/*
 * This program source code file is part of KiCad, a free EDA CAD application.
 *
 * Copyright (C) 2015-2016 Mario Luzeiro <mrluzeiro@ua.pt>
 * Copyright (C) 2015-2020 KiCad Developers, see AUTHORS.txt for contributors.
 *
 * 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, you may find one here:
 * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 * or you may search the http://www.gnu.org website for the version 2 license,
 * or you may write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 */

/**
 * @file light.h
 * @brief Declare and implement light sources.
 */

#ifndef _LIGHT_H_
#define _LIGHT_H_

#include "ray.h"
#include "hitinfo.h"


/**
 * A base light class to derive to implement other light classes.
 */
class LIGHT
{
public:
    LIGHT() { m_castShadow = true; }

    virtual ~LIGHT() {}

    /**
     * Get parameters from this light.
     *
     * @param aHitPoint: input hit position
     * @param aOutVectorToLight a vector that points from the hit
     *                          position in direction to the light
     * @param aOutLightColor the color of this light
     * @param aOutDistance the distance from the point to the light
     */
    virtual void GetLightParameters( const SFVEC3F& aHitPoint, SFVEC3F& aOutVectorToLight,
                                     SFVEC3F& aOutLightColor, float& aOutDistance ) const = 0;

    void SetCastShadows( bool aCastShadow ) { m_castShadow = aCastShadow; }
    bool GetCastShadows() const { return m_castShadow; }

protected:
    bool m_castShadow;
};


/**
 * Point light source based on http://ogldev.atspace.co.uk/www/tutorial20/tutorial20.html.
 */
class POINT_LIGHT : public LIGHT
{
public:
    POINT_LIGHT( const SFVEC3F& aPos, const SFVEC3F& aColor )
    {
        m_position     = aPos;
        m_color        = aColor;
        m_att_constant = 0.9f;
        m_att_linear   = 0.0005f;
        m_att_exp      = 0.001f;
        m_castShadow   = true;
    }

    // Imported functions from LIGHT
    void GetLightParameters( const SFVEC3F& aHitPoint, SFVEC3F& aOutVectorToLight,
                             SFVEC3F& aOutLightColor, float& aOutDistance ) const override
    {
        const SFVEC3F vectorLight = m_position - aHitPoint;

        aOutDistance = glm::length( vectorLight );
        aOutVectorToLight = vectorLight / aOutDistance; // normalize

        const float att = 1.0f / ( m_att_constant +
                                   m_att_linear   * aOutDistance +
                                   m_att_exp      * aOutDistance * aOutDistance );

        if( att <= 0.0f )
            aOutLightColor = SFVEC3F( 0.0f, 0.0f, 0.0f );
        else
            aOutLightColor = m_color * att;
    }

private:
    SFVEC3F m_position;
    SFVEC3F m_color;

    float   m_att_constant;
    float   m_att_linear;
    float   m_att_exp;
};


/**
 * A light source based only on a directional vector.
 */
class DIRECTIONAL_LIGHT : public LIGHT
{
public:
    DIRECTIONAL_LIGHT( const SFVEC3F& aDir, const SFVEC3F& aColor )
    {
        // Invert light direction and make sure it is normalized
        m_inv_direction = glm::normalize( -aDir );
        m_color         = aColor;
        m_castShadow    = true; // Set as default to cast shadows
    }

    /**
     * Set directional light orientation.
     *
     * @param aDir is the vector defining the direction of the light source.
     */
    void SetDirection( const SFVEC3F& aDir ) { m_inv_direction = -aDir; }

    // Imported functions from LIGHT
    void GetLightParameters( const SFVEC3F& aHitPoint, SFVEC3F& aOutVectorToLight,
                             SFVEC3F& aOutLightColor, float& aOutDistance ) const override
    {
        (void)aHitPoint; // unused

        aOutVectorToLight = m_inv_direction;
        aOutDistance      = std::numeric_limits<float>::infinity();
        aOutLightColor    = m_color;
    }

private:
    SFVEC3F m_inv_direction;        ///< opposite direction of the light
    SFVEC3F m_color;                ///< light color
};


#endif // _LIGHT_H_