how to develop a crop selection control like photoshop's in c# 4.0 in widows form application.

I have a windows form application in c# 4.0 that can crop images. At first you have to draw a rectangle using mouse to select the cropped region

private Point _pt;
  private Point _pt2;
   private void picBoxImageProcessing_MouseDown(object sender, MouseEventArgs e)
    {

   if (e.Button == MouseButtons.Left)
   {
       int ix = (int)(e.X / _zoom);
       int iy = (int)(e.Y / _zoom);

       //reset _pt2
       _pt2 = new Point(0, 0);
       _pt = new Point(ix, iy);

       // pictureBox1.Invalidate();
       picBoxImageProcessing.Invalidate();
   }
}

 private void picBoxImageProcessing_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left && _selecting)
    {
       _selecting = false;
    }
 }

  private void picBoxImageProcessing_Paint(object sender, PaintEventArgs e)
  {


     if (_selecting &&_pt.X >= 0 && _pt.Y >= 0 && _pt2.X >= 0 && _pt2.Y >= 0)
        {

            e.Graphics.DrawRectangle(pen, _pt.X * _zoom, _pt.Y * _zoom, 
                      (_pt2.X - _pt.X)          *         _zoom, (_pt2.Y - _pt.Y) * _zoom);
         }
   } 

       private void picBoxImageProcessing_MouseMove(object sender, MouseEventArgs e)
      {


       if (e.Button == MouseButtons.Left)
        {
         _selecting = true;
         int ix = (int)(e.X / _zoom);
         int iy = (int)(e.Y / _zoom);

         _pt2 = new Point(ix, iy);

         //  pictureBox1.Invalidate();
           picBoxImageProcessing.Invalidate();
         }
     }

there is no problem to draw the rectangle by mouse dragging. But if i want to change the height or width of the rectangle then I have to draw a new rectangle, that i don't want. I want to change the height and width of the rectangle by modifying the drawn rectangle instead of drawing a new rectangle.
I don’t want to know how to crop. I need to draw a resizable rectangle on the image as we can do in photoshop.

So I need a crop selection control like photoshop's crop control.

Perhaps this article can help you out.

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