Windows Forms: Pass clicks through a partially transparent always-on-top window

Question

I am designing a window that is always on screen and around 20% opaque. It is designed to be a sort of status window, so it is always on top, but I want people to be able to click through the window to any other application below. Here's the opaque window sitting on top of this SO post as I type right now:

See that grey bar? It would prevent me from typing in the tags box at the moment.

Do you have any evidence to back up that answer? I find that hard to believe... — Sam Weaver, Oct 04 '16 at 15:04
Believe it. My "evidence" is over a decade of experience using win forms. — rory.ap, Oct 04 '16 at 15:05
@rory.ap I think the posted answer is what the OP is looking for. Am I missing some part of the question? It's working on Windows 7. — Reza Aghaei, Oct 04 '16 at 15:19

Reza Aghaei · Accepted Answer · 2019-09-30T15:44:48.517

34

You can make a window, click-through by adding WS_EX_LAYERED and WS_EX_TRANSPARENT styles to its extended styles. Also to make it always on top set its TopMost to true and to make it semi-transparent use suitable Opacity value:

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        this.Opacity = 0.5;
        this.TopMost = true;
    }
    [DllImport("user32.dll", SetLastError = true)]
    static extern int GetWindowLong(IntPtr hWnd, int nIndex);
    [DllImport("user32.dll")]
    static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);
    const int GWL_EXSTYLE = -20;
    const int WS_EX_LAYERED = 0x80000;
    const int WS_EX_TRANSPARENT = 0x20;
    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);
        var style = GetWindowLong(this.Handle, GWL_EXSTYLE);
        SetWindowLong(this.Handle,GWL_EXSTYLE , style | WS_EX_LAYERED | WS_EX_TRANSPARENT);
    }
}

Sample Result

edited Sep 30 '19 at 15:44

answered Oct 04 '16 at 15:18

Reza Aghaei

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You could just override CreateParams and set the ExStyle instead using P/Invoke. – TnTinMn Oct 05 '16 at 01:42
I tried this solution but when I click through the window happens nothing – BruceOverflow Apr 03 '20 at 15:09
@BruceStackOverFlow Click will pass to the background window. – Reza Aghaei Apr 04 '20 at 04:08
I use ubuntu with mono seems that this not working... https://stackoverflow.com/questions/61000080/create-windows-transparent-without-interaction-with-mouse-and-keyboard-like-peek – BruceOverflow Apr 04 '20 at 11:10
@BruceStackOverFlow It's WinForms (.NET) on Windows not mono on Linux. – Reza Aghaei Apr 04 '20 at 11:46
Ya but mono support completely windows form 2.0, this work in part, for example, like as the posted gif but the click non work.... – BruceOverflow Apr 04 '20 at 11:55
@BruceStackOverFlow The part which is not working is in fact the Windows API part :) – Reza Aghaei Apr 04 '20 at 14:18

Windows Forms: Pass clicks through a partially transparent always-on-top window

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