CtkDrawingArea: CTK+ 3 Reference Manual

## CtkDrawingArea CtkDrawingArea — A widget for custom user interface elements |

## Functions

CtkWidget * | ctk_drawing_area_new ()

## Types and Values

struct | CtkDrawingArea

## Object Hierarchy

        GObject
        ╰── GInitiallyUnowned
            ╰── CtkWidget
                ╰── CtkDrawingArea

## Implemented Interfaces

CtkDrawingArea implements AtkImplementorIface and CtkBuildable.

## Includes

    #include <ctk/ctk.h>

## Description

The CtkDrawingArea 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 `ctk_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 CDK 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 CDK 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 `ctk_render_background()` in your ::draw method.

#### Simple CtkDrawingArea usage

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    gboolean
    draw_callback (CtkWidget *widget, cairo_t *cr, gpointer data)
    {
      guint width, height;
      CdkRGBA color;
      CtkStyleContext *context;

      context = ctk_widget_get_style_context (widget);

      width = ctk_widget_get_allocated_width (widget);
      height = ctk_widget_get_allocated_height (widget);

      ctk_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);

      ctk_style_context_get_color (context,
                                   ctk_style_context_get_state (context),
                                   &color);
      cdk_cairo_set_source_rgba (cr, &color);

      cairo_fill (cr);

     return FALSE;
    }
    [...]
      CtkWidget *drawing_area = ctk_drawing_area_new ();
      ctk_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; `ctk_widget_queue_draw_area()` and `cdk_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 CDK Drawing Primitives page and the cairo documentation.

To receive mouse events on a drawing area, you will need to enable them with `ctk_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 `ctk_widget_has_focus()` in your expose event handler to decide whether to draw the focus indicator. See `ctk_render_focus()` for one way to draw focus.

## Functions

### ctk_drawing_area_new ()

    CtkWidget *
    ctk_drawing_area_new (void);

Creates a new drawing area.

#### Returns

a new CtkDrawingArea

## Types and Values

### struct CtkDrawingArea

    struct CtkDrawingArea;

## See Also

CtkImage