Chapter 1

virtual void DrawBitmap(const TRect& aDestRect,
const CFbsBitmap* aSource,
const TRect& aSourceRect) = 0;
Use the same-size variant for high-performance blitting of GUI icons and the stretch-blit
variants for device-independent view code supporting on-screen zooming or printing.
Note
See Chapter 15 for more on drawing bitmaps.
Text
You can draw text in the current font. Here are the functions for doing so:
virtual void DrawText(const TDesC& aString,
const TPoint& aPosition) = 0;
virtual void DrawText(const TDesC& aString,
const TRect& aBox,
TInt aBaselineOffset,
TTextAlign aHoriz = ELeft,
TInt aLeftMrg = 0) = 0;
The first (and apparently simpler) function uses the GC's justification settings, but you
shouldn't call it yourself. Instead, use FORM if you need to handle properly laid out text. For
general use, use the TRect variant that clips the text to the specified rectangle, and paints
the rectangle background with the current brush.
Important
A graphics context has no default font and if you call a text-drawing
function without a previous call to UseFont() in effect, you get a
panic.
The panic is particularly ugly when you're drawing to a CWindowGc because all windowdrawing
functions are batched together and sent to the window to be executed later. The
window server doesn't detect the absence of a UseFont() until the buffer is executed by
which time there is no context information about where the panic occurred. Always
remember to use DiscardFont() to discard the font after use and so avoid a memory
leak.
11.3 Drawing and Redrawing
In a GUI program, all drawing is done to controls, which form all or part of a screen window
as we saw with hellogui's CHelloGuiAppView::Draw():
� The derived control class's Draw() function is called when drawing is required.
� Draw() gets a graphics context using SystemGc().
� It draws into the area defined by its Rect() function.
But it's a bit more complicated than that. Your control must not only draw its content but
must also redraw it when it changes, or when the system requires a redraw.
System-initiated redraws occur when:
� the window is first constructed;
� the window, or part of it, is exposed after having been obscured by some other
application or a dialog box.