo_surface_t *fading_surface;
	cairo_surface_t *start_surface;
	cairo_surface_t *end_surface;
	gdouble          start_time;
	gdouble          total_duration;
	guint            timeout_id;
	guint            is_first_frame : 1;
};

enum {
	PROP_0,
	PROP_WIDTH,
	PROP_HEIGHT,
};

enum {
	FINISHED,
	NUMBER_OF_SIGNALS
};

static guint signals[NUMBER_OF_SIGNALS] = { 0 };

G_DEFINE_TYPE (MateBGCrossfade, mate_bg_crossfade, G_TYPE_OBJECT)
#define MATE_BG_CROSSFADE_GET_PRIVATE(o) (G_TYPE_INSTANCE_GET_PRIVATE ((o),\
			                   MATE_TYPE_BG_CROSSFADE,\
			                   MateBGCrossfadePrivate))

static void
mate_bg_crossfade_set_property (GObject      *object,
				 guint         property_id,
				 const GValue *value,
				 GParamSpec   *pspec)
{
	MateBGCrossfade *fade;

	g_assert (MATE_IS_BG_CROSSFADE (object));

	fade = MATE_BG_CROSSFADE (object);

	switch (property_id)
	{
	case PROP_WIDTH:
		fade->priv->width = g_value_get_int (value);
		break;
	case PROP_HEIGHT:
		fade->priv->height = g_value_get_int (value);
		break;
	default:
		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
		break;
	}
}

static void
mate_bg_crossfade_get_property (GObject    *object,
			     guint       property_id,
			     GValue     *value,
			     GParamSpec *pspec)
{
	MateBGCrossfade *fade;

	g_assert (MATE_IS_BG_CROSSFADE (object));

	fade = MATE_BG_CROSSFADE (object);

	switch (property_id)
	{
	case PROP_WIDTH:
		g_value_set_int (value, fade->priv->width);
		break;
	case PROP_HEIGHT:
		g_value_set_int (value, fade->priv->height);
		break;

	default:
		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
		break;
	}
}

static void
mate_bg_crossfade_finalize (GObject *object)
{
	MateBGCrossfade *fade;

	fade = MATE_BG_CROSSFADE (object);

	mate_bg_crossfade_stop (fade);

	if (fade->priv->fading_surface != NULL) {
		cairo_surface_destroy (fade->priv->fading_surface);
		fade->priv->fading_surface = NULL;
	}

	if (fade->priv->start_surface != NULL) {
		cairo_surface_destroy (fade->priv->start_surface);
		fade->priv->start_surface = NULL;
	}

	if (fade->priv->end_surface != NULL) {
		cairo_surface_destroy (fade->priv->end_surface);
		fade->priv->end_surface = NULL;
	}
}

static void
mate_bg_crossfade_class_init (MateBGCrossfadeClass *fade_class)
{
	GObjectClass *gobject_class;

	gobject_class = G_OBJECT_CLASS (fade_class);

	gobject_class->get_property = mate_bg_crossfade_get_property;
	gobject_class->set_property = mate_bg_crossfade_set_property;
	gobject_class->finalize = mate_bg_crossfade_finalize;

	/**
	 * MateBGCrossfade:width:
	 *
	 * When a crossfade is running, this is width of the fading
	 * surface.
	 */
	g_object_class_install_property (gobject_class,
					 PROP_WIDTH,
					 g_param_spec_int ("width",
						           "Window Width",
							    "Width of window to fade",
							    0, G_MAXINT, 0,
							    G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE));

	/**
	 * MateBGCrossfade:height:
	 *
	 * When a crossfade is running, this is height of the fading
	 * surface.
	 */
	g_object_class_install_property (gobject_class,
					 PROP_HEIGHT,
					 g_param_spec_int ("height", "Window Height",
						           "Height of window to fade on",
							   0, G_MAXINT, 0,
							   G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE));

	/**
	 * MateBGCrossfade::finished:
	 * @fade: the #MateBGCrossfade that received the signal
	 * @window: the #GdkWindow the crossfade happend on.
	 *
	 * When a crossfade finishes, @window will have a copy
	 * of the end surface as its background, and this signal will
	 * get emitted.
	 */
	signals[FINISHED] = g_signal_new ("finished",
					  G_OBJECT_CLASS_TYPE (gobject_class),
					  G_SIGNAL_RUN_LAST, 0, NULL, NULL,
					  g_cclosure_marshal_VOID__OBJECT,
					  G_TYPE_NONE, 1, G_TYPE_OBJECT);

	g_type_class_add_private (gobject_class, sizeof (MateBGCrossfadePrivate));
}

static void
mate_bg_crossfade_init (MateBGCrossfade *fade)
{
	fade->priv = MATE_BG_CROSSFADE_GET_PRIVATE (fade);

	fade->priv->window = NULL;
	fade->priv->widget = NULL;
	fade->priv->fading_surface = NULL;
	fade->priv->start_surface = NULL;
	fade->priv->end_surface = NULL;
	fade->priv->timeout_id = 0;
}

