The Gtk.Drawing_Area.Gtk_Drawing_Area widget is used for creating custom user interface elements. It's 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
Gtk.Widget.Add_Events to enable events you wish to receive.)
The Gtk.Widget.Gtk_Widget::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 Gtk.Widget.Gtk_Widget::size-allocate signal to take any necessary
actions when the widget changes size.
The Gtk.Widget.Gtk_Widget::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 before sending the expose event, and that drawing is implicitly clipped to the exposed area. If you want to have a theme-provided background, you need to call Gtk.Style_Context.Render_Background in your ::draw method.
## Simple GtkDrawingArea usage
gboolean
draw_callback (GtkWidget *widget, cairo_t *cr, gpointer data)
{
guint width, height;
GdkRGBA color;
GtkStyleContext *context;
context = gtk_widget_get_style_context (widget);
width = gtk_widget_get_allocated_width (widget);
height = gtk_widget_get_allocated_height (widget);
gtk_render_background (context, cr, 0, 0, width, height);
cairo_arc (cr,
width / 2.0, height / 2.0,
MIN (width, height) / 2.0,
0, 2 * G_PI);
gtk_style_context_get_color (context,
gtk_style_context_get_state (context),
&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's 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; Gtk.Widget.Queue_Draw_Area and Gdk.Window.Invalidate_Rect are equally good ways to do this. You'll then get a draw signal for the invalid region.
The available routines for drawing are documented on the [GDK Drawing Primitives][gdk3-Cairo-Interaction] page and the cairo documentation.
To receive mouse events on a drawing area, you will need to enable them with Gtk.Widget.Add_Events. 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 Gtk.Widget.Has_Focus in your expose event handler to decide whether to draw the focus indicator. See Gtk.Style_Context.Render_Focus for one way to draw focus.
See also the Double_Buffer widget provided in the GtkAda examples for an advanced example that demonstrates how to use double buffering, to avoid flickering in your drawings.
<group>Drawing</group> <testgtk>libart_demo.adb</testgtk>
function "+"
(Widget : access Gtk_Drawing_Area_Record'Class)
return Gtk.Buildable.Gtk_Buildable
function "-"
(Interf : Gtk.Buildable.Gtk_Buildable)
return Gtk_Drawing_Area
function Get_Type return Glib.GType
type Gtk_Drawing_Area is access all Gtk_Drawing_Area_Record'Class;
function Gtk_Drawing_Area_New return Gtk_Drawing_Area
Creates a new drawing area.
type Gtk_Drawing_Area_Record is new Gtk_Widget_Record with null record;
procedure Gtk_New (Drawing_Area : out Gtk_Drawing_Area)
Creates a new drawing area. Initialize does nothing if the object was already created with another call to Initialize* or G_New.
package Implements_Gtk_Buildable is new Glib.Types.Implements
(Gtk.Buildable.Gtk_Buildable, Gtk_Drawing_Area_Record, Gtk_Drawing_Area);
procedure Initialize
(Drawing_Area : not null access Gtk_Drawing_Area_Record'Class)
Creates a new drawing area. Initialize does nothing if the object was already created with another call to Initialize* or G_New.