/*
 * Bael'Zharon's Respite
 * Copyright (C) 2014 Daniel Skorupski
 *
 * 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 2 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.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
#ifndef BZR_GRAPHICS_SKYMODEL_H
#define BZR_GRAPHICS_SKYMODEL_H

class SkyModel
{
public:
    struct Params
    {
        // dt is the day of the year, between 0 and 365
        fp_t dt;

        // tm is a normalized value, 0 indicating midnight, 0.5 indicating noon
        fp_t tm;

        // lng is in radians, -pi to pi
        fp_t lng;

        // lat is in radians, -pi to pi
        fp_t lat;

        // tu is the turbidity, or haziness, of the sky
        // rough scale of values:
        //   1 pure air
        // 1.5 very clear
        // 2.5 clear
        //   8 light haze
        //  24 haze
        //  48 thin fog
        fp_t tu;
    };

    // prepare for getColor to be called
    void prepare(const Params& p);

    // theta is the zenith angle (angle from directly above)
    // phi is the azimuth angle (ccw angle from directly south)
    // returns a normalized sRGB color value
    glm::vec3 getColor(fp_t theta, fp_t phi);

    fp_t thetaSun() const;
    fp_t phiSun() const;

private:
    // zenith angle of the sun
    fp_t theta_s_;

    // azimuth angle of the sun
    fp_t phi_s_;

    // A, B, C, D and E coefficients for F()
    fp_t coeffs_Y_[5];
    fp_t coeffs_x_[5];
    fp_t coeffs_y_[5];

    // color at zenith
    fp_t Y_z_;
    fp_t x_z_;
    fp_t y_z_;
};

#endif