/**
 * mate_bg_crossfade_new:
 * @width: The width of the crossfading window
 * @height: The height of the crossfading window
 *
 * Creates a new object to manage crossfading a
 * window background between two #cairo_surface_ts.
 *
 * Return value: the new #MateBGCrossfade
 **/
MateBGCrossfade* mate_bg_crossfade_new (int width, int height)
{
	GObject* object;

	object = g_object_new(MATE_TYPE_BG_CROSSFADE,
		"width", width,
		"height", height,
		NULL);

	return (MateBGCrossfade*) object;
}

static cairo_surface_t *
tile_surface (cairo_surface_t *surface,
              int              width,
              int              height)
{
	cairo_surface_t *copy;
	cairo_t *cr;

	if (surface == NULL)
	{
		copy = gdk_window_create_similar_surface (gdk_get_default_root_window (),
		                                          CAIRO_CONTENT_COLOR,
		                                          width, height);
	}
	else
	{
		copy = cairo_surface_create_similar (surface,
		                                     cairo_surface_get_content (surface),
		                                     width, height);
	}

	cr = cairo_create (copy);

	if (surface != NULL)
	{
		cairo_pattern_t *pattern;
		cairo_set_source_surface (cr, surface, 0.0, 0.0);
		pattern = cairo_get_source (cr);
		cairo_pattern_set_extend (pattern, CAIRO_EXTEND_REPEAT);
	}
	else
	{
#if GTK_CHECK_VERSION (3, 0, 0)
		GtkStyleContext *context;
		GdkRGBA bg;
		context = gtk_style_context_new ();
		gtk_style_context_add_provider (context,
										GTK_STYLE_PROVIDER (gtk_css_provider_get_default ()),
										GTK_STYLE_PROVIDER_PRIORITY_THEME);
		gtk_style_context_get_background_color (context, GTK_STATE_FLAG_NORMAL, &bg);
		gdk_cairo_set_source_rgba(cr, &bg);
		g_object_unref (G_OBJECT (context));
#else
		GtkStyle *style;
		style = gtk_widget_get_default_style ();
		gdk_cairo_set_source_color(cr, &style->bg[GTK_STATE_NORMAL]);
#endif
	}

	cairo_paint (cr);

	if (cairo_status (cr) != CAIRO_STATUS_SUCCESS)
	{
		cairo_surface_destroy (copy);
		copy = NULL;
	}

	cairo_destroy(cr);

	return copy;
}

#if !GTK_CHECK_VERSION (3, 0, 0)
static cairo_surface_t *
tile_pixmap (GdkPixmap *pixmap,
             int        width,
             int        height)
{
	cairo_surface_t *copy;
	cairo_t *cr;

	copy = gdk_window_create_similar_surface (gdk_get_default_root_window (),
	                                          CAIRO_CONTENT_COLOR,
	                                          width, height);
	cr = cairo_create (copy);

	if (pixmap != NULL)
	{
		cairo_pattern_t *pattern;
		gdk_cairo_set_source_pixmap (cr, pixmap, 0.0, 0.0);
		pattern = cairo_get_source (cr);
		cairo_pattern_set_extend (pattern, CAIRO_EXTEND_REPEAT);
	}
	else
	{
		GtkStyle *style;
		style = gtk_widget_get_default_style ();
		gdk_cairo_set_source_color (cr, &style->bg[GTK_STATE_NORMAL]);
	}

	cairo_paint (cr);

	if (cairo_status (cr) != CAIRO_STATUS_SUCCESS)
	{
		cairo_surface_destroy (copy);
		copy = NULL;
	}

	cairo_destroy(cr);

