/*****************************************************************************
*                                                                            *
*   RAINBOW.SPL    Copyright (C) 1997 DSP Development Corporation            *
*                               All Rights Reserved                          *
*                                                                            *
*   Author:      Randy Race                                                  *
*                                                                            *
*   Synopsis:    Generate a colormap of the visible color spectrum           *
*                                                                            *
*   Revisions:    4 Aug 1997  RRR  Creation                                  *
*                                                                            *
*****************************************************************************/


#if @HELP_RAINBOW

    RAINBOW

    Purpose: Generates a colormap of the visible color spectrum.

    Syntax:  RAINBOW(len)

               len - optional colormap length, defaults to
                     the length of the current colormap


    Returns: A table of RGB triples suitable for the SETCOLORMAP function.

    Example:

             clen = length(getcolormap());
             density(ravel(rep(0..(clen-1), 32), clen)');
             rainbow();

             Creates a table of 32 x colormap length RBG values and
             displays the resulting colors. The resulting image is a
             vertical plot of colors ranging from blue (lowest) to red
             (highest).

     Remarks:

             Rainbow() by itself sets the colormap and shading.

             a = rainbow() or setcolormap(rainbow()) returns the rgb values.
             In this case, use SETSHADING to make the new colormap
             take effect on an existing density or 2D plot.

     See Also:

             Cool
             Hot
             Setcolormap
             Setshading
             Showcmap

#endif


/*
 *  create a colomap of the visible color spectrum ranging
 *  from blue to red
 */

rainbow(cmaplen)
{
        local n, a, b, c, r, g, b, rgb;

        if (argc < 1)
        {
                /* set size to current colormap size */
                cmaplen = length(getcolormap());
        }

        n = maxval(round(cmaplen / 4), 1);
        a = (1..n) / n;
        b = ((n / 2)..n) / n;
        c = ones(length(a), 1);

        /* generate rbg values */
        r = {0*b, 0*c, a, c, rev(b)};
        g = {0*b, a, c, rev(a), 0*b};
        b = {b, c, rev(a), 0*c, 0*b};

        rgb = ravel(r, g, b);

        if (length(rgb) > cmaplen)
        {
                rgb = extract(rgb, int((length(rgb) - cmaplen) / 2) + 1, cmaplen);
        }

        if (outargc == 0)
        {
                /* set the colormap and shading */
                setplotshading(rgb);
        }
        else
        {
                /* return the colormap */
                setrgbprops(rgb);
                
                return(rgb);
        }
}