Chapter 1

So far, we have suggested that you only need Draw() to do all your application's drawing.
Draw() gets called when necessary for system- initiated redraws, and you can use
DrawNow() to call Draw() for application-initiated redraws. However, there's a big problem
with this simplistic approach: it makes applications impossible to use.
Firstly, it makes them slow, because you do too much redrawing in response to the most
trivial updates. Secondly, it makes them ugly, because the draw-everything approach usually
causes unacceptable flicker while the display is drawn and redrawn.
Important
The art of graphics, in general, is making it look pretty. The art of onscreen
graphics is redrawing quickly and without flicker – and knowing
when to stop optimizing.
We'll use the Battleships views to show the most important considerations involved here.
Many Symbian OS applications are more complicated than Battleships and take these
considerations much further than I have done. In some cases, such as layout and updating
rich text, the logic is hideously complicated. Symbian OS provides a single, reusable
component for this purpose – FORM – so that application authors don't have to invent their
own.
The most important cases for updating the views are as follows:
� When we start the game, bring the game to the foreground, or reload a game, we have
to draw everything.
� When most events take place in the game, we have to redraw the status view.
� When something is hit, we have to reflect it in a fleet view – either my fleet or the
opponent's fleet.
� When the cursor is moved (on the opponent's fleet view), we have to move the
highlight quickly from the old cursor location to the new one.
Let's examine each of these in turn.
11.4.1 Drawing Everything
The draw-everything situations are fairly easy. The status view is very quick to draw and I
don't need to do anything special. I had more trouble with the fleet view, pictured in Figure
11.7: