SPY++ style Window finder tool in VB.net

Public Class Form1
 
    Private prevHandle As IntPtr
    Private prevRC As Rect
 
    Public Structure PointAPI
 
        Public X As Integer
        Public Y As Integer
 
        Public Sub New(ByVal x As Integer, ByVal y As Integer)
            Me.X = x
            Me.Y = y
        End Sub
 
    End Structure
 
    Public Structure Rect
        Public Left As Integer
        Public Top As Integer
        Public Right As Integer
        Public Bottom As Integer
    End Structure
 
    Public Declare Function WindowFromPoint Lib "user32" (ByVal pt As PointAPI) As IntPtr
    Public Declare Function GetWindowRect Lib "user32" (ByVal handle As IntPtr, ByRef lpRect As Rect) As Integer
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        PictureBox1.BorderStyle = BorderStyle.FixedSingle
        PictureBox1.BackColor = Color.Red
        PictureBox1.Cursor = Cursors.Cross
    End Sub
 
    Private Sub Form1_Shown(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Shown
        MessageBox.Show("Drag the PictureBox around the screen...")
    End Sub
 
    Private Sub PictureBox1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseDown
        If e.Button = Windows.Forms.MouseButtons.Left Then
            prevHandle = IntPtr.Zero
        End If
    End Sub
 
    Private Sub PictureBox1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseMove
        If e.Button = Windows.Forms.MouseButtons.Left Then
            Dim pt As New PointAPI(Cursor.Position.X, Cursor.Position.Y)
            Dim handle As IntPtr = WindowFromPoint(pt)
 
            Label1.Text = handle.ToString("X")
 
            If Not handle.Equals(prevHandle) AndAlso Not prevHandle.Equals(IntPtr.Zero) Then
                ' erase previous rectanlge
                ControlPaint.DrawReversibleFrame(New Rectangle(prevRC.Left, prevRC.Top, prevRC.Right - prevRC.Left, prevRC.Bottom - prevRC.Top), Color.Black, FrameStyle.Thick)
            End If
 
            If Not handle.Equals(prevHandle) Then
                ' get new rectangle
                GetWindowRect(handle, prevRC)
 
                ' draw new rectangle
                ControlPaint.DrawReversibleFrame(New Rectangle(prevRC.Left, prevRC.Top, prevRC.Right - prevRC.Left, prevRC.Bottom - prevRC.Top), Color.Black, FrameStyle.Thick)
            End If
 
            ' store new handle
            prevHandle = handle
        End If
    End Sub
 
    Private Sub PictureBox1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseUp
        If e.Button = Windows.Forms.MouseButtons.Left Then
            ControlPaint.DrawReversibleFrame(New Rectangle(prevRC.Left, prevRC.Top, prevRC.Right - prevRC.Left, prevRC.Bottom - prevRC.Top), Color.Black, FrameStyle.Thick)
        End If
    End Sub
 
End Class

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