Working with Graphics in .NET

It is found sometimes that the graphics form of data provides better mode of communication since it can enhance the user interface of the application by representing the data in clear, concise and lucid manner. Some of the tasks that use graphics are inserting graphical charts and reports in documents, creating new or editing existing images, drawing customized shapes, logos, etc. in the documents wherever it is necessary.

The .Net framework provides umpteen numbers of options to create and edit graphics through a variety of programming techniques. The Graphics feature in .Net has been mostly implemented in a set of managed classes in the namespaces, System.Drawing, System.Drawing.Drawing2D, System.Drawing.Imaging, System.Drawing.Printing and System.Drawing.Text. These classes that help in custom drawing on the screen forms the GDI+ (Graphics Device Interface) object model of .Net framework. These classes are very intuitive and easy to use. The services provided in this model can be categorized into the following sections:

• Drawing basic graphics like line, rectangle, etc.

• Creating and using images, bitmaps, icons, etc.

• Formatting the text content to different size and shapes

Principles of GDI+

The main aim of the GDI+ is to abstract the details of the device in which the output is displayed and hence enable developers to build device independent applications. GDI+ is basically derived from GDI that was included in earlier version of Windows. GDI+ involves the device context (DC) object which represents the device in which the output is displayed. This DC object stores information about a particular output device (printer, monitor, etc.) and takes care of translating the calls from the operating system to the device. The class, System.Drawing.Graphics class wraps this functionality of device context and is used for handling all the drawing operations.

Drawing graphics

Some of the classes that implement the logic for drawing two-dimensional graphics are Brush, Font, Icon, Image, Pen, etc. The names of the classes are self-explanatory to the service they provide. In addition to these classes, the Graphics class is used to draw to the display device. The Pen class is used to draw lines and curves while the classes derived from Brush are used to fill the interiors of the shapes.

There are also few structures like Point, Color, Rectangle and Size which are used to specify the details of an object which can be of more than one value. For example, by using a Point structure, the co-ordinates of a control (Button1) to be 10 pixels from the upper-left corner of the form in which it resides can be specified as below:

Button1.Location = new Point (10, 10);
Following can be the steps to draw a line or any two-dimensional figure in a Windows Form using .Net classes:

• Creating a Graphics object by means of calling the System.Windows.Forms.Control.CreateGraphics method.

• Creating the Pen object and to specify the color and width in pixels.

• Draw a line or any shape by calling the Graphics member methods and by using the Pen instance created. Some of the methods of Graphics class are DrawEllipse, DrawImage, DrawLine, DrawPie, DrawPolygon, etc. Each of these members is overloaded with different methods through which the figure can be drawn.
Following are the steps to draw solid shape filled with color:

• Create a Graphics object by calling the System.Windows.Forms.Control.CreateGraphics method.

• Create a Brush object and specify the filling pattern and color (by choosing the required derived class of Brush class).

• Call the required Fill method of Brush class and then the Draw method.

Working with Images

The framework provides classes, Image and Bitmap for working with a variety of image formats which need to be edited in applications. Image class helps to create, load, modify and save drawings, add copyright information to a picture and resize JPEG images to a lesser size for faster downloading. Bitmap is another useful class derived from Image and can be used for handling still images. The ability that Bitmap possess and Image class does not is that Bitmap is able to control the Color object pertaining to a pixel in an image to the required color.

Pictures can be displayed in a Windows form in two different ways. The first option is to call method, FromFile of Image object and set this as background image of a PictureBox control. The other option is to use Bitmap object loaded with the image and pass it as parameter to the method, DrawImage of the Graphics object.

Icons are transparent bitmaps of standard size, 40 by 40 pixels provided by the framework. For displaying icons, method, Graphics.DrawIcon or Graphics.DrawIconUnstretched is called.

Handling text

The framework has also provided classes for adding text to images in a variety of size, font and style for labeling and reporting purposes. The Graphics class is mainly used for this. To write text, call the Graphics.DrawString method by specifying the Font and Brush (Font object for specifying the shape of the characters of text) objects with the location to draw the text. The StringFormat class is used to specify alignment, text direction, LineLimit, etc. and is passed to the DrawString method to display the text in the required format.

Thus, the GDI+ model of the .Net framework facilitates as a powerful tool to display customized and complex figures to the specific output device through simple statements. However, it is important to understand the principles of GDI+ and the design of Windows architecture to use it efficiently and effectively.

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