	return copy;
}
#endif

/**
 * mate_bg_crossfade_set_start_surface:
 * @fade: a #MateBGCrossfade
 * @surface: The cairo surface to fade from
 *
 * Before initiating a crossfade with mate_bg_crossfade_start()
 * a start and end surface have to be set.  This function sets
 * the surface shown at the beginning of the crossfade effect.
 *
 * Return value: %TRUE if successful, or %FALSE if the surface
 * could not be copied.
 **/
gboolean
#if GTK_CHECK_VERSION(3, 0, 0)
mate_bg_crossfade_set_start_surface (MateBGCrossfade* fade, cairo_surface_t *surface)
#else
mate_bg_crossfade_set_start_pixmap (MateBGCrossfade* fade, GdkPixmap *pixmap)
#endif
{
	g_return_val_if_fail (MATE_IS_BG_CROSSFADE (fade), FALSE);

	if (fade->priv->start_surface != NULL)
	{
		cairo_surface_destroy (fade->priv->start_surface);
		fade->priv->start_surface = NULL;
	}

#if GTK_CHECK_VERSION(3, 0, 0)
	fade->priv->start_surface = tile_surface (surface,
#else
	fade->priv->start_surface = tile_pixmap  (pixmap,
#endif
	                                          fade->priv->width,
	                                          fade->priv->height);

	return fade->priv->start_surface != NULL;
}

static gdouble
get_current_time (void)
{
	const double microseconds_per_second = (double) G_USEC_PER_SEC;
	double timestamp;
	GTimeVal now;

	g_get_current_time (&now);

	timestamp = ((microseconds_per_second * now.tv_sec) + now.tv_usec) /
	            microseconds_per_second;

	return timestamp;
}

/**
 * mate_bg_crossfade_set_end_surface:
 * @fade: a #MateBGCrossfade
 * @surface: The cairo surface to fade to
 *
 * Before initiating a crossfade with mate_bg_crossfade_start()
 * a start and end surface have to be set.  This function sets
 * the surface shown at the end of the crossfade effect.
 *
 * Return value: %TRUE if successful, or %FALSE if the surface
 * could not be copied.
 **/
gboolean
#if GTK_CHECK_VERSION(3, 0, 0)
mate_bg_crossfade_set_end_surface (MateBGCrossfade* fade, cairo_surface_t *surface)
#else
mate_bg_crossfade_set_end_pixmap (MateBGCrossfade* fade, GdkPixmap *pixmap)
#endif
{
	g_return_val_if_fail (MATE_IS_BG_CROSSFADE (fade), FALSE);

	if (fade->priv->end_surface != NULL) {
		cairo_surface_destroy (fade->priv->end_surface);
		fade->priv->end_surface = NULL;
	}

#if GTK_CHECK_VERSION(3, 0, 0)
	fade->priv->end_surface = tile_surface (surface,
#else
	fade->priv->end_surface = tile_pixmap  (pixmap,
#endif
	                                        fade->priv->width,
	                                        fade->priv->height);

	/* Reset timer in case we're called while animating
	 */
	fade->priv->start_time = get_current_time ();
	return fade->priv->end_surface != NULL;
}

static gboolean
animations_are_disabled (MateBGCrossfade *fade)
{
	GtkSettings *settings;
	GdkScreen *screen;
	gboolean are_enabled;

	g_assert (fade->priv->window != NULL);

	screen = gdk_window_get_screen(fade->priv->window);

	settings = gtk_settings_get_for_screen (screen);

	g_object_get (settings, "gtk-enable-animations", &are_enabled, NULL);

	return !are_enabled;
}

static void
send_root_property_change_notification (MateBGCrossfade *fade)
{
        long zero_length_pixmap = 0;

        /* We do a zero length append to force a change notification,
         * without changing the value */
        XChangeProperty (GDK_WINDOW_XDISPLAY (fade->priv->window),
                         GDK_WINDOW_XID (fade->priv->window),
                         gdk_x11_get_xatom_by_name ("_XROOTPMAP_ID"),
                         XA_PIXMAP, 32, PropModeAppend,
                         (unsigned char *) &zero_length_pixmap, 0);
}

static void
draw_background (MateBGCrossfade *fade)
{
	if (fade->priv->widget != NULL) {
		gtk_widget_queue_draw (fade->priv->widget);
	} else if (gdk_window_get_window_type (fade->priv->window) != GDK_WINDOW_ROOT) {
#if GTK_CHECK_VERSION (3, 22, 0)
		cairo_t           *cr;
		cairo_region_t    *region;
		GdkDrawingContext *draw_context;

