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


// http://stackoverflow.com/questions/479284/mouse-wheel-event-c


namespace UserControls
{
    public class ChildMouseWheelManagedForm : Form, IMessageFilter
    {
        private bool managed;
        public ChildMouseWheelManagedForm()
            : this(true)
        {
        }

        public ChildMouseWheelManagedForm(bool start)
        {
            managed = false;
            if (start)
                ManagedMouseWheelStart();
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing)
                ManagedMouseWheelStop();
            base.Dispose(disposing);
        }

        /************************************
         * IMessageFilter implementation
         * *********************************/
        private const int WM_MOUSEWHEEL = 0x20a;
        // P/Invoke declarations
        [DllImport("user32.dll")]
        private static extern IntPtr WindowFromPoint(Point pt);
        [DllImport("user32.dll")]
        private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);

        private bool IsChild(Control ctrl)
        {
            Control loopCtrl = ctrl;

            while (loopCtrl != null && loopCtrl != this)
                 loopCtrl = loopCtrl.Parent;

            return (loopCtrl == this);
        }

        public bool PreFilterMessage(ref Message m)
        {
            if (m.Msg == WM_MOUSEWHEEL)
            {
                //Ensure the message was sent to a child of the current form
                if (IsChild(Control.FromHandle(m.HWnd)))
                //if (this.Contains(Control.FromHandle(m.HWnd)))
                {
                    // Find the control at screen position m.LParam
                    Point pos = new Point(m.LParam.ToInt32() & 0xffff, m.LParam.ToInt32() >> 16);

                    // Is mouse inside the form
                    if (pos.X >= this.Left && pos.X <= Left + Width && pos.Y >= Top && pos.Y <= Top+Height)
                    {
                        //Ensure control under the mouse is valid and is not the target control
                        //otherwise we'd be trap in a loop.
                        IntPtr hWnd = WindowFromPoint(pos);
                        if (hWnd != IntPtr.Zero && hWnd != m.HWnd && Control.FromHandle(hWnd) != null)
                        {
                            SendMessage(hWnd, m.Msg, m.WParam, m.LParam);
                            return true;
                        }
                    }
                }
            }
            return false;
        }

        /****************************************
         * MouseWheelManagedForm specific methods
         * **************************************/
        public void ManagedMouseWheelStart()
        {
            if (!managed)
            {
                managed = true;
                Application.AddMessageFilter(this);
            }
        }

        public void ManagedMouseWheelStop()
        {
            if (managed)
            {
                managed = false;
                Application.RemoveMessageFilter(this);
            }
        }

    }
}