Add option to hide GUI in Game Viewport

Source/Editor/Windows/GameWindow.cs

@@ -38,7 +38,7 @@ namespace FlaxEditor.Windows
                     _showGUI = value;
 
                     // Update root if it's in game
-                    if (Editor.StateMachine.IsPlayMode)
+                    //if (Editor.StateMachine.IsPlayMode)
                         _guiRoot.Visible = value;
                 }
             }
@@ -278,6 +278,18 @@ namespace FlaxEditor.Windows
                 takeScreenshot.Clicked += TakeScreenshot;
             }
 
+            menu.AddSeparator();
+
+            // Show GUI
+            {
+                var showGui = menu.AddButton("Show GUI");
+                var showGuiCheckbox = new CheckBox(140, 2, ShowGUI)
+                {
+                    Parent = showGui
+                };
+                showGuiCheckbox.StateChanged += x => ShowGUI = x.Checked;
+            }
+
             menu.MinimumWidth = 200;
             menu.AddSeparator();
         }