C# WinForms Application Full Integration with HTMLHelp ( .chm ) - Help Topics, Context Sensitive Help, and Tooltips

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


namespace WinHelpLib
{


    /// <summary>
    /*
        TableOfContents - opens table of contents tab only - keyword is unused
        Topic - opens a topic in the current tab - keyword is the path to the topic
        TopicId - opens a topic in the current tab - keyword is the id (numeric only) of the topic in the [MAP] section (.h file)
        Index - opens the index tab - keyword fils the edit and selects accordingsly in the list below withouth chaning the displayed topic 
        Find - opens the find tab - keyword is unused
        AssociateIndex - does not seem to work properly 
        KeywordIndex - opens a topic in the current tab (sometimes changes to index tab) - keyword (sometimes changes the textbox and list index in index tab) changes the displayed topic to the selected one 
    */
    /// </summary>


    class HTMLHelpEx
    {

        const int HH_DISPLAY_TEXT_POPUP = 0x000E;

        [StructLayout(LayoutKind.Sequential)]
        struct Point
        {
            public Int32 x;
            public Int32 y;
        };

        [StructLayout(LayoutKind.Sequential)]
        struct Rect
        {
            public Int32 left;
            public Int32 top;
            public Int32 right;
            public Int32 bottom;
        };


        [StructLayout(LayoutKind.Sequential)]
        struct HH_POPUP
        {
            public Int32 cbStruct;
            public IntPtr hinst;              //4 bytes on x86, 8 on x64
            public UInt32 idString;
            [MarshalAs(UnmanagedType.LPWStr)] //Unicode
            public String pszText;
            public Point pt;
            public UInt32 clrForeground;
            public UInt32 clrBackground;
            public Rect rcMargins;
            [MarshalAs(UnmanagedType.LPWStr)] //Unicode
            public String pszFont;
        };


        [DllImport("hhctrl.ocx", CharSet = CharSet.Unicode, EntryPoint = "HtmlHelpW")]
        static extern IntPtr HtmlHelp(
           IntPtr caller,   //4 bytes on x86, 8 on x64
           String file,
           uint command,
           IntPtr data      //4 bytes on x86, 8 on x64
        );


        string sHelpFileName;
        string sCSStreamName;

        public HTMLHelpEx(string sName,string sCSName)
        {
            sHelpFileName = sName;
            sCSStreamName = sCSName;
        }

        public void ShowHelp(Control ctrl, HelpNavigator hn, object oKeyword)
        {
            Help.ShowHelp(ctrl, sHelpFileName, hn, oKeyword);
        }


        public void ShowContextHelp(uint idString, Control ctrl)
        {
            HH_POPUP sPUp = new HH_POPUP();

            sPUp.cbStruct = Marshal.SizeOf(sPUp);
            sPUp.hinst = IntPtr.Zero;
            sPUp.idString = idString;
            sPUp.pszText = String.Empty;
            sPUp.pt = new Point()
            {
                x = ctrl.PointToScreen(new System.Drawing.Point()).X,
                y = ctrl.PointToScreen(new System.Drawing.Point()).Y
            };
            sPUp.clrForeground = 0;
            sPUp.clrBackground = 0;
            sPUp.rcMargins = new Rect()
            {
                left = 10,
                top = 10,
                right = 10,
                bottom = 10
            };

            IntPtr ptrData = Marshal.AllocHGlobal(Marshal.SizeOf(sPUp));
            Marshal.StructureToPtr(sPUp, ptrData, false);
            IntPtr Result = HtmlHelp(ctrl.Handle, sHelpFileName + "::/" + sCSStreamName, HH_DISPLAY_TEXT_POPUP, ptrData);//(UInt32)
            Marshal.FreeHGlobal(ptrData);

        }
    }
}