Question

I’ve got a simple C GTK Linux application that needs to set the background of the main window to an image from a GIF file. I done some reading and it appears that I should be able to do the following:

1- stuff the background image into a GdkPixbuf using gdk_pixbuf_new_from_file()
2- use gdk_pixbuf_render_pixmap_and_mask() to render the GdkPixbuf into a GdkPixMap
3- set the background of the GtkWindow using gdk_window_set_back_pixmap()

The call to gdk_window_set_back_pixmap() appears to require a GdKWindow instead of a GtkWindow. My code that isn’t working is below followed by my specific questions.

/*
 * Compile me with:
 *   gcc -o reels reels.c $(pkg-config --cflags --libs gtk+-2.0 gmodule-2.0)
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <time.h>

/* GTK */
#include <gdk/gdkx.h>
#include <gtk/gtk.h>

/**** prototypes ****/
static void destroy (GtkWidget*, gpointer);
GdkPixbuf *create_pixbuf(const gchar * filename);
/********************/

GtkWidget   *images[3][5];

static void destroy (GtkWidget *window, gpointer data)
{
  gtk_main_quit ();
}


GdkPixbuf *create_pixbuf(const gchar * filename)
{
   GdkPixbuf *pixbuf;
   GError *error = NULL;
   pixbuf = gdk_pixbuf_new_from_file(filename, &error);
   if(!pixbuf) {
      fprintf(stderr, "%s\n", error->message);
      g_error_free(error);
   }

   return pixbuf;
}


int main (int argc, char *argv[])
{
  GtkWidget *window, *table;
    GdkPixbufAnimation *animation;
    GtkWidget *image;
    int x,y;    
    GdkPixbuf *pixBuf;
    GdkPixmap *pixMap;

    gtk_init (&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_window_set_default_size (GTK_WINDOW (window), 628, 530);
  gtk_window_set_title (GTK_WINDOW (window), "Demo");
  gtk_container_set_border_width (GTK_CONTAINER (window), 10);
    //gtk_window_set_decorated( GTK_WINDOW(window), FALSE );

    pixBuf = create_pixbuf("background.gif");
    gdk_pixbuf_render_pixmap_and_mask(pixBuf, &pixMap, NULL, 255);
    gdk_window_set_back_pixmap( GDK_WINDOW (window), pixMap, (gboolean) TRUE);



#if 0
    /*  some code I found that is supposed to create a background image..
        Can't seem to get it converted correctly into 'C'
    */    

area=gtk.Drawingarea()

pixbuf=gtk.gdk.pixbuf_new_from_file('background.png')
pixmap, mask=pixbuf.render_pixmap_and_mask()

area.window.set_back_pixmap(pixmap, False)
#endif     

  g_signal_connect (G_OBJECT (window), "destroy", G_CALLBACK (destroy), NULL);
  table = gtk_table_new (3, 5, TRUE);

    /* setup animated gifs */
    for( y = 0; y < 3; y++ )
    {
        for( x = 0; x < 5; x++ )
        {
            /* set each Image widget to spin GIF */
            images[y][x] = gtk_image_new_from_file("spinning.gif");;
            gtk_table_attach (GTK_TABLE (table), images[y][x], x, x+1, y, y+1,    GTK_EXPAND, GTK_SHRINK, 0, 0);            
        }
    }

  /* Add five pixels of spacing between every row and every column. */
  gtk_table_set_row_spacings (GTK_TABLE (table), 5);
  gtk_table_set_col_spacings (GTK_TABLE (table), 5);

  gtk_container_add (GTK_CONTAINER (window), table);
  gtk_widget_show_all (window);

  gtk_main ();

  return 0;
}

The code compiles and runs but I get the following runtime errors ( which I expected since I don’t know how to derive a GdkWindow from a GtkWindow:

(reels:10951): GLib-GObject-WARNING **: invalid cast from GtkWindow'
toGdkWindow’

(reels:10951): Gdk-CRITICAL **: gdk_window_set_back_pixmap: assertion
`GDK_IS_WINDOW (window)’ failed

My questions are:

1- How do I derive a GdkWindow from the codes main window ( GtkWindow )?
2- Do I need to use a Drawing Area at all?
3- What do I need to do get the background.gif image displayed as the background on the main window?

Any help would be greatly appreciated. I’ve seen many snippets of code, but I’m having a hard time putting it all together, and I’m fairly new to Gtk still.

Answer 1

My questions are:

1- How do I derive a GdkWindow from the codes main window ( GtkWindow )?
2- Do I need to use a Drawing Area at all?
3- What do I need to do get the background.gif image displayed as the background on the main >window?

If you want set a image like a background in you gtk window, you should do:
1 – Load the image to a GdkPixbuf or variant. (gdk_pixbuf_new_from_file)
2 – Create a pixmap and a mask bitmap. (gdk_pixbuf_render_pixmap_and_mask () )
3 – Create a GtkStyle that hold style information for widgets.
4 – Load the render pixmap to the style.
5 – Set the GtkStyle to the main window.

An example:

#include <gtk/gtk.h>
#include <stdio.h>
#include <stdlib.h>

GdkPixbuf *load_pixbuf_from_file (const char *filename)
{
    GError *error = NULL;
    GdkPixbuf *pixbuf = gdk_pixbuf_new_from_file (filename, &error);

    if (pixbuf == NULL)
    {
        g_print ("Error loading file: %d : %s\n", error->code, error->message);
        g_error_free (error);
        exit (1);
    }
    return pixbuf;
}

GdkPixbufAnimation *load_pixbuf_animation_from_file (const char *filename)
{
    GError *error = NULL;
    GdkPixbufAnimation *pixbuf = gdk_pixbuf_animation_new_from_file (filename, &error);

    if (pixbuf == NULL)
    {
        g_print ("Error loading file: %d : %s\n", error->code, error->message);
        g_error_free (error);
        exit (1);   
    }
    return pixbuf;
}

int main (int argc, char **argv)
{
    GtkWidget *window = NULL;
    GdkPixbuf *image = NULL;
    GdkPixbufAnimation * anim = NULL;
    GtkWidget *widget = NULL;
    GdkPixmap *background = NULL;
    GtkStyle *style = NULL;

    gtk_init (&argc, &argv);
    /* Load a non animated gif */
    image = load_pixbuf_from_file ("/home/midnigther/Desktop/pict.gif");
    //  widget = gtk_image_new_from_pixbuf (image);
    gdk_pixbuf_render_pixmap_and_mask (image, &background, NULL, 0);
    style = gtk_style_new ();
    style->bg_pixmap [0] = background;
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title (GTK_WINDOW(window), "Load Image");
    gtk_window_set_default_size (GTK_WINDOW (window), 400, 300);
    gtk_widget_set_style (GTK_WIDGET(window), GTK_STYLE (style));
    gtk_window_set_transient_for (GTK_WINDOW (window), NULL);

    GtkWidget *hbox = NULL;
    hbox = gtk_hbox_new (0, FALSE);
    gtk_container_add (GTK_CONTAINER(window), hbox);

    GtkWidget *button = NULL;
    button = gtk_button_new_with_label ("Sonic");
    gtk_box_pack_start (GTK_BOX (hbox), button, FALSE, FALSE, 0);

    gtk_widget_show_all (window);
    gtk_main ();
    return 0;
}