How to create a GtkImage from a Cairo context? - gtk

Question

I got a paint function that works using a Cairo context and the end result should be a GtkImage (without intermediate image creation). I tried to use the gdk_cairo_create function but this code:
...
GdkPixbuf *pixbuf = gdk_pixbuf_new (GDK_COLORSPACE_RGB, FALSE, 8, 22, 22);
GtkWidget *image = gtk_image_new_from_pixbuf (pixbuf);
GdkDrawable *drawable = image->window;
cairo_t *ctx = gdk_cairo_create (drawable);
my_cairo_paint_function (ctx);
...
fails with:
Gdk-CRITICAL **: IA__gdk_cairo_create: assertion `GDK_IS_DRAWABLE (drawable)' failed
Same with a simple:
#include <gtk/gtk.h>
#include <cairo.h>
int
main (int argc, char *argv[])
{
gtk_init(&argc, &argv);
cairo_t *ctx = gdk_cairo_create (gtk_widget_get_window (gtk_image_new_from_file ("foobar.png")));
gtk_main();
return 0;
}
I don't understand why this fails. Any help is appreciated!

Answer 1

GtkImage doesn't have a GdkWindow, so the call to gtk_widget_get_window() or the access of widget->window returns NULL. You can put the GtkImage in a GtkEventBox and draw on the event box's GdkWindow.
Although, it looks like you're trying (with gdk_pixbuf_new) to create an empty space to draw on. In that case, GtkImage is not the widget you want -- use GtkDrawingArea. And don't forget to call your paint function in the handler for the event-expose signal!