| 
	    plgvpd
	  ( | p_xmin, | 
| p_xmax, | |
| p_ymin, | |
| p_ymax ); | 
Get viewport limits in normalized device coordinates.
p_xmin
	  (PLFLT_NC_SCALARReturned value of the lower viewport limit of the normalized device coordinate in x.
p_xmax
	  (PLFLT_NC_SCALARReturned value of the upper viewport limit of the normalized device coordinate in x.
p_ymin
	  (PLFLT_NC_SCALARReturned value of the lower viewport limit of the normalized device coordinate in y.
p_ymax
	  (PLFLT_NC_SCALARReturned value of the upper viewport limit of the normalized device coordinate in y.
Redacted form:
	    General: plgvpd(p_xmin, p_xmax, p_ymin, p_ymax)
	  
This function is used in example 31.