The GtkDrawingArea widget is used for creating custom user interface
elements. It's essentially a blank widget; you can draw on
widget->window. 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
gtkWidgetAddEvents 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 "configure_event" signal to take any necessary actions
when the widget changes size.
- The "expose_event" 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.
expose_event_callback <- function(widget, event, data) {
gdkDrawArc(widget[["window"]],
widget[["style"]][["fgGc"]][[widget[["state"]]+1]],
TRUE, 0, 0, widget[["allocation"]]$width,
widget[["allocation"]]$height, 0, 64 * 360)
return(TRUE)
}
[...] drawing_area = gtkDrawingArea()
drawing_area$setSizeRequest(100, 100)
gSignalConnect(drawing_area, "expose_event", expose_event_callback)
Expose events are normally delivered when a drawing area first comes
onscreen, or when it's covered by another window and then uncovered
(exposed). You can also force an expose event by adding to the "damage
region" of the drawing area's window; gtkWidgetQueueDrawArea and
gdkWindowInvalidateRect are equally good ways to do this. You'll
then get an expose event for the invalid region. The available routines for drawing are documented on the GDK Drawing Primitives page.
See also gdkDrawPixbuf for drawing a GdkPixbuf. To receive mouse events on a drawing area, you will need to enable
them with gtkWidgetAddEvents. To receive keyboard events, you
will need to set the GTK_CAN_FOCUS flag on the drawing area, and
should probably draw some user-visible indication that the drawing
area is focused. Use the gtkHasFocus() function in your expose event
handler to decide whether to draw the focus indicator. See
gtkPaintFocus for one way to draw focus.