DrawingArea

class DrawingArea(**properties: Any)

Superclasses: Widget, InitiallyUnowned, Object

Implemented Interfaces: Accessible, Buildable, ConstraintTarget

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 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 resize signal to take any necessary actions when the widget changes size.

• Call 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;

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

  gtk_widget_get_color (GTK_WIDGET (area),
                        &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 queue_draw. This will cause the drawing area to call the draw function again.

The available routines for drawing are documented in the Cairo documentation; GDK offers additional API to integrate with Cairo, like cairo_set_source_rgba or cairo_set_source_pixbuf.

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.

Constructors

class DrawingArea

classmethod new() → Widget

Creates a new drawing area.

Methods

class DrawingArea

get_content_height() → int

Retrieves the content height of the GtkDrawingArea.

get_content_width() → int

Retrieves the content width of the GtkDrawingArea.

set_content_height(height: int) → None

Sets the desired height of the contents of the drawing area.

Note that because widgets may be allocated larger sizes than they requested, it is possible that the actual height passed to your draw function is larger than the height set here. You can use set_valign to avoid that.

If the height is set to 0 (the default), the drawing area may disappear.

Parameters:

height – the height of contents

set_content_width(width: int) → None

Sets the desired width of the contents of the drawing area.

Note that because widgets may be allocated larger sizes than they requested, it is possible that the actual width passed to your draw function is larger than the width set here. You can use set_halign to avoid that.

If the width is set to 0 (the default), the drawing area may disappear.

Parameters:

width – the width of contents

set_draw_func(draw_func: Callable[[...], None] | None = None, *user_data: Any) → None

Setting a draw function is the main thing you want to do when using a drawing area.

The draw function is called whenever GTK needs to draw the contents of the drawing area to the screen.

The draw function will be called during the drawing stage of GTK. In the drawing stage it is not allowed to change properties of any GTK widgets or call any functions that would cause any properties to be changed. You should restrict yourself exclusively to drawing your contents in the draw function.

If what you are drawing does change, call queue_draw on the drawing area. This will cause a redraw and will call draw_func again.

Parameters:

• draw_func – callback that lets you draw the drawing area’s contents

• user_data – user data passed to draw_func

Properties

class DrawingArea

props.content_height: int

The content height.

props.content_width: int

The content width.

Signals

class DrawingArea.signals

resize(width: int, height: int) → None

Emitted once when the widget is realized, and then each time the widget is changed while realized.

This is useful in order to keep state up to date with the widget size, like for instance a backing surface.

Parameters:

• width – the width of the viewport

• height – the height of the viewport

Virtual Methods

class DrawingArea

do_resize(width: int, height: int) → None

Parameters:

• width

• height

Fields

class DrawingArea

widget