The Structure of the Class-Based Interface
The C++ interface to Windows GDI+ contains about 40 classes, 50 enumerations, and 6 structures. There are also a few functions that are not members of any class.
You must indicate that the namespace Gdiplus is being used before any GDI+ functions are called. The following statement indicates that the Gdiplus namespace is being used in the application.
using namespace Gdiplus;
The Graphics class is the core of the GDI+ interface; it is the class that actually draws lines, curves, figures, images, and text.
Many classes work together with the Graphics class. For example, the Graphics::DrawLine method receives a pointer to a Pen object, which holds attributes (color, width, dash style, and the like) of the line to be drawn. The Graphics::FillRectangle method can receive a pointer to a LinearGradientBrush object, which works with the Graphics object to fill a rectangle with a gradually changing color. Font and StringFormat objects influence the way a Graphics object draws text. A Matrix object stores and manipulates the world transformation of a Graphics object, which is used to rotate, scale, and flip images.
Certain classes serve primarily as structured data types. Some of those classes (for example, Rect, Point, and Size) are for general purposes. Others are for specialized purposes and are considered helper classes. For example, the BitmapData class is a helper for the Bitmap class, and the PathData class is a helper for the GraphicsPath class. GDI+ also defines a few structures that are used for organizing data. For example, the ColorMap structure holds a pair of Color objects that form one entry in a color conversion table.
GDI+ defines several enumerations, which are collections of related constants. For example, the LineJoin enumeration contains the elements LineJoinBevel, LineJoinMiter, and LineJoinRound, which specify styles that can be used to join two lines.
GDI+ provides a few functions that are not part of any class. Two of those functions are GdiplusStartup and GdiplusShutdown. You must call GdiplusStartup before you make any other GDI+ calls, and you must call GdiplusShutdown when you have finished using GDI+.