The example Draw smooth shapes in a form's Paint event handler in C# shows how to draw a picture in a form's Paint event handler. This is simple but the Paint event is raised every time the form grows larger or is covered and then exposed. If the drawing takes a long time, then the event handler can take a little while and the user may notice.

This example shows how to draw on a Bitmap once when the form loads. It sets a PictureBox control's Image property to the Bitmap and the PictureBox automatically redisplays it whenever necessary with no redrawing.

The following code shows how the example draws its picture.

// Make and display a Bitmap.
private void Form1_Load(object sender, EventArgs e)
{
    // Prepare the PictureBox.
    picDrawing.SizeMode = PictureBoxSizeMode.AutoSize;
    picDrawing.Location = new Point(0, 0);

    // Make the Bitmap.
    Bitmap bm = new Bitmap(280, 110);

    // Draw on it.
    using (Graphics gr = Graphics.FromImage(bm))
    {
        // Draw smoothly.
        gr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;

        // Make a Rectangle to define the ellipse.
        Rectangle rect = new Rectangle(10, 10, 260, 90);

        // Fill the ellipse.
        gr.FillEllipse(Brushes.LightGreen, rect);

        // Outline the ellipse.
        using (Pen thick_pen = new Pen(Color.Blue, 5))
        {
            gr.DrawEllipse(thick_pen, rect);
        }
    }

    // Display the Bitmap.
    picDrawing.Image = bm;
}

First the code prepares its PictureBox by setting SizeMode = AutoSize and moving the PictureBox into the form's upper left corner. (You could do this at design time but I wanted to the code emphasize the fact that SizeMode = AutoSize. That guarantees that the Bitmap is completely visible.)

Next the program makes a Bitmap and a Graphics object to draw on it.

The code sets the Graphics object's SmoothingMode property to get smooth drawing. It creates a Rectangle to define the ellipse, fills the ellipse, and then outlines it with a thick pen.

After all of the drawing, the code sets the PictureBox's Image property to the Bitmap.