Chapter 1

I'm careful to draw every pixel: I use DrawUtils::DrawBetween-Rects() to whiten the
region between the rectangle to be drawn and the outside of the control. I then use the pen
to draw a rectangle on the inside of the border. Then the rectangle is shrunk by a pixel and
passed to the hello view's draw function.
The fundamental point that this example does show is that you can implement drawing code
that's completely independent of a control and completely independent of the screen device.
15.1.3 Managing the Zoom Factor
We have already claimed that a device map ultimately uses a real device.
CExampleHelloControl shows how the zoom factor relates to the device. Here's the
declaration of TZoomFactor in gdi.h:
class TZoomFactor : public MGraphicsDeviceMap
{
public:
IMPORT_C TZoomFactor();
IMPORT_C ~TZoomFactor();
inline TZoomFactor(const MGraphicsDeviceMap* aDevice);
IMPORT_C TInt ZoomFactor() const;
IMPORT_C void SetZoomFactor(TInt aZoomFactor);
inline void SetGraphicsDeviceMap(const MGraphicsDeviceMap*
aDevice);
public:
inline const MGraphicsDeviceMap* GraphicsDeviceMap() const;
IMPORT_C void SetTwipToPixelMapping(const TSize& aSizeInPixels,
const TSize& aSizeInTwips);
IMPORT_C TInt HorizontalTwipsToPixels(TInt aTwipWidth) const;
IMPORT_C TInt VerticalTwipsToPixels(TInt aTwipHeight) const;
IMPORT_C TInt HorizontalPixelsToTwips(TInt aPixelWidth) const;
IMPORT_C TInt VerticalPixelsToTwips(TInt aPixelHeight) const;
IMPORT_C TInt GetNearestFontInTwips(CFont*& aFont,
IMPORT_C void ReleaseFont(CFont* aFont);
enum {EZoomOneToOne = 1000};
private:
TInt iZoomFactor;
const MGraphicsDeviceMap* iDevice;
};
const TFontSpec& aFontSpec);
TZoomFactor both implements MGraphicsDeviceMap's interface and uses a
MGraphicsDeviceMap. TZoomFactor contains an integer, iZoomFactor, which is set to
1000 to indicate a one-to-one zoom, and proportionately for any other zoom factor.