The API for the presentation layer has been designed following the drivers metaphor used in operating systems to give a common interface to complex and versatile peripherals. L211 L212 L218 L217 calling one of the predefined set of functions available at the driver interface. Once a context has been set-up it can be reused for multiple requests on to the driver. Currently the API consists of two drivers, one for handling specific presentation control and one for the generic presentation control. FC T P presentdriver.h L398 .
All function are one of both types, depending wether they are used to set or retrieve information.
All value provided to the drivers should be typed, this is the role of the unit field. Used for example for defining font size relative to the font size of the englobing element. Some more unit will be added as the drivers and the rendering engine are extended to support more functionnalities. Depending on the driver, the two first arguments of a driver function will differs. L423 L422 L421 It contains a pointer to the SpecificDriver, the document identifier and the associated Structure Schema.