GI.Gtk.Objects.DrawingArea

The DrawingArea 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 widgetAddEvents 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 sizeAllocate 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 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 renderBackground in your draw method.

Simple GtkDrawingArea usage

C code

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; widgetQueueDrawArea and windowInvalidateRect 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 widgetAddEvents. 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 widgetHasFocus in your expose event handler to decide whether to draw the focus indicator. See renderFocus for one way to draw focus.

Exported types

newtype DrawingArea

Memory-managed wrapper type.

Constructors

DrawingArea (ManagedPtr DrawingArea)

Instances

Eq DrawingArea

Defined in GI.Gtk.Objects.DrawingArea

Methods

(==) :: DrawingArea -> DrawingArea -> Bool

(/=) :: DrawingArea -> DrawingArea -> Bool

IsGValue DrawingArea

Convert DrawingArea to and from GValue with toGValue and fromGValue.

Defined in GI.Gtk.Objects.DrawingArea

Methods

toGValue :: DrawingArea -> IO GValue

fromGValue :: GValue -> IO DrawingArea

GObject DrawingArea

Defined in GI.Gtk.Objects.DrawingArea

Methods

gobjectType :: IO GType

HasParentTypes DrawingArea

Defined in GI.Gtk.Objects.DrawingArea

type ParentTypes DrawingArea

Defined in GI.Gtk.Objects.DrawingArea

type ParentTypes DrawingArea = '[Widget, Object, ImplementorIface, Buildable]

class (GObject o, IsDescendantOf DrawingArea o) => IsDrawingArea o

Type class for types which can be safely cast to DrawingArea, for instance with toDrawingArea.

Instances

(GObject o, IsDescendantOf DrawingArea o) => IsDrawingArea o

Defined in GI.Gtk.Objects.DrawingArea

toDrawingArea :: (MonadIO m, IsDrawingArea o) => o -> m DrawingArea

Cast to DrawingArea, for types for which this is known to be safe. For general casts, use castTo.

noDrawingArea :: Maybe DrawingArea

A convenience alias for Nothing :: Maybe DrawingArea.

Methods

Overloaded methods

new

drawingAreaNew

Arguments

:: (HasCallStack, MonadIO m)

=> m DrawingArea

Returns: a new DrawingArea

Creates a new drawing area.