Chapter 1

IMPORT_C virtual void Draw(const TRect& aRect) const;
...
};
Use the functions as follows:
� You have to activate a control using ActivateL() as the final part of its secondphase
construction. Assuming that by the time ActivateL() is called, the control's
extent is in place and its model is fully initialized makes the control ready for drawing.
You can use IsActivated() to test whether ActivateL() has been called.
� You can set a control to be visible or not – Draw() is not called for invisible controls.
� IsReadyToDraw() returns ETrue if the control is both activated and visible.
� SetBlank() is an obscure function that only affects controls that don't override
Draw(). If you don't SetBlank(), then CCoeControl::Draw() does nothing. If you
do SetBlank(), then CCoeControl::Draw() blanks the control.
� We have already seen that Draw() is the fundamental drawing function. DrawNow()
initiates the correct drawing sequence to draw a control and all its components.
� DrawDeferred() simply invalidates the control's extent so that the window server will
send a redraw message, causing a redraw later. This guarantees that a redraw will be
called on the control at the earliest available opportunity, rather than forcing it now.
� ActivateL(), MakeVisible(), and DrawNow() recurse as appropriate through
component controls.
� SystemGc() returns a windowed GC for drawing. ActivateGc(), ResetGc(), and
DeactivateGc() perform the GC preparation functions needed for redrawing.
Important Always use these functions, rather than directly calling
SystemGc.Activate(Window()). It's more convenient and it
allows control contexts to be supported properly.
11.7 Special Effects
The window server provides many useful special effects to application programs. These
include:
� Shadows
� Backed-up-behind Windows
� Animation
� Use of debug keys
� Using a control context
� Scrolling.
We'll examine each of these in turn.
Important
Note that the availability of these special effects depends on the
implementation that you are using. UIQ for example, does not use
shadows; instead it fades the background.
11.7.1 Shadows
Shadows can be used in many circumstances – behind dialogs, behind menus, behind
popup choice lists and so on. Not all Symbian OS implementations use shadows. UIQ, for
example, fades the background behind a window and so does not implement shadows.
You have to specify that you want a window to cast a shadow and say how 'high' the window
is. The shadow actually falls on the window(s) behind the one that you specify to cast
shadows. To implement a shadow when it is cast, the window server asks the BITGDI to dim