Make a Form's clicks "fall through" to the application below

Question

I've made a form with an opacity of 30%, and I want this to overlay on my screen so I can draw a grid on it whilst still being able to control any programs underneath. So I want the form I created with the grid to ignore my mouse events, so I can click through to the program underneath but still have it displaying on top.

Any ideas on this one?

Answer 1

You can specify Transparent Key Color to some color value of forms backcolor for clickthru area this color should be different from Grid Color you choose

This is VB.Net Code I tried should not be difficult to convert to C#

Private Sub frmTest_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
    Dim rc As Rectangle = New Rectangle(0, 0, Me.Width - 1, Me.Height - 1)
    Using br As New Drawing2D.HatchBrush(Drawing2D.HatchStyle.Cross, Color.Silver, Color.Transparent)
        e.Graphics.FillRectangle(br, rc)
    End Using
End Sub

Private Sub frmTest_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Me.TopMost = True : Me.Opacity = 10% : Me.WindowState = FormWindowState.Maximized
    Me.BackColor = Color.White
    Me.TransparencyKey = Color.White
    Me.FormBorderStyle = Windows.Forms.FormBorderStyle.None
End Sub