Function:     GREXEC

Purpose:      Interface to device drivers for plot system.

Category:     PLOTTING

Files:        pgdriv.src

Author:       K.G. Begeman

Use:          CALL GREXEC( IDEV ,         Input        INTEGER
                           IFUNC ,        Input        INTEGER
                           RBUF ,      Input/Output    REAL ARRAY
                           NBUF ,      Input/Output    INTEGER
                           CHR ,       Input/Output    CHARACTER*(*)
                           LCHR )      Input/Output    INTEGER

              IDEV         Device identifier for PGPLOT.
              IFUNC        Wanted graphics function.
              RBUF         Real buffer.
              NBUF         Number of items in RBUF.
              CHR          Character buffer.
              LCHR         Number of items in CHR.

Description:  The device information is stored in a text file
              ("gip_loc:grdevices") which is read by GREXEC.

Updates:      Jan 15, 1991: KGB Document created.
              Oct 13, 1992: JPT tHermes tek driver code added
              Jan 28, 1997: JPT support for loadable drivers added
              Aug 13, 2004: JPT support for exported Ggi drivers added
              May 18, 2012: JPT support for special Ggi device "SCREEN"