Chapter 1

Figure 4.1
At the bottom is the GDI, which defines the drawing primitives and everything necessary to
achieve device-independent drawing. The GDI is an entirely abstract component that has to
be implemented in various contexts – for on-screen pixel graphics, for instance, or in a
printer driver. I'll be covering the main drawing functions defined by the GDI in Chapter 11,
and its support for device-independent drawing in Chapter 15.
The BITGDI handles optimized rasterizing and bit blitting for on- screen windows and offscreen
bitmaps. The font and bitmap server (FBS) manages fonts and bitmaps – potentially
large graphics entities – for optimal space efficiency.
Support for user interaction starts with the window server, which manages the screen,
pointer or other navigation device, and any keypad or keyboard on behalf of all GUI
programs within the system. It shares these devices according to windowing conventions
that are easily understood by the average end user. A standard window is represented in the
client application programming interface API by the RWindow class.
The window server is a single server process that provides a basic API for client applications
to use. CONE, the control environment, runs in each application process and works with the
window server's client-side API, to allow different parts of an application to share windows,
key and pointer events. A fundamental abstract class delivered by CONE is CCoeControl,a
control, which is a unit of user interaction that uses any combination of screen, keyboard,
and pointer. Many controls can share a single window. Concrete control types are derived
from CCoeControl.
CONE doesn't provide any concrete controls: that's the job of Uikon, the system GUI, and
any UI-specific layer, such as Qikon. Together, they specify a standard look-and-feel, and
provide reusable controls and other classes that implement that look-and-feel.
4.3 Application Structure
By studying the code and the execution of the GUI version of 'Hello world!', we'll begin to
understand how Symbian OS GUI applications fit together, using the frameworks provided
by Uikon and the application architecture (APPARC).