C#

for(int i = pt1.X; i <= 40; )
{
   ...
}

using System;
using System.ComponentModel;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Windows.Forms;
 
public class Levels : Control
{
  int mixerId = -1;
  IntPtr hmx;
 
  const int CALLBACK_WINDOW = 0x00010000;
  const int MIXER_OBJECTF_MIXER = 0x0;
  const int MM_MIXM_CONTROL_CHANGE = 0x03d1;
 
  [DllImport("winmm.dll")]
  [return: MarshalAs(UnmanagedType.U4)]
  static extern int mixerOpen(out IntPtr phmx,
    [MarshalAs(UnmanagedType.U4)] int uMxId,
    IntPtr dwCallback, IntPtr dwInstance,
    [MarshalAs(UnmanagedType.U4)] int fdwOpen);
 
  [DllImport("winmm.dll")]
  [return: MarshalAs(UnmanagedType.U4)]
  static extern int mixerClose(IntPtr hmx);
 
  public Levels()
  {
    SetStyle(ControlStyles.AllPaintingInWmPaint |
      ControlStyles.UserPaint | ControlStyles.ResizeRedraw, true);
    SetStyle(ControlStyles.Selectable, false);
  }
 
  protected override void OnHandleCreated(EventArgs e)
  {
    base.OnHandleCreated(e);
 
    if (hmx != IntPtr.Zero)
      mixerClose(hmx);
 
    if (mixerId >= 0)
    {
      int result = mixerOpen(out hmx, mixerId, Handle, IntPtr.Zero,
        CALLBACK_WINDOW | MIXER_OBJECTF_MIXER);
      if (result != 0) throw new Win32Exception(result);
    }
  }
 
  protected override void WndProc(ref Message m)
  {
    base.WndProc(ref m);
 
    if (m.Msg == MM_MIXM_CONTROL_CHANGE)
    {
      Console.WriteLine("{0}: Received a message.", DateTime.Now);
    }
  }
 
  public int MixerId
  {
    get { return mixerId; }
    set { mixerId = value; }
  }
}
 
class Test : Form
{
  static void Main()
  {
    Application.Run(new Test());
  }
 
  Test()
  {
    Levels c = new Levels();
    Controls.Add(c);
    c.Location = new Point(8, 8);
    c.MixerId = 0;
  }
}