Driver Functions

A dispatch table is used to direct function calls to whatever driver is chosen at run-time. Below are listed the names of each entry in the PLDispatchTable dispatch table struct defined in plcore.h. The entries specific to each device (defined in drivers/*.c) are typically named similarly but with "pl_" replaced by a string specific for that device (the logical order must be preserved, however). The dispatch table entries are :

• pl_MenuStr: Pointer to string that is printed in device menu.

• pl_DevName: A short device "name" for device selection by name.

• pl_type: 0 for file-oriented device, 1 for interactive (the null driver uses -1 here).

• pl_init: Initialize device. This routine may also prompt the user for certain device parameters or open a graphics file (see Notes). Called only once to set things up. Certain options such as familying and resolution (dots/mm) should be set up before calling this routine (note: some drivers ignore these).

• pl_line: Draws a line between two points.

• pl_polyline: Draws a polyline (no broken segments).

• pl_eop: Finishes out current page (see Notes).

• pl_bop: Set up for plotting on a new page. May also open a new a new graphics file (see Notes).

• pl_tidy: Tidy up. May close graphics file (see Notes).

• pl_state: Handle change in PLStream state (color, pen width, fill attribute, etc).

• pl_esc: Escape function for driver-specific commands.

Notes: Most devices allow multi-page plots to be stored in a single graphics file, in which case the graphics file should be opened in the pl_init() routine, closed in pl_tidy(), and page advances done by calling pl_eop and pl_bop() in sequence. If multi-page plots need to be stored in different files then pl_bop() should open the file and pl_eop() should close it. Do NOT open files in both pl_init() and pl_bop() or close files in both pl_eop() and pl_tidy(). It is recommended that when adding new functions to only a certain driver, the escape function be used. Otherwise it is necessary to add a null routine to all the other drivers to handle the new function.