Drawing cairo with other widgets

qwertyui · **Joined:** Sat Sep 03, 2011 6:36 pm **Posts:** 94

My question is :

I want to draw something in the middle of a gtk window (programming in c gtk 2.24) with menubars and toolbars over it.
When i check this example on zetcode i try to add menubars and toolbars to the window but they overidde the other widgets.What i want to do is specify an area in the middle where its going to be drawn without messing around with the other widgets.To me it looks like the issue is cr = gdk_cairo_create(widget->window); where window should be replaced with an invisible widget but i dont have a clue since im new to cairo.

Code:

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

static gboolean
on_expose_event(GtkWidget *widget,
    GdkEventExpose *event,
    gpointer data)
{
  cairo_t *cr;
  cr = gdk_cairo_create(widget->window);

  gint i;
  for ( i = 1; i <= 10; i++) {
      cairo_set_source_rgba(cr, 0, 0, 1, i*0.1);
      cairo_rectangle(cr, 50*i, 20, 40, 40);
      cairo_fill(cr);  
  }

  cairo_destroy(cr);
  return FALSE;
}


int
main (int argc, char *argv[])
{
  GtkWidget *window;

  gtk_init(&argc, &argv);

  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);

  g_signal_connect(G_OBJECT(window), "expose-event",
      G_CALLBACK(on_expose_event), NULL);
  g_signal_connect(G_OBJECT(window), "destroy",
      G_CALLBACK(gtk_main_quit), NULL);

  gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
  gtk_window_set_default_size(GTK_WINDOW(window), 590, 90); 
  gtk_window_set_title(GTK_WINDOW(window), "transparency");

  gtk_widget_set_app_paintable(window, TRUE);
  gtk_widget_show_all(window);

  gtk_main();

  return 0;
}

Any suggestions?

Paul Childs · **Posted:** Thu Mar 01, 2012 10:15 am

No you want to leave widget->window as it is because its the window component of the widget structure that you want to get for a cairo context.
What you will find better is, rather than sending the whole window as the widget to be used by on_expose_event, create a Gtk Drawing Area in your window and then connect it to the on_expose_event handler. You then need to set a clip region so that drawing is confined to the window of the Drawing area (thus not messing with your other widgets).
If you want you image centred then you will need to know where this centre is. If you are centring about the drawing area alone then you can get this as (widget->allocation.width)/2,(widget->allocation.height)/2. If you want to centre it about the entire window you will need to know the dimensions of the main window as well as the coordinates of the origin of the canvas.

qwertyui · **Joined:** Sat Sep 03, 2011 6:36 pm **Posts:** 94

Thanks!Didnt know the drawing area was meant for that purpose... :)

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Drawing cairo with other widgets

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