C#

[STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
      <code>MessageFilter filter = new MessageFilter();
            Application.AddMessageFilter(filter);</code>
            Application.Run(new Form());
        }
        <code>
        class MessageFilter:IMessageFilter</code>
        {
            private const int WM_NCLBUTTONUP = 0xA2;
            private const int WM_NCLBUTTONDOWN = 0xA1;

            public bool PreFilterMessage(ref Message m)
            {
          <code>//When the mouse is pressed(m.Msg == WM_NCLBUTTONDOWN)
                //on the nonClientArea and on the
                //minimize button(m.WParam == (IntPtr)0x8)</code>
                if (m.Msg == WM_NCLBUTTONDOWN && m.WParam == (IntPtr)0x8)
                {
                     //Raise some events
               <code>//Because it returns true,
                     //the message will not be sent to the window!
                     return true;
                     //if it returns false,
                     //the WM_NCLBUTTONUP would not be sent
                     //to the window!</code>
                }
          <code>//When the mouse is released(m.Msg == WM_NCLBUTTONUP)
                //on the nonClientArea and on the
                //minimize button(m.WParam == (IntPtr)0x8)</code>
                else if (m.Msg == WM_NCLBUTTONUP && m.WParam == (IntPtr)0x8)
                {
                    //Raise some events
                    return false;
                }
                return false;
            }
        }

Sojaner wrote:

if I return true for the if (m.Msg == WM_NCLBUTTONDOWN && m.WParam == (IntPtr)0x8), the press message would be ignored and would not be sent to the window and so the Capture would not start!

Sojaner wrote:

But that way I should ignore the press message and so the window would not be minimized!

Sojaner wrote:

Now, did you get my problem?

Regards

private const int WM_NCLBUTTONDOWN = 0xA1;
private const int WM_NCLBUTTONUP = 0xA2;
        
bool filterOff = true;
Message message = new Message();
bool internalMessage = false;

        [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
        protected override void WndProc(ref Message m)
        {
            if (m.Msg == WM_NCLBUTTONDOWN && m.WParam == (IntPtr)0x8)
            {
                if (internalMessage)
                {
                    internalMessage = false;
                }
                else
                {
                    message = m;
                    if (filterOff)
                    {
                        Message mes = new Message();
                        mes.HWnd = this.Handle;
                        mes.Msg = 162;
                        mes.WParam = m.WParam;
                        mes.LParam = IntPtr.Zero;
                        this.WndProc(ref mes);
                    }
                    return;
                }

            }
            else if (m.Msg == WM_NCLBUTTONUP && m.WParam == (IntPtr)0x8)
            {
                internalMessage = true;
                this.WndProc(ref message);
                return;
            }
            base.WndProc(ref m);
        }

        private void Form_KeyUp(object sender, KeyEventArgs e)
        {
            if(e.KeyCode.ToString() == "Escape")
            {
                if (!filterOff) { filterOff = true; }
                else
                {
                    filterOff = false;
                }
                
            }
        }