private void PictureBox1_MouseWheel(object sender, MouseEventArgs e)
    {
        if (e.Delta != 0)
        {
            if (e.Delta <= 0)
            {
                //set minimum size to zoom
                if (pictureBox1.Width < 350)
                    return;
            }
            else
            {
                //set maximum size to zoom
                if (pictureBox1.Width > 10000)
                    return;
            }

            int[] oldRectX = new int[rectList.Count];
            int[] oldRectY = new int[rectList.Count];
            int oldPictureBoxWidth = pictureBox1.Width;
            int oldPictureBoxHeight = pictureBox1.Height;

            for (int i = 0; i < rectList.Count; i++)
            {
                oldRectX[i] = rectList[i].rectangle.X;
                oldRectY[i] = rectList[i].rectangle.Y;
            }

            pictureBox1.Width += Convert.ToInt32(pictureBox1.Width * e.Delta / 1000);
            pictureBox1.Height += Convert.ToInt32(pictureBox1.Height * e.Delta / 1000);

            for (int i = 0; i < rectList.Count; i++)
            {
                rectList[i].rectangle.Width += Convert.ToInt32(rectList[i].rectangle.Width * e.Delta / 1000);
                rectList[i].rectangle.Height += Convert.ToInt32(rectList[i].rectangle.Height * e.Delta / 1000);

                rectList[i].rectangle.X = Convert.ToInt32(oldRectX[i] * (pictureBox1.Width / oldPictureBoxWidth));
                rectList[i].rectangle.Y = Convert.ToInt32(oldRectY[i] * (pictureBox1.Height / oldPictureBoxHeight));
                rectList[i].SetNewLocationOfSubRectList();
            }
            pictureBox1.Location = new Point((pictureBox1.Parent.ClientSize.Width / 2) - (pictureBox1.Width / 2), (pictureBox1.Parent.ClientSize.Height / 2) - (pictureBox1.Height / 2)); // Set the pictureBox1 to Center
            if (pictureBox1.Width > panel1.Width || pictureBox1.Height > panel1.Height)
            {
                Cursor = Cursors.Hand;
                mouseModeEnum = MouseMode.PANNING;
            }
            else
            {
                mouseModeEnum = MouseMode.NONE;
                Cursor = Cursors.Default;
            }
            pictureBox1.Invalidate();
        }
    }