GDI: Basics

Simple GDI: Drawing a line on a form

by: juliet

This short and simple will teach you how to do simple graphics using GDI.NET

First you have have to build an empty windows form, if you don't know how to do this, please revise another tutorial: Hello World - Win Forms

After the form is build, you have to override the OnPaint event of the windows form by:

protected override void OnPaint(PaintEventArgs pe)  {

}

Then you will have to get a reference to the graphics object:

Graphics g = pe.Graphics;

Create an instance of the pen class using your favourite color:

Pen MyPen = new Pen(Color.Red);

Finally, create two points, and call the DrawLine() method of the graphics object, there you go !

Point a = new Point(50, 50);
Point b = new Point(250, 250);
g.DrawLine(MyPen, a, b);

Here is the complete code, remember to "using" System.Windows.Forms namespace and System.Drawing namespace:

using System;
using System.Windows.Forms;
using System.Drawing;


class myForm : Form {
    public myForm() {
        this.Text = "GDI Example";
    }
    
    protected override void OnPaint(PaintEventArgs pe) 
    { 
       Graphics g = pe.Graphics ; 
       
       Pen MyPen = new Pen(Color.Red);
       Point a = new Point(50, 50);
       Point b = new Point(250, 250);
       g.DrawLine(MyPen, a, b);
    } 
    
    public static void Main()
    {
        Application.Run(new myForm());
    }
}

You may compile this sample by:

csc /t:winexe /r:System.Windows.Forms.dll /r:System.Drawing.dll gdi.cs

(Type all things in one line, beware of line wrap)