		region = gdk_window_get_visible_region (fade->priv->window);
		draw_context = gdk_window_begin_draw_frame (fade->priv->window,
		                                            region);
		cr = gdk_drawing_context_get_cairo_context (draw_context);
		cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
		cairo_set_source_surface (cr, fade->priv->fading_surface, 0, 0);
		cairo_paint (cr);
		gdk_window_end_draw_frame (fade->priv->window, draw_context);
		cairo_region_destroy (region);
#elif GTK_CHECK_VERSION (3, 0, 0)
		cairo_pattern_t *pattern;

		pattern =
		  cairo_pattern_create_for_surface (fade->priv->fading_surface);
		gdk_window_set_background_pattern (fade->priv->window, pattern);
		cairo_pattern_destroy (pattern);
		gdk_window_invalidate_rect (fade->priv->window, NULL, FALSE);
		gdk_window_process_updates (fade->priv->window, FALSE);
#else
		cairo_t   *cr;
		GdkPixmap *pixmap;

		pixmap = gdk_pixmap_new (fade->priv->window,
		                         fade->priv->width, fade->priv->height,
		                         -1);
		cr = gdk_cairo_create (pixmap);
		cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
		cairo_set_source_surface (cr, fade->priv->fading_surface, 0, 0);
		cairo_paint (cr);
		cairo_destroy (cr);
		gdk_window_set_back_pixmap (fade->priv->window, pixmap, FALSE);
		g_object_unref (pixmap);
		gdk_window_invalidate_rect (fade->priv->window, NULL, FALSE);
		gdk_window_process_updates (fade->priv->window, FALSE);
#endif
	} else {
		Display *xdisplay = GDK_WINDOW_XDISPLAY (fade->priv->window);
		gdk_error_trap_push ();
		XGrabServer (xdisplay);
		XClearWindow (xdisplay, GDK_WINDOW_XID (fade->priv->window));
		send_root_property_change_notification (fade);
		XFlush (xdisplay);
		XUngrabServer (xdisplay);
#if GTK_CHECK_VERSION (3, 0, 0)
		gdk_error_trap_pop_ignored ();
#else
		gdk_error_trap_pop ();
#endif
	}
}

static gboolean
on_widget_draw (GtkWidget       *widget,
#if GTK_CHECK_VERSION (3, 0, 0)
                cairo_t         *cr,
#else
                GdkEventExpose  *event,
#endif
                MateBGCrossfade *fade)
{
#if !GTK_CHECK_VERSION (3, 0, 0)
	cairo_t *cr;

#endif
	g_assert (fade->priv->fading_surface != NULL);

#if !GTK_CHECK_VERSION (3, 0, 0)
	cr = gdk_cairo_create (event->window);

	gdk_cairo_rectangle (cr, &event->area);
	cairo_clip (cr);

#endif
	cairo_set_source_surface (cr, fade->priv->fading_surface, 0, 0);
	cairo_pattern_set_extend (cairo_get_source (cr), CAIRO_EXTEND_REPEAT);
	cairo_paint (cr);

#if !GTK_CHECK_VERSION (3, 0, 0)
	cairo_destroy (cr);
#endif
	return FALSE;
}

static gboolean
on_tick (MateBGCrossfade *fade)
{
	gdouble now, percent_done;
	cairo_t *cr;
	cairo_status_t status;

	g_return_val_if_fail (MATE_IS_BG_CROSSFADE (fade), FALSE);

	now = get_current_time ();

	percent_done = (now - fade->priv->start_time) / fade->priv->total_duration;
	percent_done = CLAMP (percent_done, 0.0, 1.0);

	/* If it's taking a long time to get to the first frame,
	 * then lengthen the duration, so the user will get to see
	 * the effect.
	 */
	if (fade->priv->is_first_frame && percent_done > .33) {
		fade->priv->is_first_frame = FALSE;
		fade->priv->total_duration *= 1.5;
		return on_tick (fade);
	}

	if (fade->priv->fading_surface == NULL ||
	    fade->priv->end_surface == NULL) {
		return FALSE;
	}

	if (animations_are_disabled (fade)) {
		return FALSE;
	}

	/* We accumulate the results in place for performance reasons.
	 *
	 * This means 1) The fade is exponential, not linear (looks good!)
	 * 2) The rate of fade is not independent of frame rate. Slower machines
	 * will get a slower fade (but never longer than .75 seconds), and
	 * even the fastest machines will get *some* fade because the framerate
	 * is capped.
	 */
	cr = cairo_create (fade->priv->fading_surface);

	cairo_set_source_surface (cr, fade->priv->end_surface,
				  0.0, 0.0);
	cairo_paint_with_alpha (cr, percent_done);

