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Description
The GtkDrawingArea 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 “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 “size-allocate” 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.
Simple GtkDrawingArea usage
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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’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 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_render_focus() for one way to draw focus.