Name:         PGSHLS

Purpose:      set color representation using HLS system

Category:     GRAPHICS

File:         pgplot.src

Author:       T.J. Pearson

Use:          see description below.

Description:

            SUBROUTINE PGSHLS (CI, CH, CL, CS)
            INTEGER CI
            REAL    CH, CL, CS
      
       Set color representation: i.e., define the color to be
       associated with a color index.  This routine is equivalent to
       PGSCR, but the color is defined in the Hue-Lightness-Saturation
       model instead of the Red-Green-Blue model. Hue is represented
       by an angle in degrees, with red at 120, green at 240,
       and blue at 0 (or 360). Lightness ranges from 0.0 to 1.0, with black
       at lightness 0.0 and white at lightness 1.0. Saturation ranges from
       0.0 (gray) to 1.0 (pure color). Hue is irrelevant when saturation
       is 0.0.
      
       Examples:           H     L     S        R     G     B
           black          any   0.0   0.0      0.0   0.0   0.0
           white          any   1.0   0.0      1.0   1.0   1.0
           medium gray    any   0.5   0.0      0.5   0.5   0.5
           red            120   0.5   1.0      1.0   0.0   0.0
           yellow         180   0.5   1.0      1.0   1.0   0.0
           pink           120   0.7   0.8      0.94  0.46  0.46
      
       Reference: SIGGRAPH Status Report of the Graphic Standards Planning
       Committee, Computer Graphics, Vol.13, No.3, Association for
       Computing Machinery, New York, NY, 1979. See also: J. D. Foley et al,
       ``Computer Graphics: Principles and Practice'', second edition,
       Addison-Wesley, 1990, section 13.3.5.
      
       Argument:
        CI     (input)  : the color index to be defined, in the range 0-max.
                          If the color index greater than the device
                          maximum is specified, the call is ignored. Color
                          index 0 applies to the background color.
        CH     (input)  : hue, in range 0.0 to 360.0.
        CL     (input)  : lightness, in range 0.0 to 1.0.
        CS     (input)  : saturation, in range 0.0 to 1.0.

Updates:      Oct 16, 1998: JPT automatically extracted from source.