DrawingAreaRef

public struct DrawingAreaRef : DrawingAreaProtocol, GWeakCapturing

GtkDrawingArea is a widget that allows drawing with cairo.

It’s essentially a blank widget; you can draw on it. After creating a drawing area, the application may want to connect to:

• The [signalGtk.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 [signalGtk.DrawingArea::resize] signal to take any necessary actions when the widget changes size.

• Call [methodGtk.DrawingArea.set_draw_func] 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.

Simple GtkDrawingArea usage

static void
draw_function (GtkDrawingArea *area,
               cairo_t        *cr,
               int             width,
               int             height,
               gpointer        data)
{
  GdkRGBA color;
  GtkStyleContext *context;

  context = gtk_widget_get_style_context (GTK_WIDGET (area));

  cairo_arc (cr,
             width / 2.0, height / 2.0,
             MIN (width, height) / 2.0,
             0, 2 * G_PI);

  gtk_style_context_get_color (context,
                               &color);
  gdk_cairo_set_source_rgba (cr, &color);

  cairo_fill (cr);
}

int
main (int argc, char **argv)
{
  gtk_init ();

  GtkWidget *area = gtk_drawing_area_new ();
  gtk_drawing_area_set_content_width (GTK_DRAWING_AREA (area), 100);
  gtk_drawing_area_set_content_height (GTK_DRAWING_AREA (area), 100);
  gtk_drawing_area_set_draw_func (GTK_DRAWING_AREA (area),
                                  draw_function,
                                  NULL, NULL);
  return 0;
}

The draw function is normally called when a drawing area first comes onscreen, or when it’s covered by another window and then uncovered. You can also force a redraw by adding to the “damage region” of the drawing area’s window using [methodGtk.Widget.queue_draw]. This will cause the drawing area to call the draw function again.

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 use event controllers. 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.

If you need more complex control over your widget, you should consider creating your own GtkWidget subclass.

The DrawingAreaRef type acts as a lightweight Swift reference to an underlying GtkDrawingArea instance. It exposes methods that can operate on this data type through DrawingAreaProtocol conformance. Use DrawingAreaRef only as an unowned reference to an existing GtkDrawingArea instance.