Gtk / Gtk4: transperent window (overlay) with layers

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Hi! I want to make transparent window with several graphic layers and information.

I found ‘opacity’ property, but it work with window and child canvas.

So, I found partial solution:

c = @GtkCanvas()
win = GtkWindow(c, "Canvas")

ccall((:gtk_window_set_keep_above, Gtk.libgtk), Nothing, (Ptr{GObject},), win)
ccall((:gtk_widget_set_app_paintable, Gtk.libgtk), Nothing, (Ptr{GObject}, Bool), win, true)
show(c)

@guarded draw(c) do widget
  ctx = getgc(c)
  h = height(c)
  w = width(c)

  rectangle(ctx,10, 100, w/2, h/2)
  set_source_rgb(ctx, 0, 1, 0)

  fill(ctx)

end

@guarded draw(c) do widget
  ctx = getgc(c)
  h = height(c)
  w = width(c)

  rectangle(ctx, 0, 0, w/4, h/4)
  set_source_rgb(ctx, 1,0,0)
  fill(ctx)

  rectangle(ctx,10, 100, w/2, h/2)
  set_source_rgb(ctx, 0, 1, 0)

  fill(ctx)
end

signal_connect(win,"key_press_event") do widget, event
  if event.keyval == 32
    @guarded draw(c) do widget2
      ctx = getgc(c)
      fill(ctx)
    end
  end
  show(c)
  println(event.keyval)
end

But It clear only if windows resized. What is a good way to make some moving objects in canvas?