Save User Drawn Bitmap Graphics in c#

Question

I have made a program that allows users to draw lines onto a picturebox image but now need to save these lines to be opened at a later date. This is my current code for drawing the lines:

 public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            pictureBox1.Image = new Bitmap(pictureBox1.Width, pictureBox1.Height);
        }
        int Drawshape;




        private Point p1, p2;
        List<Point> p1List = new List<Point>();
        List<Point> p2List = new List<Point>();

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {


        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            Drawshape = 5;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            Drawshape = 2;
        }

        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            if (Drawshape == 5)
            {
                if (p1.X == 0)
                {
                    p1.X = e.X;
                    p1.Y = e.Y;
                }
                else
                {
                    p2.X = e.X;
                    p2.Y = e.Y;

                    p1List.Add(p1);
                    p2List.Add(p2);

                    pictureBox1.Invalidate();
                    p1.X = 0;
                }
            }
        }

        private void pictureBox1_ParentChanged(object sender, EventArgs e)
        {

        }

        private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            Graphics G = Graphics.FromImage(pictureBox1.Image);
            if (Drawshape == 5)
            {
                using (var p = new Pen(Color.Blue, 4))
                {
                    for (int x = 0; x < p1List.Count; x++)
                    {
                        G.DrawLine(p, p1List[x], p2List[x]);
                    }
                }
            }

        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            pictureBox1.Invalidate();
        }

        private void Save_Click(object sender, EventArgs e)
        {



        } 
    }
}

I don't know how to save these lines and also open them again at a later time when the user wants to. I have put in open and save filedialogs but not sure how to make them do the job i want them to do. Please Help.

Thanks

Answer 1

If you want to save the image that is displayed in the picture box, complete with any lines that may have been drawn on top of it during run-time, you can use the Control.DrawToBitmap method.

I can't tell for sure if you're also asking how to use a SaveFileDialog to determine where the user wants to save the file or if you've already got that part figured out, but it's very simple.

Here's an example of a complete solution. First, the user is prompted by a save dialog (entitled "Save Image" and filtering to bitmap images (*.bmp) by default). If they click OK, the image displayed in the picture box is drawn to a temporary bitmap, and that temporary bitmap is saved to the location they specified. If they click Cancel, the file is not saved and the method simply exits.

private void Save_Click(object sender, EventArgs e)
{
    //Show a save dialog to allow the user to specify where to save the image file
    using (SaveFileDialog dlgSave = new SaveFileDialog())
    {
        dlgSave.Title = "Save Image";
        dlgSave.Filter = "Bitmap Images (*.bmp)|*.bmp|All Files (*.*)|*.*";
        if (dlgSave.ShowDialog(this) == DialogResult.OK)
        {
            //If user clicked OK, then save the image into the specified file
            using (Bitmap bmp = new Bitmap(pictureBox1.Width, pictureBox1.Height))
            {
                picturebox1.DrawToBitmap(bmp, new Rectangle(0, 0, bmp.Width, bmp.Height));
                bmp.Save(dlgSave.FileName);
            }
        }
    }
}