# coding: utf-8
# original alg from https://github.com/assimp/assimp/issues/4573
# Copyright (C) 2023 Ilia Kurochkin <brothermechanic@yandex.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
__version__ = '0.1'

import math


def shiny_to_rough(shininess):
    ''' convert shiny to roughness '''
    a, b = -1.0, 2.0
    c = (shininess / 100.0) - 1.0
    D = math.pow(b, 2) - (4 * a * c)
    roughness = (-b + math.sqrt(D)) / (2 * a)
    return max(roughness, 0)