lua/kanagawa/lib/hsluv.lua
--[[
Lua implementation of HSLuv and HPLuv color spaces
Homepage: http://www.hsluv.org/

Copyright (C) 2019 Alexei Boronine

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
associated documentation files (the "Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the
following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial
portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
]]

local hsluv = {}

local hexChars = "0123456789abcdef"


local distance_line_from_origin = function(line)
    return math.abs(line.intercept) / math.sqrt((line.slope ^ 2) + 1)
end

local length_of_ray_until_intersect = function(theta, line)
    return line.intercept / (math.sin(theta) - line.slope * math.cos(theta))
end

hsluv.get_bounds = function(l)
    local result = {};
    local sub2;
    local sub1 = ((l + 16) ^ 3) / 1560896;
    if sub1 > hsluv.epsilon then
        sub2 = sub1;
    else
        sub2 = l / hsluv.kappa;
    end

    for i = 1, 3 do
        local m1 = hsluv.m[i][1];
        local m2 = hsluv.m[i][2];
        local m3 = hsluv.m[i][3];

        for t = 0, 1 do
            local top1 = (284517 * m1 - 94839 * m3) * sub2;
            local top2 = (838422 * m3 + 769860 * m2 + 731718 * m1) * l * sub2 - 769860 * t * l;
            local bottom = (632260 * m3 - 126452 * m2) * sub2 + 126452 * t;
            table.insert(result, {
                slope = top1 / bottom,
                intercept = top2 / bottom
            })
        end;
    end;
    return result
end

hsluv.max_safe_chroma_for_l = function(l)
    local bounds = hsluv.get_bounds(l);
    local min = 1.7976931348623157e+308;

    for i = 1, 6 do
        local length = distance_line_from_origin(bounds[i]);
        if length >= 0 then
            min = math.min(min, length);
        end;
    end;
    return min;
end

hsluv.max_safe_chroma_for_lh = function(l, h)
    local hrad = h / 360 * math.pi * 2;
    local bounds = hsluv.get_bounds(l);
    local min = 1.7976931348623157e+308;

    for i = 1, 6 do
        local bound = bounds[i];
        local length = length_of_ray_until_intersect(hrad, bound);
        if length >= 0 then
            min = math.min(min, length);
        end;
    end;
    return min
end

hsluv.dot_product = function(a, b)
    local sum = 0;
    for i = 1, 3 do
        sum = sum + a[i] * b[i];
    end;
    return sum
end

hsluv.from_linear = function(c)
    if c <= 0.0031308 then
        return 12.92 * c
    else
        return 1.055 * (c ^ 0.416666666666666685) - 0.055
    end;
end

hsluv.to_linear = function(c)
    if c > 0.04045 then
        return ((c + 0.055) / 1.055) ^ 2.4
    else
        return c / 12.92
    end;
end

hsluv.xyz_to_rgb = function(tuple)
    return {
        hsluv.from_linear(hsluv.dot_product(hsluv.m[1], tuple)),
        hsluv.from_linear(hsluv.dot_product(hsluv.m[2], tuple)),
        hsluv.from_linear(hsluv.dot_product(hsluv.m[3], tuple))
    }
end

hsluv.rgb_to_xyz = function(tuple)
    local rgbl = {
        hsluv.to_linear(tuple[1]),
        hsluv.to_linear(tuple[2]),
        hsluv.to_linear(tuple[3])
    };
    return {
        hsluv.dot_product(hsluv.minv[1], rgbl),
        hsluv.dot_product(hsluv.minv[2], rgbl),
        hsluv.dot_product(hsluv.minv[3], rgbl)
    }
end

hsluv.y_to_l = function(Y)
    if Y <= hsluv.epsilon then
        return Y / hsluv.refY * hsluv.kappa
    else
        return 116 * ((Y / hsluv.refY) ^ 0.333333333333333315) - 16
    end;
end

hsluv.l_to_y = function(L)
    if L <= 8 then
        return hsluv.refY * L / hsluv.kappa
    else
        return hsluv.refY * (((L + 16) / 116) ^ 3)
    end;
end

hsluv.xyz_to_luv = function(tuple)
    local X = tuple[1];
    local Y = tuple[2];
    local divider = X + 15 * Y + 3 * tuple[3];
    local varU = 4 * X;
    local varV = 9 * Y;
    if divider ~= 0 then
        varU = varU / divider;
        varV = varV / divider;
    else
        varU = 0;
        varV = 0;
    end
    local L = hsluv.y_to_l(Y);
    if L == 0 then
        return { 0, 0, 0 }
    end;
    return { L, 13 * L * (varU - hsluv.refU), 13 * L * (varV - hsluv.refV) }
end

hsluv.luv_to_xyz = function(tuple)
    local L = tuple[1];
    local U = tuple[2];
    local V = tuple[3];
    if L == 0 then
        return { 0, 0, 0 }
    end;
    local varU = U / (13 * L) + hsluv.refU;
    local varV = V / (13 * L) + hsluv.refV;
    local Y = hsluv.l_to_y(L);
    local X = 0 - (9 * Y * varU) / ((((varU - 4) * varV) - varU * varV));
    return { X, Y, (9 * Y - 15 * varV * Y - varV * X) / (3 * varV) }
end

