How does one set the background of a GtkWindow to an image

cgtk

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.

Best Answer

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;
}

Setting a bit

Use the bitwise OR operator (|) to set a bit.

number |= 1UL << n;

That will set the nth bit of number. n should be zero, if you want to set the 1st bit and so on upto n-1, if you want to set the nth bit.

Use 1ULL if number is wider than unsigned long; promotion of 1UL << n doesn't happen until after evaluating 1UL << n where it's undefined behaviour to shift by more than the width of a long. The same applies to all the rest of the examples.

Clearing a bit

Use the bitwise AND operator (&) to clear a bit.

number &= ~(1UL << n);

That will clear the nth bit of number. You must invert the bit string with the bitwise NOT operator (~), then AND it.

Toggling a bit

The XOR operator (^) can be used to toggle a bit.

number ^= 1UL << n;

That will toggle the nth bit of number.

Checking a bit

You didn't ask for this, but I might as well add it.

To check a bit, shift the number n to the right, then bitwise AND it:

bit = (number >> n) & 1U;

That will put the value of the nth bit of number into the variable bit.

Changing the nth bit to x

Setting the nth bit to either 1 or 0 can be achieved with the following on a 2's complement C++ implementation:

number ^= (-x ^ number) & (1UL << n);

Bit n will be set if x is 1, and cleared if x is 0. If x has some other value, you get garbage. x = !!x will booleanize it to 0 or 1.

To make this independent of 2's complement negation behaviour (where -1 has all bits set, unlike on a 1's complement or sign/magnitude C++ implementation), use unsigned negation.

number ^= (-(unsigned long)x ^ number) & (1UL << n);

unsigned long newbit = !!x;    // Also booleanize to force 0 or 1
number ^= (-newbit ^ number) & (1UL << n);

It's generally a good idea to use unsigned types for portable bit manipulation.

number = (number & ~(1UL << n)) | (x << n);

(number & ~(1UL << n)) will clear the nth bit and (x << n) will set the nth bit to x.

It's also generally a good idea to not to copy/paste code in general and so many people use preprocessor macros (like the community wiki answer further down) or some sort of encapsulation.

Best Answer

Related Solutions

How to determine the size of the array in C

C++ – How to set, clear, and toggle a single bit

Setting a bit

Clearing a bit

Toggling a bit

Checking a bit

Changing the nth bit to x

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