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 aobject. 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:
Creating a Graphics object.
Using the Graphics object to draw lines and shapes, render text, or display and manipulate images.
Creating a Graphics Object
A graphics object can be created in a variety of ways.
To create a graphics object
Receive a reference to a graphics object as part of thein the 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.
Call themethod 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.
Create a Graphics object from any object that inherits from. This approach is useful when you want to alter an already existing image.
The following sections give details about each of these processes.
PaintEventArgs in the Paint Event Handler
When programming thefor controls, a graphics object is provided as one of the PaintEventArgs.
To obtain a reference to a Graphics object from the PaintEventArgs in the Paint event
Declare the Graphics object.
Assign the variable to refer to the Graphics object passed as part of the PaintEventArgs.
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:
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.
To create a Graphics object with the CreateGraphics method
Call the CreateGraphics method of the form or control upon which you want to render graphics.
Dim g as Graphics ' Sets g to a Graphics object representing the drawing surface of the ' control or form g is a member of. g = Me.CreateGraphics
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();
Create from an Image Object
Additionally, you can create a graphics object from any object that derives from the Image class.
To create a Graphics object from an Image
Call themethod, supplying the name of the Image variable from which you want to create a Graphics object.
The following example shows how to use aobject:
Bitmap myBitmap = new Bitmap(@"C:\Documents and Settings\Joe\Pics\myPic.bmp"); Graphics g = Graphics.FromImage(myBitmap);
You can only create Graphics objects from nonindexed .bmp files, such as 16-bit, 24-bit, and 32-bit .bmp files. Each pixel of nonindexed .bmp files holds a color, in contrast to pixels of indexed .bmp files, which hold an index to a color table.
Drawing and Manipulating Shapes and Images
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:
Theclass—Used for drawing lines, outlining shapes, or rendering other geometric representations.
Theclass—Used for filling areas of graphics, such as filled shapes, images, or text.
Theclass—Provides a description of what shapes to use when rendering text.
Thestructure—Represents the different colors to display.
To use the Graphics object you have created
Work with the appropriate object listed above to draw what you need.
For more information, see the following topics:
To render See