PanelHandle Control

    public class PanelHandle : Panel
    {
        public PanelHandle()
        {
            SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint | ControlStyles.ResizeRedraw | ControlStyles.OptimizedDoubleBuffer, true);
            this.BorderColor = Color.Black;
            this.Border = DefaultBorder;
        }

        public enum HitTest
        {
            Nowhere = 0,
            Client = 1,
            Caption = 2,
            Left = 10,
            Right = 11,
            Top = 12,
            TopLeft = 13,
            TopRight = 14,
            Bottom = 15,
            BottomLeft = 16,
            BottomRight = 17,
            Border = 18
        }

        #region Properties
        private static Padding DefaultBorder = new Padding(6);
        private Padding border;
        private Color bordercolor;

        [Description("Defines the resizing border to be drawn")]
        public Padding Border
        {
            get { return this.border; }
            set
            {
                this.border = value;
                InvalidateEx();
            }
        }

        [DefaultValue(typeof(Color), "Black"),
        Description("Set the color of the border")]
        public Color BorderColor
        {
            get { return bordercolor; }
            set
            {
                bordercolor = value;
                InvalidateEx();
            }
        }
        #endregion

        #region Methods
        private void InvalidateEx()
        {
            if (this.Parent == null)
                return;

            Parent.Invalidate(new Rectangle(this.Location, this.Size), true);
        }

        private IntPtr calcNCHitTest(Rectangle rec)
        {
            IntPtr ret = IntPtr.Zero;

            // Check if it's in the middle region (not touching any borders)
            if (rec.Location.Y > Border.Top &&
                rec.Location.Y < rec.Height - Border.Bottom &&
                rec.Location.X > Border.Left &&
                rec.Location.X < rec.Width - Border.Right)
                ret = (IntPtr)HitTest.Caption;

            // Left
            else if (rec.Location.Y >= Border.Top &&
                rec.Location.Y <= rec.Height - Border.Bottom &&
                rec.Location.X < Border.Left)
                ret = (IntPtr)HitTest.Left;


            // Top
            else if (rec.Location.Y < Border.Top &&
                rec.Location.X >= Border.Left &&
                rec.Location.X <= rec.Width - Border.Right)
                ret = (IntPtr)HitTest.Top;

            // Right
            else if (rec.Location.Y >= Border.Top &&
                rec.Location.Y <= rec.Height - Border.Bottom &&
                rec.Location.X > rec.Width - Border.Right)
                ret = (IntPtr)HitTest.Right;

            // Bottom
            else if (rec.Location.Y > rec.Height - Border.Bottom &&
                rec.Location.X >= Border.Left &&
                rec.Location.X <= rec.Width - Border.Right)
                ret = (IntPtr)HitTest.Bottom;

            // Top-left
            else if (rec.Location.Y < Border.Top &&
                rec.Location.X < Border.Left)
                ret = (IntPtr)HitTest.TopLeft;

            // Top-right
            else if (rec.Location.Y < Border.Top &&
                rec.Location.X > rec.Width - Border.Right)
                ret = (IntPtr)HitTest.TopRight;

            // Bottom-left
            else if (rec.Location.Y > rec.Height - Border.Bottom &&
                rec.Location.X < Border.Right)
                ret = (IntPtr)HitTest.BottomLeft;

            // Bottom-right
            else if (rec.Location.Y > rec.Height - Border.Bottom &&
                rec.Location.X > rec.Width - Border.Right)
                ret = (IntPtr)HitTest.BottomRight;

            return ret;
        }

        private Point calcHitPoint(IntPtr lParam)
        {
            int x = (lParam.ToInt32() << 16) >> 16;
            int y = lParam.ToInt32() >> 16;
            return PointToClient(new Point(x, y));
        }

        private void ChangeColor(int wParam)
        {
            using (ColorDialog cd = new ColorDialog())
            {
                cd.AnyColor = true;
                cd.FullOpen = true;
                switch (wParam)
                {
                    case 2:
                        cd.Color = this.BackColor;
                        if (cd.ShowDialog() == DialogResult.OK)
                            this.BackColor = cd.Color;
                        break;
                    default:
                        cd.Color = this.BorderColor;
                        if (cd.ShowDialog() == DialogResult.OK)
                            this.BorderColor = cd.Color;
                        break;
                }
            }
        }

        bool ShouldSerializeBorder()
        {
            return Border != DefaultBorder;
        }

        void ResetBorder()
        {
            this.Border = DefaultBorder;
        }
        #endregion

        #region Overrides
        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);
            switch (m.Msg)
            {
                case 0x84:
                    Rectangle rec = new Rectangle(calcHitPoint(m.LParam), ClientSize);
                    IntPtr res = calcNCHitTest(rec);

                    m.Result = res;
                    break;
                case 0x216:
                    this.BringToFront();
                    break;
                case 0x214:
                    this.BringToFront();
                    break;
                case 0xA5:
                    ChangeColor(m.WParam.ToInt32());
                    break;
            }
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            using (System.Drawing.Drawing2D.GraphicsPath gp = new System.Drawing.Drawing2D.GraphicsPath())
            {
                using (SolidBrush b = new SolidBrush(BorderColor))
                {
                    e.Graphics.FillRectangle(b, 0, 0, Border.Left, ClientSize.Height);                                  // Draw left border
                    e.Graphics.FillRectangle(b, 0, 0, ClientSize.Width, Border.Top);                                    // Draw top border
                    e.Graphics.FillRectangle(b, ClientSize.Width - border.Right, 0, Border.Right, ClientSize.Height);   // Draw right border
                    e.Graphics.FillRectangle(b, 0, ClientSize.Height - border.Bottom, ClientSize.Width, Border.Bottom); // Draw bottom border
                }
            }
            base.OnPaint(e);
        }
        #endregion
    }