help drawing

[MC_Vai <estoy ver megared net mx>]

	Hi,
	I want to draw a black square, which later I'll use
	as an oscilloscope, in my app but since I have not
	worked with drawables (so far), I decided to take a
	look at some code in a similar program ("pitchtune"
	was the chosen one).

	This is how I'm doing it:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/* file1.c */
GdkGC	*black_gc;

void
set_colors( GdkWindow	*win )
{
	GdkColor        color;
	GdkColormap     *colormap;

	colormap = gdk_window_get_colormap( win );
	gdk_colormap_ref( colormap );

	black_gc = gdk_gc_new( win );
	color.red = color.green = color.blue = 0;
	gdk_color_alloc( colormap, &color );
	gdk_gc_set_foreground( black_gc, &color );

	gdk_window_set_background( win, &color );
	gdk_colormap_unref( colormap );
}

/* file2.c */
extern GtkWidget	*area;
extern GdkImage		*image;

gint
area_callback(  GtkWidget	*widget,
		GdkEventExpose	*event )
{
	gdk_draw_image( area, black_gc, image,
			event->area.x, event->area.y,
			event->area.x, event->area.y,
			event->area.width, event->area.height );

	return TRUE;
}


/* file3.c */
#define	IMAGE_WIDTH	350
#define	IMAGE_HEIGHT	150

GtkWidget	*area;
GdkVisual	*visual;
GdkImage	*image;

[...]
area = gtk_drawing_area_new();
gtk_widget_set_usize( area, IMAGE_WIDTH, IMAGE_HEIGHT );
gtk_signal_connect( GTK_OBJECT(area), "expose_event",
		GTK_SIGNAL_FUNC(area_callback), NULL );
[...]
gtk_widget_realize( area );
visual = gdk_window_get_visual( area->window );
gdk_visual_ref( visual );

set_colors( area->window );

gdk_visual_unref( visual );
image = gdk_image_new(  GDK_IMAGE_FASTEST,
			visual,
			IMAGE_WIDTH,
			IMAGE_HEIGHT );
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


	But the program runs (at the start) inmediately
	crashes and I get this message:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gdk-ERROR **: BadValue (integer parameter out of range for operation)
serial 595 error_code 2 request_code 143 minor_code 3
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	If somebody could point me to what this error means...
	what am I missing?
	This is the first time I'm working with drawables and I
	have no clue on how to fix this?

	Thanks a lot in advance for your help.
	Regards,

	                                 - Eduardo.