Introduction to GDI+ in .NET

Introduction

Microsoft .NET is Microsoft's recent released development framework. Microsoft .NET not only introduces powerful languages such as C# and VB.NET, it also brings relief to other programmers including graphics, multimedia, web development and speech.

In this article, we'll see basics of GDI+ and how GDI+ is much better interface than its predecessor GDI.

GDI - Graphic User Interface

GDI stands for Graphic Device Interface. In Microsoft Windows, GDI is a way to work with paining graphic objects such as painting on windows, forms or other media.

Why do you need GDI? To write GUI application, you need to write some kind of visual interface in the form of windows and controls. There is only one way to see the visual interface - through hardware, such as printer and monitor.

GDI is a set of C++ classes, which provides functionality to render data to a program to hardware devices with the help of device drivers. GDI sits between the program and the hardware and transfer data from one to other

Working with GDI objects in earlier versions of Microsoft products was a pain. I've been programming with Microsoft products (C++ and VB) for over 5 years in C++ and I know the pain of using GDI. If you've ever programmed in C++ or MFC, I bet you must be frustrated using GDI objects too. Have you ever try changing color or font of windows and controls in C++/MFC?

For example, if you want to change the font of a control in C++ (MFC), you need to create a font with its type and then call SetFont. See fig. 1.1.

CStatic *lpLabel=(CStatic *)GetDlgItem(IDC_STATIC1);
CFont LabelFont;
LabelFont.CreateFont(20,20,0,0,FW_BOLD,FALSE,FALSE,0,DEFAULT_CHARSET,             
   OUT_CHARACTER_PRECIS,CLIP_CHARACTER_PRECIS,DEFAULT_QUALITY, 
   DEFAULT_PITCH,NULL);
lpLabel->;SetFont(&LabelFont,TRUE);

Fig 1.1.

This is just a simple example. What if you want to change the background color of a toolbar? That's more pain. You need to override OnEraseBackground and get pDC object and so on.

GDI+: A Higher Level API

In Visual Studio .NET, Microsoft has taken care of most of the GDI problems and have made it easy to use. The GDI version of .NET is called GDI+.

GDI+ is next evolution of GDI. It's much better improved and easy to use version of GDI. The best thing about GDI is you don't need to know any details of drivers to render data on printers and monitors. GDI+ takes care of it for you. In other words, GDI was a low-middle level of programming API, where you need to know about devices too, while GDI+ is a higher level of programming model, which provides functions to do work for you.

For example, if you want to set background or foreground color of a control, just set ForeGroundColor property of the control. We'll see this all in more depth later in this tutorial.

What's new in GDI+?

Beside the fact that GDI+ API is easier and flexible than GDI, there are many more new features added to the API. Some of the new features GDI+ offers are -

• Improved Colors. Now GDI+ comes with more colors and these are compatible with other colors such as Windows etc.  
•    Antialiasing support  
•    Gradient brushes  
•    Splines  
•    Transformation and Matrices  
•    Scalable reasons  
•    Alpha Blending

It's hard to cover every thing in this article, but may be in next article of this series, I would cover some of these details.

What this article covers?

In this article, first we'll talk about GDI+ classes (also called types in .NET) and interfaces followed by GDI+ objects and then we'll see some sample examples.

GDI+ Class and Interfaces in .NET

In Microsoft .NET library, all classes (types) are grouped in namespaces. A namespace is nothing but a category of similar kind of classes. For example, Forms related classes are stored in Windows.Forms namespace, database related classed are grouped in Data and its sub namespaces such as System.Data.SqlClient, System.Data.OleDb, and System.Data.Common. Similarly, GDI+ classes are grouped under six namespaces, which reside in System.Drawing.dll assembly.

GDI+ Namespaces

GDI+ is defined in the Drawing namespace and its five sub namespaces. All drawing code resides in System.Drawing.DLL assembly. These namespaces System.Drawing, System.Drawing.Design, System.Drawing.Printing,  System.Drawing.Imaging, System.Drawing.Drawing2D and System.Drawing.Text namespaces. 

Now let's take a quick overview of these namespaces.

