Package: gtk

Class gtk-drawing-area

Superclasses

gtk-widget, g-initially-unowned, gtk-buildable, g-object, common-lisp:standard-object, common-lisp:t

Documented Subclasses

None

Direct Slots

None

Details

The gtk-drawing-area widget is used for creating custom user interface elements. It is essentially a blank widget; you can draw on it. After creating a drawing area, the application may want to connect to:
  • Mouse and button press signals to respond to input from the user. Use the gtk-widget-add-events function to enable events you wish to receive.
  • The "realize" signal to take any necessary actions when the widget is instantiated on a particular display. Create GDK resources in response to this signal.
  • The "configure-event" signal to take any necessary actions when the widget changes size.
  • The "draw" signal to handle redrawing the contents of the widget.
The following code portion demonstrates using a drawing area to display a circle in the normal widget foreground color.

Note that GDK automatically clears the exposed area to the background color before sending the expose event, and that drawing is implicitly clipped to the exposed area.

Example: Simple gtk-drawing-area usage
 gboolean
 draw_callback (GtkWidget *widget, cairo_t *cr, gpointer data)
   {
     guint width, height;
     GdkRGBA color;

width = gtk_widget_get_allocated_width (widget); height = gtk_widget_get_allocated_height (widget); cairo_arc (cr, width / 2.0, height / 2.0, MIN (width, height) / 2.0, 0, 2 * G_PI);

gtk_style_context_get_color (gtk_widget_get_style_context (widget), 0, &color); gdk_cairo_set_source_rgba (cr, &color);

cairo_fill (cr);

return FALSE; } [...] GtkWidget *drawing_area = gtk_drawing_area_new (); gtk_widget_set_size_request (drawing_area, 100, 100); g_signal_connect (G_OBJECT (drawing_area), "draw", G_CALLBACK (draw_callback), NULL);
Draw signals are normally delivered when a drawing area first comes onscreen, or when it is covered by another window and then uncovered. You can also force an expose event by adding to the "damage region" of the drawing area's window; the gtk-widget-queue-draw-area and gdk-window-invalidate-rect functions are equally good ways to do this. You will then get a draw signal for the invalid region.

The available routines for drawing are documented on the GDK Drawing Primitives page and the cairo documentation.

To receive mouse events on a drawing area, you will need to enable them with the gtk-widget-add-events function. To receive keyboard events, you will need to set the can-focus property on the drawing area, and you should probably draw some user-visible indication that the drawing area is focused. Use the gtk-widget-has-focus function in your expose event handler to decide whether to draw the focus indicator. See the function for one way to draw focus.
 

Inherited Slot Access Functions

See also

2013-7-1