How to: Create Graphics Objects for Drawing

Before you can draw lines and shapes, render text, or display and manipulate images with GDI+, you need to create a Graphics object. The Graphics object represents a GDI+ drawing surface, and is the object that is used to create graphical images.

There are two steps in working with graphics:

1. Creating a Graphics object.

2. Using the Graphics object to draw lines and shapes, render text, or display and manipulate images.

A graphics object can be created in a variety of ways.

• Receive a reference to a graphics object as part of the PaintEventArgs in the Paint event of a form or control. This is usually how you obtain a reference to a graphics object when creating painting code for a control. Similarly, you can also obtain a graphics object as a property of the PrintPageEventArgs when handling the PrintPage event for a PrintDocument.

  -or-

• Call the CreateGraphics method of a control or form to obtain a reference to a Graphics object that represents the drawing surface of that control or form. Use this method if you want to draw on a form or control that already exists.

  -or-

• Create a Graphics object from any object that inherits from Image. This approach is useful when you want to alter an already existing image.

  The following sections give details about each of these processes.

When programming the PaintEventHandler for controls or the PrintPage for a PrintDocument, a graphics object is provided as one of the properties of PaintEventArgs or PrintPageEventArgs.

1. Declare the Graphics object.

2. Assign the variable to refer to the Graphics object passed as part of the PaintEventArgs.

3. Insert code to paint the form or control.

   The following example shows how to reference a Graphics object from the PaintEventArgs in the Paint event:

   private void Form1_Paint(object sender,
      System.Windows.Forms.PaintEventArgs pe)
   {
      // Declares the Graphics object and sets it to the Graphics object
      // supplied in the PaintEventArgs.
      Graphics g = pe.Graphics;
      // Insert code to paint the form here.
   }
   

You can also use the CreateGraphics method of a control or form to obtain a reference to a Graphics object that represents the drawing surface of that control or form.

• Call the CreateGraphics method of the form or control upon which you want to render graphics.

  Graphics g;
  // Sets g to a graphics object representing the drawing surface of the
  // control or form g is a member of.
  g = this.CreateGraphics();
  

Additionally, you can create a graphics object from any object that derives from the Image class.

• Call the Graphics.FromImage method, supplying the name of the Image variable from which you want to create a Graphics object.

  The following example shows how to use a Bitmap object:

  Bitmap myBitmap = new Bitmap(@"C:\Documents and
     Settings\Joe\Pics\myPic.bmp");
  Graphics g = Graphics.FromImage(myBitmap);
  

After it is created, a Graphics object may be used to draw lines and shapes, render text, or display and manipulate images. The principal objects that are used with the Graphics object are:

• The Pen class—Used for drawing lines, outlining shapes, or rendering other geometric representations.

• The Brush class—Used for filling areas of graphics, such as filled shapes, images, or text.

• The Font class—Provides a description of what shapes to use when rendering text.

• The Color structure—Represents the different colors to display.

• Work with the appropriate object listed above to draw what you need.

  For more information, see the following topics:

  Expand table

  To render	See
  Lines	How to: Draw a Line on a Windows Form
  Shapes	How to: Draw an Outlined Shape
  Text	How to: Draw Text on a Windows Form
  Images	How to: Render Images with GDI+

• Getting Started with Graphics Programming
• Graphics and Drawing in Windows Forms
• Lines, Curves, and Shapes
• How to: Render Images with GDI+