System.Drawing Namespace

The System.Drawing namespace provides basic GDI+ functionality. If contains the definition of basic classes such as Brush, Pen, Graphics, Bitmap, Font etc.  The Graphics class plays a major role in GDI+ and contains methods for drawing to the display device. The following table contains some of the System.Drawing namespace classes, structures and their definition.

Classes

Classes	Description
Bitmap, Image	Bitmap and image classes.
Brush, Brushes	Brush classes used define objects to fill GDI objects such as rectangles, ellipses, pies, polygons, and paths.
Font, FontFamily	Defines a particular format for text, including font face, size, and style attributes. Not inheritable.
Graphics	Encapsulates a GDI+ drawing surface. Not inheritable.
Pen	Defines an object used to draw lines and curves. Not inheritable.
SolidBrush, TextureBrush,	Defines a brush of a single color. Brushes are used to fill graphics shapes, such as rectangles, ellipses, pies, polygons, and paths. Not inheritable.

Structures

Structure	Description
Color	Represents an ARGB color.
Point, PointF	Represents a 2D x- and y-coordinates. Point takes x, y values as a number. You can use PointF if you want to use floating number values.
Rectangle, RectangleF	Represents a rectangle with integer values. A rectangle represents two point pair - top, left and bottom, right. You can use floating values in RectangleF.
Size	Size of a rectangular region with an ordered pair of width and height. Size takes an integer as width and height while SizeF takes floating numbers to represent width and height.

System.Drawing.Design Namespace

The System.Drawing.Design namespace is somewhat smaller in compare to the System.Drawing. It xtends design-time user interface (UI) logic and drawing functionality and provides classes for customizing toolbox and editor classes. For beginners there is nothing in this namespace. At present (.NET Beta 2) it has two types of classes -

Editor Classes

BitmapEditor, FontEditor, and ImageEditor are the editor classes. You can use these classes to extend the functionality and provide an option in properties window to edit images and fonts.

ToolBox Classes

ToolBoxItem, ToolBoxItemCollection are two major toolbox classes. By using these classes you can extend the functionality of toolbox and provide the implementation of toolbox items.

System.Drawing.Drawing2D Namespace

This namespace consists classes and enumerations for advanced 2-dimmensional and vector graphics functionality. It contains classes for gradient brushes, matrix and transformation and graphics path. Some of the common classes and enumerations are defined in the following tables -

Classes

Class	Description
Blend and ColorBlend	These classes define the blend for gradient brushes. The ColorBlend defines array of colors and position for multi-color gradient.
GraphicsPath	This class represents a set of connected lines and curves.
HatchBrush	A brush with hatch style, a foreground color, and a background color.
LinearGradientBrush	Provides a brush functionality with linear gradient.
Matrix	3x3 matrix represents geometric transformation.

Enumerations

Enumeration	Description
CombineMode	Different clipping types
CompositingQuality	The quality of compositing
DashStyle	The style of dashed lines drawn with a Pen.
HatchStyle	Represents different patterns available for HatchBrush
QualityMode	Specifies the quality of GDI+ objects.
SmoothingMode	Specifies the quality of GDI+ objects.

System.Drawing.Imaging Namespace

This namespace provides advanced GDI+ imaging functionality. It defines classes for metafile images. Other classes are encoder and decoder, which let you use any image format. It also defines a class PropertyItem, which let you store and retrieve information about the image files.  

System.Drawing.Printing Namespace

The System.Drawing.Printing namespace defines classes for printing functionality in your applications. Some of its major classes are defines in the following table -

Classes

Class	Description
PageSettings	Page settings
PaperSize	Size of a paper.
PreviewPageInfo	Print preview information for a single page.
PrintController	Controls document printing
PrintDocument	Sends output to a printer.
PrinterResolution	Sets resolution of a printer.
PrinterSettings	Printer settings

System.Drawing.Text Namespace

Even though most of the font's functionality is defined in System.Drawing namespace, this provides advanced typography functionality such as creating collection of fonts. Right now, this class has only three classes - FontCollection, InstalledFontCollection, and PrivateFontCollection. As you can see all of these classes are self-explanatory  

The Graphics Class

The Graphics class is center of all GDI+ classes. After discussing graphics class, I'll discuss some common GDI+ objects and their representation and then we'll see some sample applications to apply this theory in our applications and how it works.

