## Presentation Device Driver Reference for OS/2

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### Journal Functions (Hardcopy Drivers Only)

Journal functions allow presentation drivers to optimize the processing of data for raster devices such as dot-matrix or laser printers, which print bands of data. The size of a band is determined by the type of device and the amount of memory the driver can use to build its bit map. As an example , a color laser printer might need the full 24 bits per pel. In this case, several bands might be needed to make a page. A simple dot-matrix printer that uses one bit per pel could treat the whole page as a single band. Refer to Banding for a description of how a presentation driver would use journaling functions to perform the technique of banding.

The hardcopy driver creates a journal file when the DC is enabled and starts recording in response to GreEscape (DEVESC_STARTDOC). The graphics engine stores the Grexxx functions in the journal file as they are passed to the DC until told to stop recording by the hardcopy driver.

If the presentation driver passes the bit flag JNL_DRAW_OPTIMIZATION when it calls GreCreateJournalFile, the hardcopy driver processes the calls to produce the first band while the journal file is being accumulated. Otherwise, the COM_DRAW command bit flag is turned OFF and the hardcopy driver is, in effect, told not to draw while the journal file is being accumulated.

When the journal file is complete, if the JNL_DRAW_OPTIMIZATION bit flag was set ON when the function GreCreateJournalFile was called, the hardcopy driver passes the completed band to the spooler or hardcopy device. It then plays the journal file and reprocesses the calls to produce the next band. Otherwise, the hardcopy driver plays the journal file and reprocesses the calls to produce all bands, including the first.