Problem Zooming Image in PictureBox

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C#

picturebox

The image on picturebox go back to the original size and buffer gone broken infront
of the picturebox....
help me please...
this is the code...

public partial class ImageDetail : UserControl
    {
        public delegate void onClose();
        public event onClose close;
        Image pbImage;
        public ImageDetail(Image img)
        {            
            InitializeComponent();
            pictureBox.Image = img;
            pbImage = img;
            pictureBox.Width = this.pbImage.Width;
            pictureBox.Height = this.pbImage.Height;
            panel2.AutoScroll = true;
            panel2.HorizontalScroll.Maximum = img.Width;
            panel2.VerticalScroll.Maximum   = img.Height;
            panel2.HorizontalScroll.Minimum = 0;
            panel2.VerticalScroll.Minimum   = 0;
            panel2.SetAutoScrollMargin(10, 10);            
        }
        
        private void label2_Click(object sender, EventArgs e)
        {
            if (close != null)
                close(); 
        }        
        
        private void DrawImage(int startX, int startY)
        {            
            if (this.pbImage == null) { return; }
            
            Graphics pbGraphics = this.pictureBox.CreateGraphics();
            BufferedGraphicsContext currentGraphicsContext = BufferedGraphicsManager.Current;
            Rectangle targetRect = new Rectangle(startX, startY, (this.pbImage.Width + tmpWidth), (this.pbImage.Height + tmpHeight));
            using (BufferedGraphics pbGDIBuffer = currentGraphicsContext.Allocate(pbGraphics, targetRect))
            {
                Rectangle drawRect = new Rectangle(startX, startY, (this.pbImage.Width + tmpWidth), (this.pbImage.Height + tmpHeight));
                
                pbGDIBuffer.Graphics.DrawImageUnscaledAndClipped(this.pbImage, drawRect);
                pbGDIBuffer.Render();                
            }
            pictureBox.Width = this.pbImage.Width + tmpWidth;
            pictureBox.Height = this.pbImage.Height + tmpHeight;
        }             

        int tmpWidth = 0, tmpHeight = 0;
        private void toolStripSplitButton1_ButtonClick(object sender, EventArgs e)
        {
            tmpWidth = tmpWidth + ((this.pbImage.Width * 20) / 100);
            tmpHeight = tmpHeight + ((this.pbImage.Height * 20) / 100);
            
           pictureBox.Width = this.pbImage.Width + tmpWidth;
            pictureBox.Height = this.pbImage.Height + tmpHeight;
            pictureBox.Refresh();
            DrawImage(0, 0);
        }

        private void toolStripSplitButton2_ButtonClick(object sender, EventArgs e)
        {
            if(tmpWidth > 0)
                tmpWidth = tmpWidth - ((this.pbImage.Width * 20) / 100);
            if(tmpHeight > 0)
                tmpHeight = tmpHeight - ((this.pbImage.Height * 20) / 100);
            if (tmpHeight < 0)
                tmpHeight = 0;
            if (tmpWidth < 0)
                tmpWidth = 0;
            pictureBox.Refresh();
            DrawImage(0, 0);                      
        }

        private void panel2_MouseDown(object sender, MouseEventArgs e)
        {
            pictureBox.Width = this.pbImage.Width + tmpWidth;
            pictureBox.Height = this.pbImage.Height + tmpHeight;
        }

        private void panel2_MouseUp(object sender, MouseEventArgs e)
        {
            pictureBox.Width = this.pbImage.Width + tmpWidth;
            pictureBox.Height = this.pbImage.Height + tmpHeight;
        }
        
    }