Re: GdkPixmap and GdkPixbuf

[y g <odysseus lost gmail com>]

On 6/6/05, David Necas (Yeti) <yeti physics muni cz> wrote:
> On Mon, Jun 06, 2005 at 03:22:51PM +0100, y g wrote:
> > after following the scribble example on the Gtk tutorial I try to save
> > the image produced. Looking on the documentation of GdkPixbuf I found
> > I could use the following which however gives me a segmentation fault
> > in my program.
> >
> > static GdkPixmap *pixmap = NULL;
> > gdk_pixbuf_save(GDK_PIXBUF(pixmap), "temp.bmp", "bmp", NULL);
> >
> > I know that pixmap is of type of GdkPixmap and that arg 1 of the
> > function must be a GDK_PIXBUF and hence the cast. But as I said I am
> > getting a segmentation fault. Any clues why?
>
> No matter the bad typecast, you are trying to save a NULL
> pointer.  So what else you can expect than a segfault?
Sorry for that my fault as i wasn't very clear, It is a global and
initialised as null but it is assigned later.

> And to the bad typecast.  Neither of GdkPixbuf, GdkPixmap is
> a child of the other.  See gdk_pixbuf_get_from_drawable()
> for how to get a GdkPixbuf from a drawable.
I already did as I realised that neither is a child of the other as
you say. But I am still get seg fault with the following:

static void
save_image(GtkWidget* widget, gpointer user_data)
{
 GdkPixbuf* pixbuf;

 g_print("Saving image...\n");
 //gdk_pixbuf_save(gdk_pixbuf_get_from_drawable(NULL,
GDK_DRAWABLE(pixmap), NULL, 0, 0, 0, 0, 600, 400), "temp.bmp", "bmp",
NULL);
 gdk_pixbuf_get_from_drawable(pixbuf, GDK_DRAWABLE(pixmap), NULL, 0,
0, 0, 0, 600, 400);
 gdk_pixbuf_save(pixbuf, "temp.bmp", "bmp", NULL);
}




Here is the full program, not big, just the scribble from what I
understood of it.

#include <gtk/gtk.h>
#include <gdk/gdk.h>


/* Backing pixmap for drawing area */
static GdkPixmap *pixmap = NULL;


static void
save_image(GtkWidget* widget, gpointer user_data)
{
 GdkPixbuf* pixbuf;

 g_print("Saving image...\n");
 //gdk_pixbuf_save(gdk_pixbuf_get_from_drawable(NULL,
GDK_DRAWABLE(pixmap), NULL, 0, 0, 0, 0, 600, 400), "temp.bmp", "bmp",
NULL);
 gdk_pixbuf_get_from_drawable(pixbuf, GDK_DRAWABLE(pixmap), NULL, 0,
0, 0, 0, 600, 400);
 gdk_pixbuf_save(pixbuf, "temp.bmp", "bmp", NULL);
}


/* Draw a rectangle on the screen */
static void
draw_brush (GtkWidget *widget, gdouble x, gdouble y)
{
 g_print("draw_brush\n");

 GdkRectangle update_rect;

 update_rect.x = x - 5;
 update_rect.y = y - 5;
 update_rect.width = 10;
 update_rect.height = 10;
 gdk_draw_rectangle (pixmap,
                     widget->style->black_gc,
                     TRUE,
                     update_rect.x, update_rect.y,
                     update_rect.width, update_rect.height);
 gtk_widget_queue_draw_area (widget,
                             update_rect.x, update_rect.y,
                             update_rect.width, update_rect.height);

}


/* Redraw the screen from the backing pixmap */
static gboolean
expose_event( GtkWidget *widget, GdkEventExpose *event )
{
 g_print("expose_event\n");

 gdk_draw_drawable(widget->window,
                   widget->style->fg_gc[GTK_WIDGET_STATE (widget)],
                   pixmap,
                   event->area.x, event->area.y,
                   event->area.x, event->area.y,
                   event->area.width, event->area.height);

 return FALSE;
}




/* Create a new backing pixmap of the appropriate size */
static gboolean
configure_event( GtkWidget *widget, GdkEventConfigure *event )
{
 g_print("configure_event\n");

 if (pixmap)
   g_object_unref(pixmap);

 pixmap = gdk_pixmap_new(widget->window,
                         widget->allocation.width,
                         widget->allocation.height,
                         -1);
 gdk_draw_rectangle (pixmap,
                     widget->style->white_gc,
                     TRUE,
                     0, 0,
                     widget->allocation.width,
                     widget->allocation.height);

 return TRUE;
}


static gboolean
button_press_event( GtkWidget *widget, GdkEventButton *event )
{
 g_print("button_press_event\n");

 if (event->button == 1 && pixmap != NULL)
     draw_brush (widget, event->x, event->y);

 return TRUE;
}

static gboolean
motion_notify_event( GtkWidget *widget, GdkEventMotion *event )
{
 int x, y;
 GdkModifierType state;

 g_print("motion_notify_event\n");

 if (event->is_hint)
   gdk_window_get_pointer (event->window, &x, &y, &state);
 else
   {
     x = event->x;
     y = event->y;
     state = event->state;
   }

 if (state & GDK_BUTTON1_MASK && pixmap != NULL)
   draw_brush (widget, x, y);

 return TRUE;
}


int
main(int argc, char *argv[])
{
 GtkWidget* main;
 GtkWidget* drawing_area;
 GtkWidget* vbox1;
 GtkWidget* buttonSave;

 gtk_set_locale ();
 gtk_init (&argc, &argv);

 main = gtk_window_new(GTK_WINDOW_TOPLEVEL);
 gtk_window_set_title(GTK_WINDOW(main), "Drawing area");

 vbox1 = gtk_vbox_new (FALSE, 0);
 gtk_widget_show (vbox1);
 gtk_container_add (GTK_CONTAINER (main), vbox1);

 drawing_area = gtk_drawing_area_new();
 gtk_drawing_area_size(GTK_DRAWING_AREA(drawing_area), 600, 400);
 gtk_box_pack_start (GTK_BOX (vbox1), drawing_area, TRUE, TRUE, 0);
 //gtk_container_add(GTK_CONTAINER(main), drawing_area);

 buttonSave = gtk_button_new_from_stock ("gtk-save");
 gtk_box_pack_start (GTK_BOX (vbox1), buttonSave, FALSE, FALSE, 0);

 gtk_signal_connect (GTK_OBJECT (drawing_area), "expose_event",
                     (GtkSignalFunc) expose_event, NULL);
 gtk_signal_connect (GTK_OBJECT(drawing_area),"configure_event",
                     (GtkSignalFunc) configure_event, NULL);
 gtk_signal_connect (GTK_OBJECT (drawing_area), "motion_notify_event",
                     (GtkSignalFunc) motion_notify_event, NULL);
 gtk_signal_connect (GTK_OBJECT (drawing_area), "button_press_event",
                     (GtkSignalFunc) button_press_event, NULL);
 gtk_signal_connect (GTK_OBJECT (buttonSave), "clicked",
                     (GtkSignalFunc) save_image, NULL);

 gtk_widget_set_events (drawing_area, GDK_EXPOSURE_MASK
                        | GDK_LEAVE_NOTIFY_MASK
                        | GDK_BUTTON_PRESS_MASK
                        | GDK_POINTER_MOTION_MASK
                        | GDK_POINTER_MOTION_HINT_MASK);

 gtk_widget_show(vbox1);
 gtk_widget_show(drawing_area);
 gtk_widget_show(buttonSave);
 gtk_widget_show(main);
 gtk_main();
 return 0;
}