%N pgpt %F $MIR/src/pgpt.f
%D Draw several graph markers
%B
      SUBROUTINE PGPT (N, XPTS, YPTS, SYMBOL)
      INTEGER N
      REAL XPTS(*), YPTS(*)
      INTEGER SYMBOL

 Primitive routine to draw Graph Markers (polymarker). The markers
 are drawn using the current values of attributes color-index,
 line-width, and character-height (character-font applies if the symbol
 number is >31).  If the point to be marked lies outside the window,
 no marker is drawn.  The "pen position" is changed to
 (XPTS(N),YPTS(N)) in world coordinates (if N > 0).

 Arguments:
  N      (input)  : number of points to mark.
  XPTS   (input)  : world x-coordinates of the points.
  YPTS   (input)  : world y-coordinates of the points.
  SYMBOL (input)  : code number of the symbol to be drawn at each 
                    point:
                    -1, -2  : a single dot (diameter = current
                              line width).
                    -3..-31 : a regular polygon with ABS(SYMBOL)
                              edges (style set by current fill style).
                    0..31   : standard marker symbols.
                    32..127 : ASCII characters (in current font).
                              e.g. to use letter F as a marker, let
                              SYMBOL = ICHAR('F'). 
                    > 127  :  a Hershey symbol number.

 Note: the dimension of arrays X and Y must be greater than or equal
 to N. If N is 1, X and Y may be scalars (constants or variables). If
 N is less than 1, nothing is drawn.
