Teach Yourself Borland C++ in 14 Days - portal

160 Day 5
Tucked into this group of classes is the TMediaPlayer class. This class allows you to play media
files like WAV audio, AVI video, and MIDI audio. The media can be played, stopped,
paused, or positioned at a particular point in the file, as well as many other operations. This
class has many properties and events that greatly simplify the complex world of the Windows
Media Control Interface (MCI).
The System group includes OLE and dynamic data exchange (DDE) classes as well.
GDI Classes
The GDI (graphics device interface) classes typically get a lot of work in Windows GUI
applications. These classes encapsulate the use of bitmaps, fonts, device contexts (DCs),
brushes, and pens. It is through these GDI objects that graphics and text are displayed on a
window. The GDI classes are not associated with a specific component, but many components
have instances of these classes as properties. For example, an edit control has a property
called Font that is an instance of the TFont class.
The term device context is well known by Windows programmers whether they program in
C or with one of the C++ frameworks. In VCL, though, the term is not widely used. This
is because VCL calls DCs canvases and encapsulates the complex world of DCs in the TCanvas
class. A canvas provides a surface that you can draw on using methods like MoveTo(),
LineTo(), and TextOut(). Bitmaps can be displayed on the canvas using the Draw() or
StretchDraw() methods. The concept of a canvas that you draw on makes more sense than
the archaic term device context, don’t you think?
The TCanvas class contains instances of the other GDI classes. For example, when you do a
MoveTo()/LineTo() sequence, a line is drawn with the current pen color. The Pen property is
used to determine the current pen color and is an instance of the TPen class. TPen has properties
that determine what type of line to draw: the line width, the line style (solid, dashed, dotted,
and so on), and the mode with which to draw the line.
The TBrush class represents a brush that is used as the fill pattern for canvas operations like
FillRect(), Polygon(), and Ellipse(). TBrush properties include Color, Style, and Bitmap.
The Style property allows you to set a hatch pattern for the brush. The Bitmap property allows
you to specify a bitmap that will be used for the fill pattern.
TBitmap encapsulates bitmap operations in VCL. Properties include Palette, Height, Width,
and TransparentColor. Methods include LoadFromFile(), LoadFromResourceID(), and
SaveToFile(). TBitmap is used by other component classes such as TImage, TBitBtn, and
TSpeedButton in addition to TCanvas.
The TFont class handles font operations. Properties include Color, Height, and Style (bold,
italic, normal, and so on). The TFont class is used by all component classes that display text.