A toplevel to manage offscreen rendering of child widgets

Description

GtkOffscreenWindow is strictly intended to be used for obtaining snapshots of widgets that are not part of a normal widget hierarchy. Since Gnome::Gtk3::OffscreenWindow is a toplevel widget you cannot obtain snapshots of a full window with it since you cannot pack a toplevel widget in another toplevel.

The idea is to take a widget and manually set the state of it, add it to a GtkOffscreenWindow and then retrieve the snapshot as a cairo-surface-t or Gnome::Gtk3::Pixbuf.

GtkOffscreenWindow derives from Gnome::Gtk3::Window only as an implementation detail. Applications should not use any API specific to Gnome::Gtk3::Window to operate on this object. It should be treated as a Gnome::Gtk3::Bin that has no parent widget.

When contained offscreen widgets are redrawn, GtkOffscreenWindow will emit a damage-event signal.

Synopsis

Declaration

unit class Gnome::Gtk3::OffscreenWindow;
also is Gnome::Gtk3::Window;

Uml Diagram

Example

An example where a grid with two buttons are rendered and saved in a png and a jpg image file.

# Setup something to show in an image.
my Gnome::Gtk3::Button $b1 .= new(:label<Stop>);
my Gnome::Gtk3::Button $b2 .= new(:label<Start>);
my Gnome::Gtk3::Grid $g  .= new;
$g.attach( $b1, 0, 0, 1, 1);
$g.attach( $b2, 1, 0, 1, 1);
$ow.add($g);
$ow.show-all;

# Must process pending events, otherwise nothing is shown! Note,
# that this is written outside the main event loop in the test program!
# Otherwise, this is not necessary.
my Gnome::Gtk3::Main $main .= new;
while $main.gtk-events-pending() { $main.iteration-do(False); }

# Now we can try to get the contents of the widget. First using
# a cairo_surface
my Gnome::Cairo::ImageSurface $image-surface .= new(
  :native-object($ow.get-surface)
);
$image-surface.write_to_png("OffscreenWindow-surface.png");
$image-surface.clear-object;

# Then using a pixbuf
my Gnome::Gdk3::Pixbuf $pb = $ow.get-pixbuf-rk;
my Gnome::Glib::Error $e = $pb.savev(
  "OffscreenWindow-pixbuf.jpg", 'jpeg', ['quality'], ['100']
);

The result of the png and jpg file;

Methods

new

This widget can only be created by calling new() without any options. Importing from other widgets using :native-object is not very useful. The glade GUI designer program has the offscreen window widget which can be placed in your design so the :build-id is still possible.

default, no options

Creates a toplevel container widget that is used to retrieve snapshots of widgets without showing them on the screen.

multi method new ( )

:build-id

Create a OffscreenWindow object using a native object returned from a builder. See also Gnome::GObject::Object.

multi method new ( Str :$build-id! )

get-pixbuf, get-pixbuf-rk

Retrieves a snapshot of the contained widget in the form of a Gnome::Gdk3::Pixbuf. This is a new pixbuf with a reference count of 1, and the application should unreference it once it is no longer needed.

method get-pixbuf ( --> N-GObject )
method get-pixbuf-rk ( --> Gnome::Gdk3::Pixbuf )

get-surface, get-surface-rk

Retrieves a snapshot of the contained widget in the form of a cairo-surface-t. If you need to keep this around over window resizes then you should add a reference to it.

Returns: A cairo-surface-t pointer to the offscreen surface, or undefined.

method get-surface ( --> cairo_surface_t )
method get-surface-rk ( --> Gnome::Cairo::Surface )

_gtk_offscreen_window_new

Creates a toplevel container widget that is used to retrieve snapshots of widgets without showing them on the screen.

Returns: A pointer to a Gnome::Gtk3::Widget

method _gtk_offscreen_window_new ( --> N-GObject )