%N pgpt1 %F $MIR/src/pgpt1.f
%D Draw one graph marker
%B
      SUBROUTINE PGPT1 (XPT, YPT, SYMBOL)
      REAL XPT, YPT
      INTEGER SYMBOL

 Primitive routine to draw a single Graph Marker at a specified point.
 The marker is 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
 (XPT,YPT) in world coordinates.

 To draw several markers with coordinates specified by X and Y
 arrays, use routine PGPT.

 Arguments:
  XPT    (input)  : world x-coordinate of the point.
  YPT    (input)  : world y-coordinate of the point.
  SYMBOL (input)  : code number of the symbol to be drawn:
                    -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.