hsluv.luv_to_lch = function(tuple)
    local L = tuple[1];
    local U = tuple[2];
    local V = tuple[3];
    local C = math.sqrt(U * U + V * V);
    local H
    if C < 0.00000001 then
        H = 0;
    else
        H = math.atan2(V, U) * 180.0 / 3.1415926535897932;
        if H < 0 then
            H = 360 + H;
        end;
    end;
    return { L, C, H }
end

hsluv.lch_to_luv = function(tuple)
    local L = tuple[1];
    local C = tuple[2];
    local Hrad = tuple[3] / 360.0 * 2 * math.pi;
    return { L, math.cos(Hrad) * C, math.sin(Hrad) * C };
end

hsluv.hsluv_to_lch = function(tuple)
    local H = tuple[1];
    local S = tuple[2];
    local L = tuple[3];
    if L > 99.9999999 then
        return { 100, 0, H }
    end;
    if L < 0.00000001 then
        return { 0, 0, H }
    end;
    return { L, hsluv.max_safe_chroma_for_lh(L, H) / 100 * S, H }
end

hsluv.lch_to_hsluv = function(tuple)
    local L = tuple[1];
    local C = tuple[2];
    local H = tuple[3];
    local max_chroma = hsluv.max_safe_chroma_for_lh(L, H)
    if L > 99.9999999 then
        return { H, 0, 100 }
    end;
    if L < 0.00000001 then
        return { H, 0, 0 }
    end;

    return { H, C / max_chroma * 100, L }
end

hsluv.hpluv_to_lch = function(tuple)
    local H = tuple[1];
    local S = tuple[2];
    local L = tuple[3];
    if L > 99.9999999 then
        return { 100, 0, H }
    end;
    if L < 0.00000001 then
        return { 0, 0, H }
    end;
    return { L, hsluv.max_safe_chroma_for_l(L) / 100 * S, H }
end

hsluv.lch_to_hpluv = function(tuple)
    local L = tuple[1];
    local C = tuple[2];
    local H = tuple[3];
    if L > 99.9999999 then
        return { H, 0, 100 }
    end;
    if L < 0.00000001 then
        return { H, 0, 0 }
    end;
    return { H, C / hsluv.max_safe_chroma_for_l(L) * 100, L }
end

hsluv.rgb_to_hex = function(tuple)
    local h = "#";
    for i = 1, 3 do
        local c = math.floor(tuple[i] * 255 + 0.5);
        local digit2 = math.fmod(c, 16);
        local x = (c - digit2) / 16;
        local digit1 = math.floor(x);
        h = h .. string.sub(hexChars, digit1 + 1, digit1 + 1)
        h = h .. string.sub(hexChars, digit2 + 1, digit2 + 1)
    end;
    return h
end

hsluv.hex_to_rgb = function(hex)
    hex = string.lower(hex)
    local ret = {}
    for i = 0, 2 do
        local char1 = string.sub(hex, i * 2 + 2, i * 2 + 2);
        local char2 = string.sub(hex, i * 2 + 3, i * 2 + 3);
        local digit1 = string.find(hexChars, char1) - 1
        local digit2 = string.find(hexChars, char2) - 1
        ret[i + 1] = (digit1 * 16 + digit2) / 255.0;
    end;
    return ret
end

hsluv.lch_to_rgb = function(tuple)
    return hsluv.xyz_to_rgb(hsluv.luv_to_xyz(hsluv.lch_to_luv(tuple)))
end

hsluv.rgb_to_lch = function(tuple)
    return hsluv.luv_to_lch(hsluv.xyz_to_luv(hsluv.rgb_to_xyz(tuple)))
end

hsluv.hsluv_to_rgb = function(tuple)
    return hsluv.lch_to_rgb(hsluv.hsluv_to_lch(tuple))
end

hsluv.rgb_to_hsluv = function(tuple)
    return hsluv.lch_to_hsluv(hsluv.rgb_to_lch(tuple))
end

hsluv.hpluv_to_rgb = function(tuple)
    return hsluv.lch_to_rgb(hsluv.hpluv_to_lch(tuple))
end

hsluv.rgb_to_hpluv = function(tuple)
    return hsluv.lch_to_hpluv(hsluv.rgb_to_lch(tuple))
end

hsluv.hsluv_to_hex = function(tuple)
    return hsluv.rgb_to_hex(hsluv.hsluv_to_rgb(tuple))
end

hsluv.hpluv_to_hex = function(tuple)
    return hsluv.rgb_to_hex(hsluv.hpluv_to_rgb(tuple))
end

hsluv.hex_to_hsluv = function(s)
    return hsluv.rgb_to_hsluv(hsluv.hex_to_rgb(s))
end

hsluv.hex_to_hpluv = function(s)
    return hsluv.rgb_to_hpluv(hsluv.hex_to_rgb(s))
end

hsluv.m = {
    { 3.240969941904521, -1.537383177570093, -0.498610760293 },
    { -0.96924363628087, 1.87596750150772, 0.041555057407175 },
    { 0.055630079696993, -0.20397695888897, 1.056971514242878 }
}
hsluv.minv = {
    { 0.41239079926595, 0.35758433938387, 0.18048078840183 },
    { 0.21263900587151, 0.71516867876775, 0.072192315360733 },
    { 0.019330818715591, 0.11919477979462, 0.95053215224966 }
}
hsluv.refY = 1.0
hsluv.refU = 0.19783000664283
hsluv.refV = 0.46831999493879
hsluv.kappa = 903.2962962
hsluv.epsilon = 0.0088564516

return hsluv