	status = cairo_status (cr);
	cairo_destroy (cr);

	if (status == CAIRO_STATUS_SUCCESS) {
		draw_background (fade);
	}
	return percent_done <= .99;
}

static void
on_finished (MateBGCrossfade *fade)
{
	cairo_t *cr;

	if (fade->priv->timeout_id == 0)
		return;

	g_assert (fade->priv->fading_surface != NULL);
	g_assert (fade->priv->end_surface != NULL);

	cr = cairo_create (fade->priv->fading_surface);
	cairo_set_source_surface (cr, fade->priv->end_surface, 0, 0);
	cairo_paint (cr);
	cairo_destroy (cr);
	draw_background (fade);

	cairo_surface_destroy (fade->priv->fading_surface);
	fade->priv->fading_surface = NULL;

	cairo_surface_destroy (fade->priv->end_surface);
	fade->priv->end_surface = NULL;

	g_assert (fade->priv->start_surface != NULL);

	cairo_surface_destroy (fade->priv->start_surface);
	fade->priv->start_surface = NULL;

	if (fade->priv->widget != NULL) {
		g_signal_handlers_disconnect_by_func (fade->priv->widget,
		                                      (GCallback) on_widget_draw,
		                                      fade);
	}
	fade->priv->widget = NULL;

	fade->priv->timeout_id = 0;
	g_signal_emit (fade, signals[FINISHED], 0, fade->priv->window);
}

/* This function queries the _XROOTPMAP_ID property from the root window
 * to determine the current root window background pixmap and returns a
 * surface to draw directly to it.
 * If _XROOTPMAP_ID is not set, then NULL returned.
 */
static cairo_surface_t *
get_root_pixmap_id_surface (GdkDisplay *display)
{
	GdkScreen       *screen;
	Display         *xdisplay;
	Visual          *xvisual;
	Window           xroot;
	Atom             type;
	int              format, result;
	unsigned long    nitems, bytes_after;
	unsigned char   *data;
	cairo_surface_t *surface = NULL;

	g_return_val_if_fail (display != NULL, NULL);

	screen   = gdk_display_get_default_screen (display);
	xdisplay = GDK_DISPLAY_XDISPLAY (display);
	xvisual  = GDK_VISUAL_XVISUAL (gdk_screen_get_system_visual (screen));
	xroot    = RootWindow (xdisplay, GDK_SCREEN_XNUMBER (screen));

	result = XGetWindowProperty (xdisplay, xroot,
				     gdk_x11_get_xatom_by_name ("_XROOTPMAP_ID"),
				     0L, 1L, False, XA_PIXMAP,
				     &type, &format, &nitems, &bytes_after,
				     &data);

	if (result != Success || type != XA_PIXMAP ||
	    format != 32 || nitems != 1) {
		XFree (data);
		data = NULL;
	}

	if (data != NULL) {
		Pixmap pixmap = *(Pixmap *) data;
		Window root_ret;
		int x_ret, y_ret;
		unsigned int w_ret, h_ret, bw_ret, depth_ret;

		gdk_error_trap_push ();
		if (XGetGeometry (xdisplay, pixmap, &root_ret,
		                  &x_ret, &y_ret, &w_ret, &h_ret,
		                  &bw_ret, &depth_ret))
		{
			surface = cairo_xlib_surface_create (xdisplay,
			                                     pixmap, xvisual,
			                                     w_ret, h_ret);
		}

#if GTK_CHECK_VERSION (3, 0, 0)
		gdk_error_trap_pop_ignored ();
#else
		gdk_error_trap_pop ();
#endif
		XFree (data);
	}

	gdk_display_flush (display);
	return surface;
}

/**
 * mate_bg_crossfade_start:
 * @fade: a #MateBGCrossfade
 * @window: The #GdkWindow to draw crossfade on
 *
 * This function initiates a quick crossfade between two surfaces on
 * the background of @window. Before initiating the crossfade both
 * mate_bg_crossfade_set_start_surface() and
 * mate_bg_crossfade_set_end_surface() need to be called. If animations
 * are disabled, the crossfade is skipped, and the window background is
 * set immediately to the end surface.
 **/
void
mate_bg_crossfade_start (MateBGCrossfade *fade,
                         GdkWindow        *window)
{
	GSource *source;
	GMainContext *context;

	g_return_if_fail (MATE_IS_BG_CROSSFADE (fade));
	g_return_if_fail (window != NULL);
	g_return_if_fail (fade->priv->start_surface != NULL);
	g_return_if_fail (fade->priv->end_surface != NULL);
	g_return_if_fail (!mate_bg_crossfade_is_started (fade));
	g_return_if_fail (gdk_window_get_window_type (window) != GDK_WINDOW_FOREIGN);

