Class COpenFontRasterizer

COpenFontRasterizer

Support

Supported from 5.0

Description

Font rasterizer abstract base class.

An Open Font System rasterizer is a polymorphic DLL. It contains a single exported factory function which creates rasterizer objects for a specific font type — these objects are derived from COpenFontRasterizer. This function is called just once, when the Font and Bitmap Server loads the DLL.

The rasterizer also implements, but does not export, the single pure virtual function declared in this class. The function reads font files, and creates a COpenFontFile object if the font file is of the right type.

Writing derived classes:

Open font rasterizers should derive from this class and implement the NewFontFileL() function.

Derived classes should also define the factory function. It is a static function which takes no arguments, and it is the only function exported from the class. It creates a COpenFontRasterizer derived object on the heap, and returns it to the caller — the caller is responsible for deleting the object. The name of the function does not matter because it is loaded by ordinal, however it is good practice to name it NewL(). As the name of the example function suggests, it is allowed to leave.

The rasterizer class may also need to store an 'engine context'. This is an object derived from COpenFontRasterizerContext, which provides functions that make it easier to write the glyph bitmap during rasterization.

More information on deriving from this class is provided in the API guide.

Derivation

CBase Base class for all classes to be instantiated on the heap COpenFontRasterizer Font rasterizer abstract base class

Defined in COpenFontRasterizer:
NewFontFileL()

Inherited from CBase:
operator new()

virtual COpenFontFile* NewFontFileL(TInt aUid,const TDesC& aFileName,RFs& aFileSession)=0;

Description

Creates a COpenFontFile derived object for loading font files in the new format.

This function is called by the framework during font and bitmap server startup. It creates a font file object for font files in the \system\fonts directory on all drives, using the default search path. The first font of a given name overrides subsequent ones. The directory search path is soft to hard: Y:, X:, W:, ..., C:, B:, A:, Z:. Files may also be added dynamically after startup using CWsScreenDevice::AddFile(), which indirectly calls this function.

Implementations of this function should examine the file aFileName, and if it is of the correct type attempt to create a COpenFontFile derived object to load it. The caller is responsible for deleting the object. The function must return NULL if it cannot recognise the file, and it may also leave if there is an error.

Parameters

TInt aUid An ID to be used for the file. UIDs are required by the font framework, so the font store allocates them for non Symbian-platform-native font files. This ID persists until the font is unloaded, e.g. if the device is rebooted. const TDesC& aFileName The full path and filename of the file from which the COpenFontFile object is created, if the file is the correct type. RFs& aFileSession The file session owned by the Font and Bitmap server. This file session should be used for any file access. If COpenFontFile objects need to keep files open, aFileSession should be stored in a place that is accessible to them.

Return value

COpenFontFile* A pointer to a new COpenFontFile derived object, or NULL if the file type is not recognised.

Leave codes

The function can leave if there is an error.

See also:

• CWsScreenDevice::AddFile()