function BeginWindows () : void

Description

Mark the beginning area of all popup windows.

GUI.Window behaves somewhat differently in the editor than inside your games. In games, GUI.Window pops up a window on your screen. In the editor, GUI.Window shows a subwindow inside one of your editor windows. Begin/EndWindows is used to determine where these can go. You need to have all calls to GUI.Window or GUILayout.Window inside a BeginWindows / EndWindows pair. Like this:

Simple editor Window with a window and a button inside.

    class GUIWindowDemo extends EditorWindow {
        // The position of the window
        var windowRect = Rect (100,100,200,200);
        // Main GUI Function
        function OnGUI () {
            // Begin Window
            BeginWindows ();
            
            // All GUI.Window or GUILayout.Window must come inside here
            windowRect = GUILayout.Window (1, windowRect, DoWindow, "Hi There");        
            
            // Collect all the windows between the two.
            EndWindows ();            
        }
        
        // The window function. This works just like ingame GUI.Window
        function DoWindow () {
            GUILayout.Button ("Hi");
            GUI.DragWindow ();        
        }
        
        // Add menu item to show this demo.
        @MenuItem ("Test/GUIWindow Demo")
        static function Init () {
            EditorWindow.GetWindow (GUIWindowDemo);
        }
    }

The placement of the BeginWindows / EndWindows pair determines where popup windows will appear; all windows are clipped to the clipping area defined by GUI.BeginGroup or GUI.BeginScrollview. A small example of that

Simple editor window with a window and a button inside using scroll bars.

    class GUIWindowDemo2 extends EditorWindow {
        // The position of the window
        var windowRect = Rect (100,100,200,200);
        // Scroll position
        var scrollPos = Vector2.zero;
        function OnGUI () {
            // Set up a scroll view
            scrollPos = GUI.BeginScrollView (
                new Rect (0, 0, position.width, position.height), 
                scrollPos, 
                new Rect (0, 0, 1000, 1000)
            );
            // Same code as before - make a window. Only now, it's INSIDE the scrollview
            BeginWindows ();    
            windowRect = GUILayout.Window (1, windowRect, DoWindow, "Hi There");                
            EndWindows ();
            
            // Close the scroll view
            GUI.EndScrollView ();
        }
        
        function DoWindow () {
            GUILayout.Button ("Hi");
            GUI.DragWindow ();        
        }
        @MenuItem ("Test/GUIWindow Demo 2")
        static function Init () {
            EditorWindow.GetWindow (GUIWindowDemo2);
        }
    }