Drawing a consecutive line on a form like MS paint on Winforms C#

c#, graphics, lines, winforms

Solution

I just implemented simple paint for you. Just create a new project and copy this code below to Form1.cs file. Comments in code should explain how it works.

public partial class Form1 : Form
{
    private Bitmap bmp; // Place to store our drawings
    private List<Point> points; // Points of currently drawing line
    private Pen pen; // Pen we will use to draw

    public Form1()
    {
        InitializeComponent();
        DoubleBuffered = true; // To avoid flickering effect

        bmp = new Bitmap(640, 480); // This is our canvas that will store drawn lines
        using (Graphics g = Graphics.FromImage(bmp))
            g.Clear(Color.White); // Let's make it white, like paper

        points = new List<Point>(); // Here we will remember the whole path
        pen = new Pen(Color.Black);

        MouseDown += OnMouseDown; // Start drawing
        MouseMove += OnMouseMove; // Drawing...
        MouseUp += OnMouseUp; // Stop drawing
        Paint += OnPaint; // Show the drawing
    }

    void OnPaint(object sender, PaintEventArgs e)
    {
        e.Graphics.DrawImage(bmp, 0, 0); // Show what is drawn
        if (points.Count > 0)
            e.Graphics.DrawLines(pen, points.ToArray()); // Show what is currently being drawn
    }

    void OnMouseDown(object sender, MouseEventArgs e)
    {
        if (e.Button != MouseButtons.Left)
            return;

        points.Clear();
        points.Add(e.Location); // Remember the first point
    }

    void OnMouseMove(object sender, MouseEventArgs e)
    {
        if (e.Button != MouseButtons.Left)
            return;

        points.Add(e.Location); // Add points to path
        Invalidate(); // Force to repaint
    }

    void OnMouseUp(object sender, MouseEventArgs e)
    {
        if (e.Button != MouseButtons.Left)
            return;

        SaveToBitmap(); // Save the drawn line to bitmap
        points.Clear(); // Our drawing is saved, we can clear the list of points
    }

    private void SaveToBitmap()
    {
        if (points.Count == 0)
            return;

        using (Graphics g = Graphics.FromImage(bmp))
            g.DrawLines(pen, points.ToArray()); // Just draw current line on bitmap
    }
}

Result:

Problem

Original source