CFbsRasterizer represents the system's rasterizer that has the ability to generate standard pixel data from data stored in proprietary formats.

Multiple formats of proprietary data may be supported by the rasterizer. Formats are identified by UID. Support for formats is platform-specific and controlled by the platform vendor. The OS does not mandate that the system's rasterizer must support any specific data formats.

CFbsRasterizer is used solely by the Font & Bitmap Server component to simulate pixel access to extended bitmaps, i.e. bitmaps created using CFbsBitmap::CreateExtendedBitmap(). CFbsRasterizer is not intended for use by applications.

CFbsRasterizer is intended to be implemented by licensees through derivation from the abstract base class. If a licensee wishes to provide a rasterizer implementation, they should create a rasterizer dll that is exported as "fbsrasterizer.dll" and include it in their ROM. Note that a stub rasterizer is exported to "fbsrasterizer.dll" and is loaded by the Font & Bitmap server by default to prevent a rogue dll being loaded in the rasterizer's place from the C:\ drive or removable media. Licensees can override this by using the following build option: -DFBSRASTERIZER_DLL <rasterizer_dll_name> where <rasterizer_dll_name> is the name of the licensee rasterizer dll.

CFbsRasterizer will be instantiated in client threads that use the Font & Bitmap Server, including the Window Server's main thread. Therefore the implementation of the rasterizer must be robust. Rasterizer functions should never lead to process termination, even when invalid proprietary data is passed in. Instances of CFbsRasterizer are not intended to be shared between threads.

The CFbsRasterizer interface has been designed to allow the implementation to optimise certain access patterns for performance. For example, the implementation might prepare for sequential access to a region by rasterizing the entire region inside a private scratch buffer. A further opportunity would be to take advantage of the immutability of extended bitmaps by maintaining rasterized scratch buffers for the most recently used bitmaps.