GtkDrawingArea

GtkDrawingArea — A simple widget for drawing with cairo

Properties

gint content-height Read / Write
gint content-width Read / Write

Signals

void resize Run Last

Types and Values

Object Hierarchy

    GObject
    ╰── GInitiallyUnowned
        ╰── GtkWidget
            ╰── GtkDrawingArea

Implemented Interfaces

GtkDrawingArea implements AtkImplementorIface, GtkBuildable and GtkConstraintTarget.

Includes

#include <gtk/gtk.h>

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:

  • 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 gtk_drawing_area_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

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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);
}

void 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);

}

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 gtk_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 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.

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

Functions

gtk_drawing_area_new ()

GtkWidget *
gtk_drawing_area_new (void);

Creates a new drawing area.

Returns

a new GtkDrawingArea


gtk_drawing_area_get_content_width ()

int
gtk_drawing_area_get_content_width (GtkDrawingArea *self);

Retrieves the value previously set via gtk_drawing_area_set_content_width().

Parameters

self

a GtkDrawingArea

 

Returns

The width requested for content of the drawing area


gtk_drawing_area_set_content_width ()

void
gtk_drawing_area_set_content_width (GtkDrawingArea *self,
                                    int width);

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 gtk_widget_set_halign() to avoid that.

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

Parameters

self

a GtkDrawingArea

 

width

the width of contents

 

gtk_drawing_area_get_content_height ()

int
gtk_drawing_area_get_content_height (GtkDrawingArea *self);

Retrieves the value previously set via gtk_drawing_area_set_content_height().

Parameters

self

a GtkDrawingArea

 

Returns

The height requested for content of the drawing area


gtk_drawing_area_set_content_height ()

void
gtk_drawing_area_set_content_height (GtkDrawingArea *self,
                                     int height);

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 gtk_widget_set_valign() to avoid that.

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

Parameters

self

a GtkDrawingArea

 

height

the height of contents

 

GtkDrawingAreaDrawFunc ()

void
(*GtkDrawingAreaDrawFunc) (GtkDrawingArea *drawing_area,
                           cairo_t *cr,
                           int width,
                           int height,
                           gpointer user_data);

Whenever drawing_area needs to redraw, this function will be called.

This function should exclusively redraw the contents of the drawing area and must not call any widget functions that cause changes.

Parameters

drawing_area

the GtkDrawingArea to redraw

 

cr

the context to draw to

 

width

the actual width of the contents. This value will be at least as wide as GtkDrawingArea:width.

 

height

the actual height of the contents. This value will be at least as wide as GtkDrawingArea:height.

 

user_data

user data.

[closure]

gtk_drawing_area_set_draw_func ()

void
gtk_drawing_area_set_draw_func (GtkDrawingArea *self,
                                GtkDrawingAreaDrawFunc draw_func,
                                gpointer user_data,
                                GDestroyNotify destroy);

Setting a draw function is the main thing you want to do when using a drawing area. It 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 gtk_widget_queue_draw() on the drawing area. This will cause a redraw and will call draw_func again.

Parameters

self

a GtkDrawingArea

 

draw_func

callback that lets you draw the drawing area's contents.

[allow-none]

user_data

user data passed to draw_func .

[closure]

destroy

destroy notifier for user_data

 

Types and Values

struct GtkDrawingArea

struct GtkDrawingArea;

Property Details

The “content-height” property

  “content-height”           gint

The content height. See gtk_drawing_area_set_content_height() for details.

Owner: GtkDrawingArea

Flags: Read / Write

Allowed values: >= 0

Default value: 0


The “content-width” property

  “content-width”            gint

The content width. See gtk_drawing_area_set_content_width() for details.

Owner: GtkDrawingArea

Flags: Read / Write

Allowed values: >= 0

Default value: 0

Signal Details

The “resize” signal

void
user_function (GtkDrawingArea *area,
               gint            width,
               gint            height,
               gpointer        user_data)

The ::resize signal is 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

area

the GtkDrawingArea that emitted the signal

 

width

the width of the viewport

 

height

the height of the viewport

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last

See Also

GtkImage