A Professional HTML Renderer You Will Use

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.ComponentModel;

namespace System.Drawing.Html
{
    /// <summary>
    /// Provides HTML rendering on the tooltips
    /// </summary>
    public class HtmlToolTip
        : ToolTip
    {
        #region Fields

        private InitialContainer container;

        #endregion

        #region Ctor

        public HtmlToolTip()
        {

            OwnerDraw = true;

            Popup += new PopupEventHandler(HtmlToolTip_Popup);
            Draw += new DrawToolTipEventHandler(HtmlToolTip_Draw);

        }

        #endregion

        void HtmlToolTip_Popup(object sender, PopupEventArgs e)
        {
            string text = this.GetToolTip(e.AssociatedControl);
            string font = string.Format("font: {0}pt {1}", e.AssociatedControl.Font.Size, e.AssociatedControl.Font.FontFamily.Name);
            
            //Create fragment container
            container = new InitialContainer("<table class=htmltooltipbackground cellspacing=5 cellpadding=0 style=\"" + font + "\"><tr><td style=border:0px>" + text + "</td></tr></table>");
            container.SetBounds(new Rectangle(0, 0, 10, 10));
            container.AvoidGeometryAntialias = true;
            
            //Measure bounds of the container
            using (Graphics g = e.AssociatedControl.CreateGraphics())
            {
                container.MeasureBounds(g);
            }

            //Set the size of the tooltip
            e.ToolTipSize = Size.Round(container.MaximumSize);
            Console.WriteLine("Ttip: " + container.MaximumSize.ToString());

        }

        void HtmlToolTip_Draw(object sender, DrawToolTipEventArgs e)
        {
            e.Graphics.Clear(Color.White);

            if (container != null)
            {
                //Draw HTML!
                container.Paint(e.Graphics);
            }

        }
    }
}