How to know if Graphic object is being displayed?

[c-s]

Kind of like this:

Code:

{curl 7.0, 8.0 applet}

{def frame = {Frame}}
{def child1 = {Frame "Child1"}}
{def child2 = {Frame "Child2"}}
{def td =
    {TextDisplay
        {on AttachEvent do
            {td.animate
                interval = 1s,
                {on TimerEvent do
                    {if child1.display-context == null then
                        set td.value = "not displayed"
                     else
                        {if-non-null v = {child1.get-view} then
                            {switch v.visibility
                             case "minimized", "hidden" do
                                set td.value = "not displayed"
                             else
                                set td.value = "displayed"
                                {dump {DateTime}, "displayed!"}
                            }
                         else
                            set td.value = "not displayed"
                        }
                    }
                }
            }
        }
    }
}

{VBox
    frame,
    {HBox
        {CommandButton
            label="show child1",
            {on Action do
                {frame.add child1, replace?=true}
            }
        },
        {CommandButton
            label="show child2",
            {on Action do
                {frame.add child2, replace?=true}
            }
        }
    },
    td
}

Note that if you minimize the browser window, the console will stop showing the displayed message.