Chapter 1

}
fontSpec));
The key function here is GetNearestFontInTwips(), a member function of
MGraphicsDeviceMap. You pass a TFontSpec to this function, and you get back a
pointer to a device-dependent font (a CFont*).
The mapping from TFontSpec to CFont* is ultimately handled by a graphics device
(though the font specification may be zoomed by a zoom factor). Once you have a CFont*,
you can only use it on the device that allocated it – more precisely, you can only use it for
drawing through a graphics context to the device that allocated it.
This function usually finds a match, but in the unlikely case that it doesn't, it returns an error
code. I propagate any error by calling User::LeaveIfError()
Notice the need to release the font after use; when you no longer need a CFont*, you must
ask the device to release it.
If you forget to release a font, the effect will be the same as a memory leak: your program
will get panicked on exit from emulator debug builds.
There is no error if ReleaseFont() is called when the font has not been allocated yet, the
function just returns. Therefore, it is safe to release the font at the start of the function. The
last font to be allocated before the application is closed is released in the hello control class
destructor.
The code iFont=NULL exists because of the possibility of the function leaving before the
font is reallocated. In this case, the destructor would attempt to release the font again if
iFont wasn't set to NULL, causing the application to crash.
The font specification uses the TFontSpec class, defined by the GDI, in gdi.h. Here's its
declaration:
class TFontSpec
{
public:
IMPORT_C TFontSpec();
IMPORT_C TFontSpec(const TDesC& aTypefaceName, TInt aHeight);
IMPORT_C TBool operator==(const TFontSpec& aFontSpec) const;
IMPORT_C void InternalizeL(RReadStream& aStream);
IMPORT_C void ExternalizeL(RWriteStream& aStream) const;
public:
TTypeface iTypeface;
TInt iHeight;
TFontStyle iFontStyle;
};
A font specification consists of a typeface, a height, and a font style. The TTypeface class
is also defined by the GDI. It has several attributes, of which the most important is the name.