RE: Gnome Canvas Transparency

["Strong, Russell" <RStrong raytheon com au>]

#include <gnome.h>

static GnomeCanvasItem *zoom_group;

int timeout (gpointer data)
{
	static int count=0;
	double total[6],rotate[6],scale[6];

	art_affine_rotate (rotate, 0.5);
	if (count++ > 300)
		art_affine_scale (scale, 1.01, 1.01);
	else
		art_affine_scale (scale, 1.0/1.01, 1.0/1.01);
	if (count > 600)
		count = 0;
	art_affine_multiply (total, rotate, scale);

	/* rotate and scale the zoom_group of objects only */
	gnome_canvas_item_affine_relative (
		zoom_group,
		total);

	return -1;
}

void setup()
{
	GtkWidget *window;
	GtkWidget *canvas;
	GnomeCanvasItem *item, *grid;
	GnomeCanvasPathDef *path;

	window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
	gtk_widget_show (window);
	gtk_widget_set_usize (window, 500, 500);
	gtk_signal_connect (GTK_OBJECT (window), "destroy", gtk_main_quit,
NULL);

	canvas = gnome_canvas_new_aa();
	gtk_widget_show (canvas);
	gtk_container_add (GTK_CONTAINER (window), canvas);

	/* Add grid object to canvas first so that it is the first
	 * object drawn on the canvas, i.e. it is in the background
	 */
	grid = gnome_canvas_item_new (
		gnome_canvas_root (GNOME_CANVAS (canvas)),
		gnome_canvas_ellipse_get_type(),
		"fill_color", "red",
		"x1", -100.0,
		"y1", -100.0,
		"x2", 200.0,
		"y2", 200.0,
		NULL);
	gnome_canvas_item_show (grid);

	/* create zoom_group, this group will be zoomed and rotated
	 * and therefore so will all other objects that are "rooted" to
	 * this group object
	 */
	zoom_group = gnome_canvas_item_new (
		gnome_canvas_root (GNOME_CANVAS (canvas)),
		GNOME_TYPE_CANVAS_GROUP,
		NULL);
	gnome_canvas_item_show (zoom_group);

	path = gnome_canvas_path_def_new();
	gnome_canvas_path_def_moveto (path, 100, 100);
	gnome_canvas_path_def_lineto (path, 200, 100);
	gnome_canvas_path_def_lineto (path, 200, 200);
	gnome_canvas_path_def_curveto (path, 110, 100, 80,130, 100,100);
	gnome_canvas_path_def_closepath_current (path);
	
	item = gnome_canvas_item_new (
		GNOME_CANVAS_GROUP (zoom_group),
		GNOME_TYPE_CANVAS_SHAPE,
		"fill_color", "blue",
		"outline_color", "purple",
		NULL);
	gnome_canvas_shape_set_path_def (GNOME_CANVAS_SHAPE (item), path);
	gnome_canvas_item_show (item);

	gtk_timeout_add (20, timeout, NULL);
}

int main(int argc, char *argv[])
{
	gnome_init("chris garrett","1.0",argc,argv);

	setup();	
	
	gtk_main();
	return 0;
}


-----Original Message-----
From: Chris Garrett [mailto:garrett91 hotmail com]
Sent: Tuesday, 21 January 2003 23:49
To: gnome-devel-list gnome org
Subject: Gnome Canvas Transparency




Hi,

I have created a gnome canvas and I can display a pixbuf on it.  The pixbuf 
has an alpha channel, which is renders fine.

I would like to know how to put a chequered background on the canvas so that

it can be seen through transparent areas of the image.  I could add another 
pixbuf behind it, but then when the canvas is zoomed, so would the chequered

pixbuf (I want the squares to stay the same size, and to tile all the way 
across the canvas).

Any ideas?

Chris.

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