Extend a Panel In Only One Direction

// Create a panel with a button that will extend the panel size in only one direction (downward in this case).
// The extension is also set at a pre-defined size.
// Features inside the initially hidden extension range can be shown or hidden again using the XtendD button.
 
Static Constant normaldepth = 80
Static Constant xtendeddepth = 170
 
Function SamplePanel()
 
    NewPanel/W=(10,25,255,25+normaldepth)/N=XtendablePanel/K=1 as "Xtend Me"
    ModifyPanel noEdit=1, fixedsize=1
        Button XtendD,pos={4,55},size={15,20},proc=XtendDown,title=">", userData="closed"
    SetDrawLayer UserBack
    DrawLine 22,65,242,65
    CheckBox acheckbox,pos={24,85},size={48,14},title="A Box"
    return 0
end
 
Function XtendDown(ba) : ButtonControl
    STRUCT WMButtonAction &ba
    
    switch( ba.eventCode )
        case 2: // mouse up
            GetWindow kwTopWin wsize
            strswitch(ba.userData)
                case "closed":
                    Button XtendD title="v", userData="opened"
                    MoveWindow V_left,V_top,V_right,V_top+(xtendeddepth*72/ScreenResolution)
                    break
                case "opened":
                    Button XtendD title=">", userData="closed"
                    MoveWindow V_left,V_top,V_right,V_top+(normaldepth*72/ScreenResolution)
                    break
            endswitch
            break
    endswitch
    return 0
end