WinForm特效:桌面上的遮罩层

        using System;
        using System.Drawing;
        using System.Windows.Forms;
        using System.Runtime.InteropServices;
        namespace WindowsApplication40
        {
            public partial class Form1 : Form
            {
                public Form1()
                {
                    InitializeComponent();
                }
                [DllImport("user32.dll", EntryPoint = "GetWindowLong")]
                public static extern long GetWindowLong(IntPtr hwnd, int nIndex);
                [DllImport("user32.dll", EntryPoint = "SetWindowLong")]
                public static extern long SetWindowLong(IntPtr hwnd, int nIndex, long dwNewLong);
                [DllImport("user32", EntryPoint = "SetLayeredWindowAttributes")]
                private static extern int SetLayeredWindowAttributes(IntPtr Handle, int crKey, byte bAlpha, int dwFlags);
                const int GWL_EXSTYLE = -20;
                const int WS_EX_TRANSPARENT = 0x20;
                const int WS_EX_LAYERED = 0x80000;
                const int LWA_ALPHA = 2;
                private void Form1_Load(object sender, EventArgs e)
                {
                    this.BackColor = Color.Silver;
                    this.TopMost = true;
                    this.FormBorderStyle = FormBorderStyle.None;
                    this.WindowState = FormWindowState.Maximized;
                    SetWindowLong(Handle, GWL_EXSTYLE, GetWindowLong(Handle, GWL_EXSTYLE) | WS_EX_TRANSPARENT | WS_EX_LAYERED);
                    SetLayeredWindowAttributes(Handle, 0, 128, LWA_ALPHA );
                }
            }
        }