Tracking whether mouse pointer is inside a rectangle with .NET Rx.

RxMouseTracking.cs

private void Form1_Load(object sender, EventArgs e)
{
    // get an observable for mouse move event
    var mouseMove = Observable.FromEventPattern<MouseEventHandler, MouseEventArgs>(
        x => this.MouseMove += x, x => this.MouseMove -= x);
    
    // our rectangle
    var rect = new Rectangle(50, 50, 50, 50);

    // create event stream transformation
    mouseMove
        .Select(ea => rect.Contains(ea.EventArgs.X, ea.EventArgs.Y))
        .DistinctUntilChanged()
        .Select(x => x ? "Inside!" : "Outside")
        .Subscribe(x => MessageBox.Show(x));
}