[Gtk-sharp-list] Gdk XOR Drawing Problem

[Manuel Alejandro Cerón Estrada]

Hello,

I am trying to implement a rubber band for my drawing application in
Gtk#. I want to make use of the Gdk XOR drawing for this purpose. But,
for some reason, it does not work appropriately. I have this simple
code:

using System;
using Gtk;
using Gdk;

public class MyDrawingArea: Gtk.DrawingArea {
	public MyDrawingArea()
	{
		SetSizeRequest (500, 500);
		AddEvents ((int)Gdk.EventMask.AllEventsMask);
	}
	
	protected override bool OnButtonPressEvent (EventButton ev)
	{
		Gdk.GC gc = new Gdk.GC(ev.Window);
		gc.Function = Gdk.Function.Xor;
		ev.Window.DrawRectangle(gc, true, 100, 100, 200, 200);
		return true;
	}

}

public class MyWindow: Gtk.Window {
	public MyWindow(): base("My Window")
	{
		MyDrawingArea area = new MyDrawingArea();
		Add(area);
		ShowAll();
	}
	
	public static void Main()
	{
		Application.Init();
		new MyWindow();
		Application.Run();
	}
	
}

When I assign the XOR function to the Gdk GC, I would expect that the
first time I click on the Drawing Area, a rectangle should be drawn,
the second time, the rectangle should be erased. The problem is that,
once I set Xor as the function, the rectangle it is never draw. Other
functions like Invert works fine, but Xor does not seem to work at
all. Is there a problem with my code?

In advance, thank you. And please excuse my bad english

Manuel Alejandro Cerón Estrada