C#

const int WM_MOVE = 0x0003;
 
protected override void WndProc(ref Message m) {
	if (!m.Msg==WM_MOVE) base.WndProc(ref m);
} 

private const int WM_MOVING = 0x0216;

[StructLayout(LayoutKind.Sequential)]
struct RectangleStructure
{
    public int Left;
    public int Top;
    public int Right;
    public int Bottom;
}

protected override void WndProc(ref Message m)
{
    if (m.Msg == WM_MOVING)
    {
        RectangleStructure rectangle =
            (RectangleStructure)Marshal.PtrToStructure(m.LParam, typeof(RectangleStructure));
        if (rectangle.Left < LeftLimit)
        {
            rectangle.Right = LeftLimit + Width;
            rectangle.Left = LeftLimit;
            Marshal.StructureToPtr(rectangle, m.LParam, true);
        }
        if (rectangle.Top < TopLimit)
        {
            rectangle.Bottom = TopLimit + Height;
            rectangle.Top = TopLimit;
            Marshal.StructureToPtr(rectangle, m.LParam, true);
        }
        if (rectangle.Right > RightLimit)
        {
            rectangle.Left = RightLimit - Width;
            rectangle.Right = RightLimit;
            Marshal.StructureToPtr(rectangle, m.LParam, true);
        }
        if (rectangle.Bottom > BottomLimit)
        {
            rectangle.Top = BottomLimit - Height;
            rectangle.Bottom = BottomLimit;
            Marshal.StructureToPtr(rectangle, m.LParam, true);
        }
    }
    base.WndProc(ref m);