Operation of the Font and Bitmap Server

The use and relationships of the Font and Bitmap Server is summarised in the following diagram:

The server performs two main functions, bitmap sharing and font sharing:

The diagram shows a bitmap in the shared heap:

• Only the server may allocate into the heap.

• The server maintains a usage count for each object in the heap, and destroys objects when their usage count reaches zero.

The client may use a bitmaps graphics context to draw the bitmap directly:

• A single handle is passed to the window server to reference a unique shared bitmap.

• The window server uses a bitmaps graphics context to blit to the screen.

• A callback is needed - when the client releases, the window server buffer may not be flushed yet.

The server may move objects on the heap to maintain heap compactness — therefore a locking API is needed (cf. Begin() and End() in TBitmapUtil). To minimize this, only large bitmaps need locking — they use another heap.

• The server has a fontstore (not shown in diagram)

• Handles loading from removable media

• Fonts are released when their usage count reaches zero.