The GSTART subroutine initializes the graphics system the first time it is called. A catalog is opened to capture any graphics segments generated in the session. If you do not specify a catalog, PROC IML uses the temporary catalog Work.Gseg.

The arguments to the GSTART subroutine are as follows:

The replace argument is a flag; a nonzero value indicates that the new segment should replace the first found segment with the same name. The replace flag set by the GSTART subroutine is a global flag, as opposed to the replace flag set by the GOPEN subroutine. When set by GSTART, this flag is applied to all subsequent segments created for this catalog, whereas with GOPEN, the replace flag is applied only to the segment that is being created. The GSTART subroutine sets the replace flag to 0 when the replace argument is omitted. The replace option can be very inefficient for a catalog with many segments. In this case, it is better to create segments with different names (if necessary) than to use the replace option.

The GSTART subroutine must be called at least once to load the graphics subsystem. Any subsequent GSTART calls are generally to change graphics catalogs or reset the global replace flag.

The GSTART subroutine resets the defaults for all graphics attributes that can be changed by the GSET subroutine. It does not reset GOPTIONS to their defaults unless the GOPTION corresponds to a GSET parameter. The GOPEN subroutine also resets GSET parameters.

An example of using the GSTART subroutine is provided in the documentation for the GPOINT subroutine.