The Graphics class plays a vital role in GDI+. No matter where you go, you go through this class ;). The Graphics class encapsulates GDI+ drawing surfaces. Before drawing any object (for example circle, or rectangle ) we have to create a surface using Graphics class.

There're different of ways to get a graphics object in your application. You can either get a graphics object on your form's paint event or by overriding OnPaint() method of a form. These both have one argument of type System.Windows.Forms.PaintEventArgs. You call its Graphics member to get the graphics object in your application. For example:

protected overrides sub OnPaint(ByVal e As 
                          System.Windows.Forms.PaintEventArgs)
      Dim g As Graphics = e.Graphics
End Sub 

Now you've the Graphics object. Now you can do any thing you want. The Graphics class has tons of methods to drawing graphics objects such as fonts, pens, lines, path and polygons, images and ellipse and so on. Some of the graphics class members are described in the following table -

DrawArc	This method draws an arc.
DrawBezier, DrawBeziers, DrawCurve	These methods draw a simple and bazier curves. These curvers can be closed, cubic and so on.
DrawEllipse	Draws an ellipse or circle.
DrawImage	Draws an image.
DrawLine	Draws a line.
DrawPath	Draws the path (lines with GraphicsPath )
DrawPie	Draws the outline of a pie section.
DrawPolygon	Draws the outline of a polygon.
DrawRectangle	Draws the outline of a rectangle.
DrawString	Draws a string.
FillEllipse	Fills the interior of an ellipse defined by a bounding rectangle.
FillPath	Fills the interior of a path.
FillPie	Fills the interior of a pie section.
FillPolygon	Fills the interior of a polygon defined by an array of points.
FillRectangle	Fills the interior of a rectangle with a Brush
FillRectangles	Fills the interiors of a series of rectangles with a Brush
FillRegion	Fills the interior of a Region.

Now say, if you want to draw an ellipse using the same method we've described above, you override OnPaint method and write the following code -

protected overrides sub OnPaint(ByVal e As 
                              System.Windows.Forms.PaintEventArgs)

Dim g As Graphics = e.Graphics
  Dim pn As Pen = New Pen(Color.Green, 10)
  g.DrawLine(pn, 100, 10, 30, 10)
  g.DrawEllipse(New Pen(Color.Red, 20), 20, 40, 20, 20)
  End Sub

That will draw a ellipse. Before we see more samples, let's discuss some GDI+ objects.

Common Graphics Objects

The graphics objects are the objects, which you use to draw your GDI+ items such as images, lines, rectangles, and path. For example, to fill a rectangle with a color, you need a color object and type of style you want to fill such as solid, texture and so on.

There are four common GDI+ objects, which you'll be using throughout your GDI+ life to fill GDI+ items. The major objects are:

Brush	Used to fill enclosed surfaces with patterns, colors, or bitmaps.
Pen	Used to draw lines and polygons, including rectangles, arcs, and pies
Font	Used to describe the font to be used to render text
Color	Used to describe the color used to render a particular object. In GDI+ color can be alpha blended

In GDI+, each of these object is represented by a class (also called type).

The Pen Class

A pen draws a line of specified width and style. You always use Pen constructor to create a pen. The constructor initializes a new instance of the Pen class. You can initialize it with a color or brush.

Initializes a new instance of the Pen class with the specified color.

Public Sub New(Color)

Initializes a new instance of the Pen class with the specified Brush.

Public Sub New(Brush)

Initializes a new instance of the Pen class with the specified Brush and width.

Public Sub New(Brush, Single)

Initializes a new instance of the Pen class with the

Dim pn as Pen = new Pen( Color.Blue )
 or
Dim pn as Pen = new Pen( Color.Blue, 100 )

specified Color and Width.

Public Sub New(Color, Single)

Here is one example:

Some of its most commonly used properties are:

Alignment	Gets or sets the alignment for objects drawn with this Pen.
Brush	Gets or sets the Brush that determines attributes of this Pen.
Color	Gets or sets the color of this Pen.
Width	Gets or sets the width of this Pen.

The Color Structure

A Color structure represents an ARGB color. Here are ARGB properties of it:

A	Gets the alpha component value for this Color.
B	Gets the blue component value for this Color.
G