DCL:GRPH1:SZPACK: The Basic Graphics Routines
SZPACK takes apart all graphics elements such as polylines and text into
polylines and tones. Therefore, in the SZPACK, there are 2 basic systems of
graphics routines; the polyline and the tone. The interface routines
corresponding to each primitive of the SGPACk exist above these two.
Both the polyline and tone graphics routines have the structure in which the
necessary coordinate points are specified between the open and close routines. Routines
exist for each coordinate transformation or clipping units from routines in the
highest UC to those in the lowest RC.
Even in the higher interface routines, there are open and close routines, and
the graphics routines that are called in between them are available to the user.
(The basic graphics routine called from open to close are grouped into one, and
they correspond to the primitives in SGPACK.) When the open routine is called in
a higher interface, settings for attributes, etc. are initialized for each
primitive, and the swoopn (open object) of SWPACK is called. At close,
the swocls (close object) is called.
Each routine in SGPACK basically performs open and close for every primitive,
and the time it take for the open and close process may become extensive
when many primitives with the same attributes are drawn. In such a case, the
process may be made more efficient by drawing multiple primitives between a
single set of open and close routines by using a higher interface routine in the SZPACK.