	/* If drawing is done on the root window,
	 * it is essential to have the root pixmap.
	 */
	if (gdk_window_get_window_type (window) == GDK_WINDOW_ROOT) {
		GdkDisplay *display = gdk_window_get_display (window);
		cairo_surface_t *surface = get_root_pixmap_id_surface (display);

		g_return_if_fail (surface != NULL);
		cairo_surface_destroy (surface);
	}

	if (fade->priv->fading_surface != NULL) {
		cairo_surface_destroy (fade->priv->fading_surface);
		fade->priv->fading_surface = NULL;
	}

	fade->priv->window = window;
	if (gdk_window_get_window_type (fade->priv->window) != GDK_WINDOW_ROOT) {
		fade->priv->fading_surface = tile_surface (fade->priv->start_surface,
		                                           fade->priv->width,
		                                           fade->priv->height);
		if (fade->priv->widget != NULL) {
#if GTK_CHECK_VERSION (3, 0, 0)
			g_signal_connect (fade->priv->widget, "draw",
			                  (GCallback) on_widget_draw, fade);
#else
			g_signal_connect (fade->priv->widget, "expose-event",
			                  (GCallback) on_widget_draw, fade);
#endif
		}
	} else {
		cairo_t   *cr;
		GdkDisplay *display = gdk_window_get_display (fade->priv->window);

		fade->priv->fading_surface = get_root_pixmap_id_surface (display);
		cr = cairo_create (fade->priv->fading_surface);
		cairo_set_source_surface (cr, fade->priv->start_surface, 0, 0);
		cairo_paint (cr);
		cairo_destroy (cr);
	}
	draw_background (fade);

	source = g_timeout_source_new (1000 / 60.0);
	g_source_set_callback (source,
			       (GSourceFunc) on_tick,
			       fade,
			       (GDestroyNotify) on_finished);
	context = g_main_context_default ();
	fade->priv->timeout_id = g_source_attach (source, context);
	g_source_unref (source);

	fade->priv->is_first_frame = TRUE;
	fade->priv->total_duration = .75;
	fade->priv->start_time = get_current_time ();
}

/**
 * mate_bg_crossfade_start_widget:
 * @fade: a #MateBGCrossfade
 * @widget: The #GtkWidget to draw crossfade on
 *
 * This function initiates a quick crossfade between two surfaces on
 * the background of @widget. Before initiating the crossfade both
 * mate_bg_crossfade_set_start_surface() and
 * mate_bg_crossfade_set_end_surface() need to be called. If animations
 * are disabled, the crossfade is skipped, and the window background is
 * set immediately to the end surface.
 **/
void
mate_bg_crossfade_start_widget (MateBGCrossfade *fade,
                                GtkWidget       *widget)
{
	GdkWindow *window;

	g_return_if_fail (MATE_IS_BG_CROSSFADE (fade));
	g_return_if_fail (widget != NULL);

	fade->priv->widget = widget;
	gtk_widget_realize (fade->priv->widget);
	window = gtk_widget_get_window (fade->priv->widget);

	mate_bg_crossfade_start (fade, window);
}

/**
 * mate_bg_crossfade_is_started:
 * @fade: a #MateBGCrossfade
 *
 * This function reveals whether or not @fade is currently
 * running on a window.  See mate_bg_crossfade_start() for
 * information on how to initiate a crossfade.
 *
 * Return value: %TRUE if fading, or %FALSE if not fading
 **/
gboolean
mate_bg_crossfade_is_started (MateBGCrossfade *fade)
{
	g_return_val_if_fail (MATE_IS_BG_CROSSFADE (fade), FALSE);

	return fade->priv->timeout_id != 0;
}

/**
 * mate_bg_crossfade_stop:
 * @fade: a #MateBGCrossfade
 *
 * This function stops any in progress crossfades that may be
 * happening.  It's harmless to call this function if @fade is
 * already stopped.
 **/
void
mate_bg_crossfade_stop (MateBGCrossfade *fade)
{
	g_return_if_fail (MATE_IS_BG_CROSSFADE (fade));

	if (!mate_bg_crossfade_is_started (fade))
		return;

	g_assert (fade->priv->timeout_id != 0);
	g_source_remove (fade->priv->timeout_id);
	fade->priv->timeout_id = 0;
}