local p = {}



local redvalue = 0

local greenvalue = 0

local bluevalue = 0

 

local function nm2RGB(wavelength, IFcorrect)

-- code based on an algorithm from Dan Bruton's Color Science Page: http://www.physics.sfasu.edu/astro/color/spectra.html

-- calculating RGB color components

    if (wavelength >= 380) and (wavelength < 440) then

        redvalue = (440 - wavelength) / 90

        greenvalue = 0

        bluevalue = 1

    elseif (wavelength >= 440) and (wavelength < 490) then

        redvalue = 0

        greenvalue = (wavelength - 440) / 50

        bluevalue = 1

    elseif (wavelength >= 490) and (wavelength < 510) then

        redvalue = 0

        greenvalue = 1

        bluevalue = (510 - wavelength) / 20

    elseif (wavelength >= 510) and (wavelength < 580) then

        redvalue = (wavelength - 510) / 70

        greenvalue = 1

        bluevalue = 0

    elseif (wavelength >= 580) and (wavelength < 645) then

        redvalue = 1

        greenvalue = (645 - wavelength) / 65

        bluevalue = 0

    elseif (wavelength >= 645) and (wavelength <= 780) then

        redvalue = 1

        greenvalue = 0

        bluevalue = 0

    end

-- calculating intensity correction factor

    if IFcorrect then

    local intensityfactor = 0

    if (wavelength >= 380) and (wavelength < 420) then

        intensityfactor = 0.3 + 0.7*(wavelength - 350) / 70

    elseif (wavelength >= 420) and (wavelength <= 700) then

        intensityfactor = 1

    elseif (wavelength > 700) and (wavelength <= 780) then

        intensityfactor = 0.3 + 0.7*(780 - wavelength) / 80

    end

    redvalue = redvalue * intensityfactor

    greenvalue = greenvalue * intensityfactor

    bluevalue = bluevalue * intensityfactor

    end

end



function p.emission(frame)

-- this function returns the string "#RRGGBB" with approximate RGB value for a wavelength passed as a first argument

    local wavelength = tonumber(frame.args1])

    nm2RGB(wavelength, true)

    local result='#' .. string.format("%.2X%.2X%.2X", 255*redvalue, 255*greenvalue, 255*bluevalue) 

    return result

end



local function absorption_to_visible(wavelength_abs)

-- code based on a color wheel drawn at: http://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/spectrpy/uv-vis/spectrum.htm

   local wavelength_vis

   local minVioletIndigo = 380 -- originally, it was 400

   local maxVioletIndigo = 430

   local widthVioletIndigo = maxVioletIndigo - minVioletIndigo

   local minBlue = 430

   local maxBlue = 490

   local widthBlue = maxBlue - minBlue

   local minGreen = 490

   local maxGreen = 560

   local widthGreen = maxGreen - minGreen

   local minYellow = 560

   local maxYellow = 580

   local widthYellow = maxYellow - minYellow

   local minOrange = 580

   local maxOrange = 650 -- originally, it was 620

   local widthOrange = maxOrange - minOrange

   local minRed = 650 -- originally, it was 620

   local maxRed = 780 -- originally, it was 800

   local widthRed = maxRed - minRed

   if (wavelength_abs>=minVioletIndigo) and (wavelength_abs<=maxVioletIndigo) then

      wavelength_vis = (wavelength_abs - minVioletIndigo)*widthYellow/widthVioletIndigo + minYellow

   elseif (wavelength_abs>minBlue) and (wavelength_abs<=maxBlue) then

      wavelength_vis = (wavelength_abs - minBlue)*widthOrange/widthBlue + minOrange

   elseif (wavelength_abs>minGreen) and (wavelength_abs<=maxGreen) then

      wavelength_vis = (wavelength_abs - minGreen)*widthRed/widthGreen + minRed

   elseif (wavelength_abs>minYellow) and (wavelength_abs<=maxYellow) then

      wavelength_vis = (wavelength_abs - minYellow)*widthVioletIndigo/widthYellow + minVioletIndigo

   elseif (wavelength_abs>minOrange) and (wavelength_abs<=maxOrange) then

      wavelength_vis = (wavelength_abs - minOrange)*widthBlue/widthOrange + minBlue

   elseif (wavelength_abs>minRed) and (wavelength_abs<=maxRed) then

      wavelength_vis = (wavelength_abs - minRed)*widthGreen/(widthRed + 20) + minGreen

-- one of the "corrected" versions: wavelength_vis = (wavelength_abs - minRed - 30)*widthGreen/widthRed + minGreen

   end

   return wavelength_vis

end



local minAntiMagenta = 550

local maxAntiMagenta = 570



local function process_magenta(wavelength_abs)

   local redvalue_RED

   local bluevalue_RED

   local greenvalue_RED

   local redvalue_BLUE

   local bluevalue_BLUE

   local greenvalue_BLUE

   local widthAntiMagenta = maxAntiMagenta - minAntiMagenta

   local bias_BLUE = (wavelength_abs - minAntiMagenta)/widthAntiMagenta

   local bias_RED = (maxAntiMagenta - wavelength_abs)/widthAntiMagenta

   nm2RGB(700, false)

   redvalue_RED = redvalue*bias_RED

   bluevalue_RED = bluevalue*bias_RED

   greenvalue_RED = greenvalue*bias_RED

   nm2RGB(400, false)

   redvalue_BLUE = redvalue*bias_BLUE

   bluevalue_BLUE = bluevalue*bias_BLUE

   greenvalue_BLUE = greenvalue*bias_BLUE

   redvalue = 0.6+ 0.4*(redvalue_RED + redvalue_BLUE)

   bluevalue = 0.7 + 0.3*(bluevalue_RED + bluevalue_BLUE)

   greenvalue = greenvalue_RED + greenvalue_BLUE

end



function p.absorption(frame)

-- this function returns the string "#RRGGBB" with approximate RGB value for a complementary color (reflection) to a color, defined as a wavelength passed as a first argument

    local wavelength = tonumber(frame.args1])

-- adding magentas to smoothen red->blue transition. Trying 540..570 nm

    if (wavelength>=minAntiMagenta) and (wavelength<=maxAntiMagenta) then

       process_magenta(wavelength)

       else nm2RGB(absorption_to_visible(wavelength), false)

    end

    local result='#' .. string.format("%.2X%.2X%.2X", 255*redvalue, 255*greenvalue, 255*bluevalue) 

    return result

end





return p