Overlay semi-transparent images on Windows Forms

This article aims to provide a solution for overlaying a semi-transparent image on a Windows Form containing other controls, ensuring that the controls remain visible but inaccessible.

To achieve this effect, we will use another form and place it on top of the existing form. The new form's Opacity property controls the transparency level. Here is a custom class that can be added to your project:

using System;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.InteropServices;

public class Plexiglass : Form
{
    public Plexiglass(Form tocover)
    {
        // 自定義疊加窗體的外觀和行為
        this.BackColor = Color.DarkGray;
        this.Opacity = 0.30;
        this.FormBorderStyle = FormBorderStyle.None;
        this.ControlBox = false;
        this.ShowInTaskbar = false;
        this.StartPosition = FormStartPosition.Manual;
        this.AutoScaleMode = AutoScaleMode.None;
        this.Location = tocover.PointToScreen(Point.Empty);
        this.ClientSize = tocover.ClientSize;

        // 將疊加層與目標(biāo)窗體關(guān)聯(lián)，以跟蹤其移動(dòng)和大小調(diào)整事件
        tocover.LocationChanged += Cover_LocationChanged;
        tocover.ClientSizeChanged += Cover_ClientSizeChanged;
        this.Show(tocover);
        tocover.Focus();

        // 禁用Aero過(guò)渡效果，以獲得更流暢的效果
        if (Environment.OSVersion.Version.Major >= 6)
        {
            int value = 1;
            DwmSetWindowAttribute(tocover.Handle, DWMWA_TRANSITIONS_FORCEDISABLED, ref value, 4);
        }
    }

    // 事件處理程序，用于更新疊加層的位置和大小
    private void Cover_LocationChanged(object sender, EventArgs e)
    {
        this.Location = this.Owner.PointToScreen(Point.Empty);
    }
    private void Cover_ClientSizeChanged(object sender, EventArgs e)
    {
        this.ClientSize = this.Owner.ClientSize;
    }

    // 調(diào)整窗體行為，以確保目標(biāo)窗體保持焦點(diǎn)
    protected override void OnActivated(EventArgs e)
    {
        this.BeginInvoke(new Action(() => this.Owner.Activate()));
    }
    protected override void OnFormClosing(FormClosingEventArgs e)
    {
        this.Owner.LocationChanged -= Cover_LocationChanged;
        this.Owner.ClientSizeChanged -= Cover_ClientSizeChanged;
        if (!this.Owner.IsDisposed && Environment.OSVersion.Version.Major >= 6)
        {
            int value = 1;
            DwmSetWindowAttribute(this.Owner.Handle, DWMWA_TRANSITIONS_FORCEDISABLED, ref value, 4);
        }
        base.OnFormClosing(e);
    }

    // DWM API調(diào)用的常量
    private const int DWMWA_TRANSITIONS_FORCEDISABLED = 3;
    [DllImport("dwmapi.dll")]
    private static extern int DwmSetWindowAttribute(IntPtr hWnd, int attr, ref int value, int attrLen);
}

To overlay an image, create an instance of the Plexiglass class and pass the target form as a parameter when the form is displayed. This creates a semi-transparent overlay that covers the entire target form, allowing you to see existing controls but preventing interaction with them.

To remove the overlay, simply call the Plexiglass method of the form instance. Close()

The above is the detailed content of How to Create a Semi-Transparent Overlay on a Windows Form Using C#?. For more information, please follow other related articles on the PHP Chinese website!