private void DrawWindows(GuiWindowCollection windows, float deltaSeconds)
 {
     foreach (var window in windows)
     {
         window.Draw(this, _renderer, deltaSeconds);
         DrawChildren(window.Controls, deltaSeconds);
     }
 }
 public GuiScreen(GuiSkin skin)
 {
     Skin     = skin;
     Controls = new GuiControlCollection {
         ItemAdded = c => _isLayoutRequired = true
     };
     Windows = new GuiWindowCollection(this)
     {
         ItemAdded = w => _isLayoutRequired = true
     };
 }