# spectralColors.py   V.1.0, Sep 19 2005.

# SpectraLibrary
# Copyright (C) 1998, Earl F. Glynn, Overland Park, KS.
# May be copied freely for non-commercial use.
# Translated from Delpi code from www.efg2.com/Lab


def wavelength2RGB(wavelength):
    """wavelength2RGB(wavelength): given a wavelength in nanometers, return the approximate
    (r,g,b) values in [0,255] for the human vision on screen."""
    # Adapted from www.isc.tamu.edu/~astro/color.html
    gamma = 0.80
    intensityMax = 255

    def adjust(color, factor):
        if color == 0.0:
            return 0 #  Don't want 0^x = 1 for x != 0
        else:
            result = intensityMax * ((color*factor) ** gamma)
            return int(round(result))

    # Here a "caseof" can be really useful!
    int_wavelength = int(wavelength)
    if 380 <= int_wavelength <= 439:
        red   = -(wavelength - 440) / (440 - 380)
        green = 0.0
        blue  = 1.0
    elif 440 <= int_wavelength <= 489:
        red   = 0.0
        green = (wavelength - 440) / (490 - 440)
        blue  = 1.0
    elif 490 <= int_wavelength <= 509:
        red   = 0.0
        green = 1.0
        blue  = -(wavelength - 510) / (510 - 490)
    elif 510 <= int_wavelength <= 579:
        red   = (wavelength - 510) / (580 - 510)
        green = 1.0
        blue  = 0.0
    elif 580 <= int_wavelength <= 644:
        red   = 1.0
        green = -(wavelength - 645) / (645 - 580)
        blue  = 0.0
    elif 645 <= int_wavelength <= 780:
        red   = 1.0
        green = 0.0
        blue  = 0.0
    else:
        red   = 0.0
        green = 0.0
        blue  = 0.0

    # let the intensity fall off near the vision limits
    if 380 <= int_wavelength <= 419:
        factor = 0.3 + 0.7*(wavelength - 380) / (420 - 380)
    elif 420 <= int_wavelength <= 700:
        factor = 1.0
    elif 701 <= int_wavelength <= 780:
        factor = 0.3 + 0.7*(780 - wavelength) / (780 - 700)
    else:
        factor = 0.0

    return adjust(red, factor), adjust(green, factor), adjust(blue, factor)


def rainbowColor(fraction, wavelengthMinimum=380, wavelengthMaximum=780):
    """rainbowColor(fraction, wavelengthMinimum=380, wavelengthMaximum=780):
    return spectrum colors for fraction between 0.0 to 1.0. Wavelengths are in Nanometers."""
    wl = wavelengthMinimum + fraction*(wavelengthMaximum - wavelengthMinimum)
    wl = max(wavelengthMinimum, min(wl, wavelengthMaximum))
    return wavelength2RGB(wl)


if __name__ == '__main__': # Demo
    from Tkinter import *
    root = Tk()
    nx,ny = 500, 50
    c = Canvas(root, width=nx, height=ny)
    c.pack()
    for x in xrange(nx):
        spectCol = "#%02x%02x%02x" % rainbowColor(float(x)/(nx-1))
        c.create_line(x,0, x,ny, fill=spectCol)
    root.mainloop()