Re: How to create a GdkImage from a file.

[muppet <scott asofyet org>]

Please direct questions like this to gtk-app-devel- 
list gnome org ...  gtk-devel-list is for discussion of the  
development *of* gtk+, not *with* it.


On Dec 20, 2006, at 8:35 AM, Prasanna Kumar K wrote:

> I want to genetate a GdkImage from a file .. (so that this GdkImage  
> can be passed to gdk_draw_image())
> I used following calls..
>
> GtkImage *gtk_image = NULL;
> GdkImage *gdk_image = NULL;
> GdkBitmap *gdk_bitmap = NULL;
>
> gtk_image_set_from_file (gtk_image, "1.jpg");
> gtk_image_set_from_image (gtk_image, gdk_image, gdk_bitmap);
> gdk_draw_image (pixmap,  widget->style->white_gc,  gdk_image,
>                               0, 0,  60, 60, 100, 100);
>
>
> but while running the appliction I'm getting following error..
>  Gtk-CRITICAL **: gtk_image_set_from_file: assertion `GTK_IS_IMAGE  
> (image)' failed
>
> can anyone tell what is the problem.

Firstly, you're passing NULL for the image to set_from_image(); it  
doesn't like that.

GtkImage != GdkImage.  GtkImage is a widget that displays images.   
GdkImage is basically a wrapper for XImage, which is a client-side  
image resource.

You're also calling set_image() instead of get_image().  You could do  
this sort of thing:

    gtk_image_set_from_file (gtk_image, filename);
    gtk_image_get_image (gtk_image, &gdk_image, &mask);

but that's very wasteful, using the GtkImage just to perform I/O for  
you.

Instead, I think what you actually want is to use a GdkPixbuf, which  
is a 24-bit client-side resource that is easier to use than  
GdkImage.  It goes something like this:

    GdkPixbuf * pixbuf;
    GError * error = NULL;

    pixbuf = gdk_pixbuf_new_from_file ("1.jpg", &error);
    if (pixbuf) {
        gdk_draw_pixbuf (pixmap, widget->style->fg_gc, pixbuf,
                         0, 0, dest_x, dest_y,
                         gdk_pixbuf_get_width (pixbuf),
                         gdk_pixbuf_get_height (pixbuf,
                         GDK_RGB_DITHER_NORMAL,
                         dest_x, dest_y);
    } else {
        /* error contains failure info */
    }